BEAMFORMING METHOD, MEASUREMENT AND IMAGING INSTRUMENTS, AND COMMUNICATION INSTRUMENTS

[0001] The present application claims priority from Japanese Patent Applications No. 2014-116949 filed on Jun. 5, 2014 (inventor: Dr. Chikayoshi Sumi, an associate professor at Sophia University, Tokyo Japan), No. 2014-165284 filed on Aug. 14, 2014 (inventors: Dr. Chikayoshi Sumi and Mr. Naoto Yamazaki, a master degree student at Sophia University, Tokyo Japan), No. 2015-046528 filed on Mar. 9, 2015 (Dr. Chikayoshi Sumi), No. 2015-087901 filed on Apr. 22, 2015 (Dr. Chikayoshi Sumi), and No. 2015-106798 filed on May 26, 2015 (Dr. Chikayoshi Sumi), the contents of which are incorporated herein by reference in their entirety.

[0002] 1. Field of the Invention

[0003] The present invention relates to beamforming methods that are used for beamforming on arbitrary waves that arrive from measurement objects. The present invention also relates to measurement and imaging instruments, and communication instruments using such beamforming methods.

[0004] Particularly, the present invention relates to digital beamforming methods used in instruments that perform, on the basis of arbitrary waves such as electromagnetic waves, lights, mechanical vibrations, acoustic waves, thermal waves etc. that arrive from measurement objects, imaging of the objects, or non-destructively measuring and imaging of physical quantities such as temperatures, displacements etc., compositions and structures etc. of the objects. The measurement objects are various such as organic and inorganic substances or matters, solids, liquids, gases, rheology matters, living things, celestial objects, an earth, environments etc., and the application range is prominently widespread.

[0005] The present invention relates to nondestructive evaluations, diagnoses, resource explorations, growth and manufacturing of substances and structures, monitoring of physical and chemical restorations and treatments, applications of clarified functions and physical properties etc., where a high measurement accuracy can be required to be achieved without generating turbulences under the conditions of a noninvasiveness, a low invasiveness, no observable blood etc. Ideally, the measurement objects should be observed at their original positions in situ.

[0006] Measurement objects can also be treated or restored owing to the actions of the waves themselves. Simultaneously, the processes can also be observed by performing the beamforming using the responses from the objects. Beamforming is also performed on satellite communications, radars, sonars etc. to perform accurate communications under saving energies by realizing informationally safe environments. In ad hoc communication instruments and mobile instruments, beamforming has also been used. When the objects are dynamic, real time characteristics is demanded and therefore, the beamforming is required to be completed in a short time.

[0007] 2. Description of a Related Art

[0008] Behaviors of waves such as electromagnetic waves, lights, mechanical vibrations, acoustic waves, thermal waves etc. are different on their frequencies, bandwidths, intensities, modes etc. Many transducers of various waves are developed so far, and imaging with the transmission waves, reflection waves, refracted waves or scattered waves (forward or back scattered waves) etc. is performed.

[0009] For instance, it is well known that a higher frequency acoustic wave categorized into an ultrasound is used for non-destructive evaluations, a medicine and sonars. For radars, proper frequency electromagnetic waves such as a radio wave, an FM wave, a micro wave, a terahertz wave, an infrared wave, a visible wave, a violet wave, a radioactive ray such as an X-ray etc. are used. Also for other waves, the behavior is different and dependent on the frequency and therefore it has a specific name, which is used for various sensing and communications properly with respect to measurement objects, media and bandwidths (polarization can also be performed on electromagnetic waves).

[0010] By those applications, the measurement objects are often scanned with a transducer mechanically. Also the same transducer is often used plural times, or plural transducers aligned in an array form beforehand are often used to perform beamforming processing. It is well known that when the earth and land, the ocean, weather are observed by the radar of a satellite and an airplane, a synthetic aperture processing etc. is performed. When imaging of the measurement objects in particular, an appropriate directivity is kept, and the beamforming is often intended that a high spatial resolution and a high contrast are achieved in a region of interest or at a point of interest.

[0011] As a result, a reflection and transmission generated by a spatial change of the impedance, various scattering (Rayleigh scattering, Mie scattering, and others), attenuation or those frequency variance etc. acting on a wave in the measurement object can be observed, and the inside and surface structures and compositions can be observed in addition to what the measurement object is. The measurement object can also be observed in a various spatial resolution. At various levels of the structure and composition (e.g., an individual level, a molecular level, an atom level, a nuclear level etc.), characteristic evaluations (characterization) can be performed.

[0012] For the purpose of highly accuracy, high-spatial resolution imaging, the signal compression technique such as a charp technology and an encoding technique have been representatively used for a long time. In ISAR (inverse synthetic aperture radar) etc., the inversion of beam properties is implemented on an observed signal to generate a super-resolution (e.g., when performing SA or others). Alternatively, a spatial resolution may also be reduced positively. For their processing, the singular value decomposition (SVD), the regularization, the Wiener filtering etc. are effective.

[0013] In addition, the encoding technology is also used for separating the simultaneously received signals into the respective signals, e.g., for a reception signal with respect to plural transmitted signals with different transmission positions. The waves to come from the different directions can be separated, and a signal source can be separated or identified. In such cases, matched filtering that achieves a high signal detection is great. However, when signal energy is obtained, but on the other hand, the object movement with the deformation, and the object displacement and strain etc. decrease the spatial resolution of signals, and therefore, the measurement accuracy is decreased as well. For the separation of waves and signals, the use of frequency and bandwidth or multidimensional spectra is also useful.

[0014] For imagings with the waves mentioned above, the distribution of amplitude data provided through quadrature detection and envelope detection or square detection is displayed as a gray image and a color image in one dimension, two dimensions or three dimensions, and the imaging often provides morphologic images. In addition, the functional observation is also possible, and for instance, a raw coherent signal is processed in the Doppler measurement using those waves (ultrasound Doppler, Radar Doppler, Laser Doppler etc.).

[0015] In addition, for instance, there is no information of a tissue displacement direction, but the power Doppler used in the medical ultrasound field can detect a tissue with the movement, which is a useful technique. In addition, when using a microwave, a terahertz wave or far infrared rays, the temperature distribution of object can be observed. Those measured physical quantities can be displayed with superposing them on morphologic images. In the field of the image measurement, observation of the movement can also be performed using the incoherent signal obtained through detection of a coherent signal (cross-correlation processing or optical flow etc.). On a medical ultrasound and a sonar, imaging using harmonic waves, and chord and different tone waves generated physically are also carried out. Particularly when a measurement object is dynamic, real time characteristics are demanded for beamforming processing.

[0016] In addition, in satellite communications, radars, sonars etc., beamforming is also performed to realize an informationally safe environment under the energy saving, and accurate communication is performed. In the ad hoc communication instruments and for mobile communications, beamforming has also been applied. Beamforming is also effective for an authorized person and a specific signal outbreak source, the specific communication with the position. In communications, information is put on a wave at the transmission side and sent to the reception side from the transmission side, which can be a purpose, the reception side can also reply to the transmission side by a result of the communication, and can also reply for the transmitted information and communicate again, but, of course, communications are not limited to these examples. When contents are dynamic, depending on a communication object and an observation object, real time characteristics are demanded, and it is demanded that the beamforming in that case is completed in a short time.

[0017] In such communication and medical fields, for instance, the present inventor develops ultrasonic imaging techniques for a differential diagnosis of lesions such as cancerous diseases, sclerosis etc. of human tissues. The present inventor increases a spatial resolution in echo imaging and an accuracy in measurement and imaging of a tissue displacement; and the present inventor also increases a spatial resolution and an efficiency of HIFU (High Intensity Focus Ultrasound) treatment; and the present inventor also promotes those imagings based on the reception of the echo with respect to the HIFU radiation. Those imagings are based on performing appropriate beamforming at high speed and therefore, the present inventor develops and discloses appropriate, high speed detection methods, tissue displacement measurement methods and shear wave propagation measurement methods etc.

[0018] The medical ultrasound diagnosis imaging instrument passed more than 20 years after it was digitized. In old times, mechanical scanning was performed using a single aperture transducer (a single element); and subsequently electronic scanning using plural transducers (elements) and the array type devices consisting of them was performed, and the device which processed a signal changed from an analog device to a digital device afterwards. Actually, the classical synthetic aperture processing itself has been digital beamforming since those days when it came to be used in a radar carried by a satellite and an airborne, but it was rare to be used in a medical ultrasound instrument by the reason of the strength of the reception signal (echo intensity) being weak.

[0019] In contrast, in late years the present inventor invented the multidirectional synthetic aperture method and achieved multidirectional beamforming by using a reception echo data set for a conventional synthetic aperture method. As a result, lateral modulation imaging with a carrier frequency in the lateral direction orthogonal to an axial direction and with a higher spatial resolution than conventional imaging was enabled by becoming able to obtain multidirectionally steered image signals at the frame rate that was the same as that by the conventional electronic scanning, and the coherent superposition (compounding). Besides, a real time measurement was enabled for the displacement vector distribution by using the multidimensional autocorrelation method that the present inventor invented together. In addition, speckle reduction was also enabled by performing incoherent superposition (compounding). Although conventionally transmission beams in different directions were used for the speckle reduction, the invented multidirectional synthetic aperture achieved a higher frame rate speckle reduction. In other sensing devices which use the waves such as a microwave, a terahertz wave, radioactive rays such as an X-ray etc., other electromagnetic waves, vibration waves including a sound, a thermal wave etc. for non-destructive evaluations other than those in ultrasound fields, digitization is pushed forward.

[0020] For instance, the synthetic aperture performed in those sensing instruments is an active beamforming, and the wave to be targeted for processing is a transmission wave, a reflection wave, a refracted wave or a scattered wave (forward or backward scattered wave etc.) with respect to those waves generated by a transducer. On the other hand, for instance, in a passive beamforming, a transmission wave, a reflection wave, a refracted wave or a scattered wave (forward or backward scattered wave etc.) become targets under the assumption that all the waves are generated from a wave emitted from the signal source which is by oneself a divergence targeted for a measurement (self-emanating), so that a case to measure a temperature distribution based on the far infrared observation mentioned above and an electrical activity source by the brain magnetic field of the creature is also. The examples corresponding to them exist much elsewhere. But recently photoacoustics is also targeted for a measurement of living things, and a laser is irradiated to an ultrasound creature as a measurement object (ultrasound source), i.e., a volume change caused by heat absorption with the laser frequency dependence generates an ultrasound, by which peripheral blood vessels can be distinguished as a result of reception beamforming, i.e., arteries or veins, for instance.

[0021] The digital instrument needs a lot of processing time in comparison with an analog instrument, but there are many advantages such as it being easy to implement high level calculation processing, being cheap and downsized including data storage medium, which improves calculation processing capacity and flexibility markedly. Actually, the high-speed analog processing performed immediately after having a received signal is extremely important, and it should be implemented with digital processing after AD conversion (Analogue-to-Digital conversion) relatively considered to be in around of the sensing device appropriately even if the instrument is called as a digital system.

[0022] In the analog instrument, the beamformings of the transmission and reception are carried out by analog processing. On the other hand, in the digital instrument, the transmission beamforming can be carried out by analog processing or digital processing, and the reception beamforming is carried out by digital processing. Thus, in the present invention, a beamformer performing reception beamforming by digital processing by all means is referred to as a digital beamformer.

[0023] After having received the waves from a measurement object through plural transducers (elements), an array type device consisting of them or mechanical scanning with one or more transducers (elements); DAS (Delay and Summation: phasing and summing) that is so-called synthetic aperture processing is carried out. For transmission, plural elements are excited to perform transmission beamforming, or a classical synthetic aperture processing is perform on the basis of one element transmission, whereas for reception beamforming, the DAS processing is performed commonly.

[0024] In other words, the transmission beamforming is carried out by analog processing or digital processing. On the other hand, in the reception beamforming, a reception signal is generated by each element in the array or by each element of the different position; and is AD converted into a digital reception signal after level adjustment of signal amplitude by the analogue amplification or attenuation, or analog filtering etc.; and the digital reception signal of each element is stored into a storage. Afterwards a device or computer, PLD (Programmable Logic Device), FPGA (Field-Programmable Gate Array), DSP (Digital Signal Processor), GPU (Graphical processing Unit) or microprocessor etc. with the general-purpose calculation processing capacity, or a dedicated computer, a dedicated digital circuit or a dedicated device, the digital processing is performed on the stored reception signals.

[0025] The device performing these digital processing can comprise those analog devices or AD converter, memory etc. The device or computer with computing capacity can be multi-cores. These make it possible to carry out a dynamic focusing that is almost impossible with an analog device at the reception. The parallel computations can also be carried out. A transmission line (e.g., multilayer circuit etc.) or a broadband wireless line is important on speeding up the analog processing and digital processing.

[0026] The dynamic focusing improves the spatial resolutions of generated image signals in a range direction or a depth direction for a measurement object. Alternatively, it is possible to perform a transmission dynamic focusing only when performing a classical synthetic aperture using one element transmission. In order to generate energy of a transmitted wave, a fixed focus transmission is often performed using plural excited elements instead of the synthetic aperture using the one element transmission.

[0027] The present inventor developed a high frame rate echo imaging that allowed interrogating a large region using one transmission by using a lateral wide wave such as a plane wave etc. Moreover, the present inventor realized lateral modulation and increasing a lateral bandwidth (a lateral spatial resolution) by performing coherent compounding (superposition) of plural waves with different steering angles. Particularly when using the above-mentioned autocorrelation method, the following displacement vector measurements are enabled, a shear wave propagation, a rapid blood flow in a carotid, a complex flow in a heart etc. When performing the multidirectional synthetic aperture or the transmission beamforming, similarly the imaging and measurement can be achieved. Otherwise, superposing plural waves with different carrier frequencies can also realize increasing an axial bandwidth (an axial spatial resolution).

[0028] For an active beamforming, these processings are performed, whereas for a passive beamforming, a transmitter is not used. Thus, a digital beamformer is comprised of a transmitter (an active beamforming case), a receiver and a DAS processing device, which is realized by building up them. Recently, they are packaged into a small size and can be used.

[0029] Phasing in the DAS processing can performed with a high speed by implementing delays onto a received echo signals via spatial approximate interpolations in a spatial domain, whereas the delays can also be implemented with a high accuracy, but with vast time, on the basis of the Nyquist theorem via phase rotations using multiplications of complex exponential functions in a frequency domain (a present inventor's past invention). After the phasing, the received signals are summed in a spatial domain (phasing and summing). In a digital instrument, for instance, a command signal generated by a control unit and used for transmitter's generating a transmission signal sent to an element to be driven can be used as a trigger signal for digital sampling of an analogue received signal (AD conversion).

[0030] When driving plural elements with transmission delays for a beamforming, one of analogue or digital transmission delay patterns set on a transmit unit in advance can be used for realizing a transmission focus position or a direction of steering etc. to be chosen by an operator. Moreover, in a received digital processing, a command signal used for driving an element at first, at last or other can be used as a trigger signal for starting the sampling of received signals; and the digital delays can be implemented on the digitized, received signals. The command signals can be generated on the basis of a command signal used for starting beamformings for a frame.

[0031] When implementing a digital delay for a transmission delay, an error determined by a clock frequency that generates a digital control signal, which is different from when performing an analogue delay. Thus, for a transmission delay, an analogue delay should be implemented. Alternatively, because for performing a reception dynamic focusing, when implementing a digital delay on to a received signal, an error is caused by the above-mentioned interpolation approximation, the sampling frequency of an AD converter is made sufficiently high with a high cost, or the above-mentioned high accuracy digital delay (phase rotation processing) must be implemented, which leads to a low speed beamforming.

[0032] The phasing and summing performed with the interpolation approximations can be achieved by simply adding echo signals of positions including the position of which an echo signal is synthesized, or by performing interpolations such as a bi-linear or a polynomial fitting etc. to increase the accuracy of the synthesized echo signal. Such beamformings are much faster than the high accuracy phasing and summing using complex exponential functions, but, the accuracy is lower than that of the high accuracy phasing and summing. The high accuracy phasing and summing is much slower. The phasing and summing is performed under the condition that the wave propagation speed is known or under using of an assumed wave propagation speed, for instance, a constant speed in a region of interest (ROI). Alternatively, phase aberration correction can also be performed via measuring of the wave propagation speed. For instance, the phase aberration can be calculated via estimating a cross-correlation function between adjacent beam signals or beam signals with different steering angles. When the wave propagation speed is homogeneous, interferometry analysis is achieved.

[0033] When the aperture elements exist in a 2D region or a 3D space, or a 2D or 3D array is comprised of the aperture elements, the further more processings are required for the beamforming and many processors are used for parallel processing etc. than when the aperture elements exist in a 1D region or a 1D array is comprised of the aperture elements. For the beamforming performed at positions that yield less interferences of transmission waves, the transmission beamforming of plural different directions (different steering angles), a transmission beamforming solo, parallel reception beamforming can be performed.

[0034] For the control of communication, being dependent on a kind of communication data and the data amount, and medium properties, a proper wave should be generated, and an optimized communication should be performed under the observation of them. Interfered waves can also be separated using an analogue device, or analogue or digital signal processing. Waves with controlled propagation directions, encodings, frequencies and/or bandwidths are important.

[0035] The present inventor's another invent similarly to the above-mentioned multidirectional synthetic aperture processing is to perform reception beamformings with plural directions with respect to one transmission beamforming; yielding a high frame rate. Also for the beamforming, apodization can be important. For instance, the respective transmission and reception apodizations can be performed to decrease sidelobes; properly the apodizations should be performed because they have a relation of trade-off with a lateral resolution. Alternatively, a simple beamformer with no apodization can also be used not to decrease the spatial resolution. However, the present inventor has been reporting that for the steering beamforming, proper apodizations are required to yield a high lateral resolution as well as suppressed sidelobes. The present inventor's previous invents include an approach that removing the sidelobes in a frequency domain.

[0036] Agents can be used to use nonlinear properties of waves propagating in an object. For instance, in a medical ultrasound field, microbubbles can be used. The present inventor invented imaging with a high spatial resolution and a high contrast by suppressing the sidelobes via transmitting high intensity waves or waves including harmonic waves, or implementing nonlinear processing onto received coherent signals or phased and summed coherent signals. The present inventor also invented a high accuracy tissue displacement (vector) measurement on the basis of the nonlinear processing.

[0037] Also imaging signals can also be generated using virtual sources. Regarding virtual sources, a virtual source set behind a physical aperture and a virtual source set at a focus position were reported previously. The present inventor also reported a virtual detector as well as a virtual source that is set at an arbitrary position, i.e., including not a focus position, and a proper scatter and a proper diffraction grid with an arbitrary position to be used as a physical wave source or a physical detector etc. A high spatial resolution and a large field of vision (FOV) can be obtained.

[0038] For performing imaging, a quadrature detection, an envelope detection, or a square detection can be used. The present inventor makes much of the using of phase information, e.g., by displaying a waveform itself in a color or gray image. Thus, toward various purposes, various multidimensional systems using various waves are developed.

[0039] As far, several digital beamforming methods using the Fourier's transform were disclosed. One of them is the digitized, analogue processing via the Fourier's transform that is an analytic solution of a classical monostatic synthetic aperture (SA) (nonpatent document 1), i.e., the beamforming that performs the classical synthetic aperture with a high speed and a high accuracy by using the fast Fourier's transform (FFT) (nonpatent document 2). In the processing, any approximate interpolation processing is not required. However, any digital processing for steering and a multistatic SA (receptions using plural elements, generally, including a transmission element and the surrounding elements) has not been disclosed yet.

[0040] All other digital beamforming methods disclosed perform approximate interpolation processings, and then yield low accuracies. For instance, for a plane wave transmission including a steered case, in which a wavenumber matching (mapping) via the FFT (nonpatent documents 3-5) and a non-flat aperture of an array (e.g., the array aperture geometry is an arc (nonpatent document 6)), the calculation and displaying require approximate interpolation processings, and yield low accuracies. The beamformings using the FFT for a plane wave transmission is also disclosed in patent documents 1-4, all of which perforin the wavenumber matching via approximate interpolations. Multidimensional spectra are calculated on a wavenumber coordinate system with constant intervals via the approximate interpolations from directly calculated angular spectra, and the beamforming is completed by implementing the inverse FFT (IFFT).

[0041] In recently published nonpatent document 5, the non-uniform IFFT to be implemented on spectra with non-constant intervals is disclosed, which is also based on an approximate interpolation processing. As mentioned above, although such digital beamforming has already had a long history, because in a case where a real-time processing up to displaying an image is made much of, approximate interpolations are often performed, the highest accuracy is not always provided. Moreover, for the popular beamformings such as a fixed focus processing and steering etc. known to be performed via the DAS processing, any processing method using the digital FFT has not been disclosed yet.

[0042] Also the migration method is also reported (for instance, nonpatent document 7), which also requires approximate interpolation on the wavenumber matching. In order to achieve a high accuracy for these processings with approximate interpolations, sufficient over-samplings are performed by setting the analogue-to-digital (AD) sampling frequency high.

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• [0049] [PATENT DOCUMENT 7] US patent applicant publication 2011/0172538

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[0078] As explained above, because when performing the reception dynamic focusing by implementing the digital delays at the reception, errors occurs due to the above-mentioned approximate interpolations, the AD sampling frequency is made high with a high cost, or the low speed beamforming must be performed by implementing the above-mentioned high accuracy digital delays on signals (phase rotation processing).

[0079] As far, for waves such as electromagnetic waves, vibration (mechanical) waves such as acoustic waves (compressible waves), shear waves and surface waves etc., and thermal waves etc., disclosed digital beamforming methods on waves such as reflection and transmission waves, scattering waves (forward and backward scattering etc.), refractions, surface waves, ballistic waves, or waves generated by self-emanating sources are limited to the monostatic SA with no steering, the plane wave transmission including a steering case, and the migration method as mentioned above. Also, except for the monostatic SA, all the digital beamforming methods require approximate interpolations; yielding low accuracies.

[0080] In contrast to these, when using a transmission or reception transducer array device with an arbitrary aperture geometry (the transducer can also be used for both transmission and reception; different waves can be respectively dealt with for the transmission and reception), or when using only the reception transducer for the passive beamforming, regardless the using the transmission and reception focusing or steering, and for the cases where the coordinate systems are different for the transmissions and receptions of beams and the displaying images, an arbitrary beamforming should be realized with a high speed and a high accuracy with no approximate interpolate calculations.

[0081] For the active beamforming, array-type transmission and reception transducer devices with arbitrary aperture geometries are used (one device may be used for both transmission and reception). For the passive beamforming, only an array-type reception transducer device with an arbitrary aperture geometry is used. For the beamforming, arbitrary beamforming is desired to be performed with a high speed and with a high accuracy via digital processing. In practice, arbitrary focusings and arbitrary steerings are desired to be performed using array-type transducer devices with arbitrary aperture geometries.

[0082] After beamforming with phasing and summing, linear or nonlinear signal processing is implemented on plural beams with at least one different wave parameter among a frequency, a bandwidth, a pulse shape, a beam shape etc. in each direction in order to yield a new beam with at least one different wave parameter (in various fashions such as frequency modulation, widebanding, multi-focusing etc.). In beamformings like these, focusing, steering and apodization can be performed via the DAS processing using arbitrary array-type transducer devices with arbitrary aperture geometries.

[0083] Because the propagation speed of a wave is determined by the properties of a medium under physical conditions, when the multidimensional array comprising of 2D or 3D distribution of aperture elements is used for multidimensional space imaging, due to increasing the number of beams and data required for generating one beam, it takes much longer time to complete beamforming. Thus, a real-time processing instrument or an instrument that displays results in a short time should be used by obtaining a high speediness in beamforming.

[0084] As far, regarding digital beamformings using Fourier's transform, mainly the beamformings to be achieved via approximate interpolations on the Cartesian coordinate system using a 1D or 2D linear array-type transducer is disclosed. However, including the cases where coordinate systems are different for transmission, reception and display, digital beamformings are desired to be performed not with approximate interpolations at all.

[0085] Also the methods disclosed for cases where the geometry of an array aperture is not flat (for instance, the geometry of an array aperture is an arc) requires approximate interpolations. For instance, as typical cases, for using a convex-type transducer, an electric or mechanical sector scan or an IVUS scan (intravascular ultrasound), beamformed data are required to be generated directly on arbitrary display coordinate systems such as the Cartesian coordinate system by implementing digital processings on signals received on arbitrary coordinate systems such as the polar coordinate system.

[0086] Although recently a memory and an AD convertor became remarkably cheap, by sampling a wave on the basis of the Nyquist theorem, however, without over-sampling of data, the beamforming is desired to be completed with a higher speed than the beamforming with the DAS processing. The apodization is also required to be performed properly.

[0087] By solving these problems, it is desired to achieve a high spatial resolution and a high contrast including the effects of suppressing sidelobes in image signals obtained in a real-time or in a short time. Moreover, it is desired to achieve high accuracy measurements of target's motion (displacement) or deformation, or temperature etc. from the obtained signals. For instance, recently in a medical ultrasound field, after measuring a tissue displacement or velocity by applying the Doppler method to echo signals, by applying temporal or spatial derivatives to these measurements, a tissue acceleration or strain etc. is calculated and displayed. Since the temporal or spatial derivative is a processing that amplifies high frequency measurement errors and decreases an SNR (Signal-to-Noise ratio), the displacement measurement accuracy must be made high by using the signal phase. As far, as the high accuracy beamforming, the dynamic focusing on the basis of the so-called DAS processing was used. The 3D imaging instrument using a 2D or 3D array tends to spread. Thus, it is desired to achieve arbitrary beamformings including the dynamic focusing with high speeds and high accuracies without approximate interpolations.

[0088] Recently, the present inventor realized high accuracy measurement methods of a rather high speed tissue motion or shear wave propagation on the basis of high speed beamformings using steered plane wave transmissions (high speed transmission and reception of signals from an ROI). Also for such beamformings with no focusing, it is desired to complete the beamformings with high speeds and high accuracies with no approximate interpolations. By performing high speed beamformings with changing a steering angle and coherent superposition of them, it is made possible to yield almost the same image qualities (a spatial resolution and a contrast) as those of conventional focused beamforming, however, with a higher speed. Such high speed beamformings are also effective for the multidimensional imaging using a multidimensional array.

[0089] Also it is desired to achieve the steering using a classical SA (monostatic type) on the basis of scanning with driving each one transmission element and the multistatic SA with high speeds and high accuracies without approximate interpolations. Also when using so-called migration processing, similarly it is desired to perform arbitrary beamformings on arbitrary coordinate systems with high speeds and high accuracies with no approximate interpolations. Other concrete examples of beamformings to be realized are described in other parts of the present patent document, similarly which are also desired to be performed with high speeds and high accuracies.

[0090] The first purpose of the present invention is that it is made possible, while using instruments with digital operational functions as digital beamformers, to perform arbitrary beamformings with high speeds and high accuracies with no approximate calculations. According to the invention, for instance, the below-described various applications of waves including superresolution imaging using nonlinear processing etc. can be made performable.

[0091] The present invention solves the above-mentioned technical problem at least partially. The beamforming method according to one aspect of the present invention is a method on a Cartesian coordinate system using an axial direction x determined by a direction of a aperture of a flat reception aperture element array and a lateral direction x orthogonal to the axial direction x, in a case where an arbitrary wave is transmitted form a wave source positioned in an arbitrary direction to a measurement object and a wave arrival from the measurement object is processed as a transmission or a reception beamforming is performed with a steering angle θ defined with respect to the axial direction is zero or nonzero degree, and the wave arrival from the measurement object is reception-dynamic-focused with a steering angle φ defined with respect to the axial direction is zero or nonzero degree, and the a beamforming method includes the steps of: (a) where the wave arrival from the measurement object is received at least by a reception aperture element to generate a reception signal; and (b) where beamforming processing is performed at least by implementing Fourier's transform and wavenumber matching with respect to the reception signal generated in step (a), wherein step (b) includes without performing wavenumber matching including approximate interpolation processings in a wavenumber domain or in a frequency domain with respect to the reception signal, and the reception signal is Fourier's transformed in the axial direction y and the calculated Fourier's transform is multiplied to a complex exponential function (101) expressed using a wavenumber k of the wave and a wave number k₀ expressed by a carrier frequency ω₀ as k₀ (=ω₀/c) and imaginary unit i to perform wavenumber matching in the lateral direction x,

exp{i(k sin θ+k₀ sin φ)x},  (101)

and further, the product is Fourier's transformed in the lateral direction x and the calculated result is multiplied to a complex exponential (102), from which an effect of the lateral wavenumber matching is removed, to yield a spatial resolution in the axial direction y and simultaneously multiplied to a complex exponential function (103) as well to perform wavenumber matching in the axial direction y, and the lateral wavenumber is expressed as k_x,

exp(i√{square root over (k²−(k_x−k sin θ−k₀ sin φ)²)}y),  (102)

exp[i{k cos θ+k₀(−1+cos φ)}y],  (103)

by which the wavenumber matching is performed with no approximate interpolations, and an image signal is generated on the Cartesian coordinate system directly.

[0092] The present invention includes instruments and methods that are used for performing arbitrary beamformings on arbitrary coordinate systems with a high speed and a high accuracy, and without approximate calculations required for general digital processings, on the basis of properly using the FFT, the multiplications of complex exponential functions and the Jacobi operation. In order to solve the problem, for waves such as electromagnetic waves, vibration (mechanical) waves such as acoustic waves (compressible waves), shear waves and surface waves etc., and thermal waves etc., proper digital processing algorithms implemented on digital circuits and softwares and analogue and digital hardwares are used for the waves such as reflection and transmission waves, scattering waves (forward and backward scattering etc.), refractions, surface waves, ballistic waves, or waves generated by self-emanating sources, waves transmitted from moving bodies, or waves that arrive from unknown sources etc.

[0093] The hardware includes an instrument that equips an operational function that allows digital wave signal processing as well as a phasing and summing device that is used in a general beamformer of each wave instrument, in which the softwares of the present invention can be implemented, or digital circuits that performing the operations can be used. As mentioned later, other required devices are, at least, transducers, transmitters, receivers, and storage devices of received signals etc., which are used in general. Waves such as harmonic waves can also be dealt with. Beamformings using virtual sources and virtual receives can also be performed. Parallel processing can also be performed for generating plural beams simultaneously.

[0094] The present invention uses analogue devices such as the above-mentioned analogue amplifiers or attenuators for controlling a signal level, analogue filters etc., and effective applications of analogue signal processing devices (linear and specific nonlinear devices for modifying a wave shape by such as enhancing or decreasing of wave properties of a driving signal), and for performing digital processing on stored signals, the above-mentioned devices or calculators, PLDs (Programmable Logic Devices), FPGAs (Field-Programmable Gate Arrays), DSPs (Digital Signal Processors), GPUs (Graphical Processing Units), microprocessors etc. that equip general calculation capabilities, and also special calculators and special digital circuits, or special devices.

[0095] It is important that not only such analogue devices, AD convertors, memories, devices that perform digital signal processing (multi-cores etc.) are high efficient but also the number of communication channels between devices, channel capacities, wirings, wideband wireless communications. In particular, in the present invention, it is desired that such functional devices are installed into a chip or a circuit board (the devices may be detachable), or the devices are directly implemented into a chip or a circuit board (including a multilayer type). Parallel processings are also important. When a calculator also plays a role of a controller unit, if the device is not detachable, a remarkably higher security can be achieved than that obtained under a general programmed control. In a contrary, under the existing legislation, cases where disclosing of processing contents is demanded will increase.

[0096] According to one of viewpoints of the present invention, it is made possible, while using instruments with digital operational functions as digital beamformers, to perform arbitrary beamformings with high speeds and high accuracies with no approximate calculations. As explained later in detail, the present invention realizes, on the basis of proper using of the multiplications of complex exponential functions and the Jacobi operation, arbitrary beamformings on arbitrary orthogonal coordinate systems including a curvilinear coordinate system with high speeds and high accuracies with no approximate interpolations.

[0097] Although the DAS (Delay and Summation) processing realizes arbitrary beamformings including conventional beamformings, when using a 1D array-type physical aperture and a general PC (personal computer), at least the present invention makes the calculation speeds 100 times as high as those achieved using the DAS processing. When the aperture elements distribute in a 2D or 3D space or comprise a multidimensional array, the present invention efficiently solve the problem that it takes more processing times in the multidimensional cases than in the 1D case, i.e., the increasing the speediness of beamforming becomes more efficient.

[0098] That is, the present invention uses a transmission or reception transducer array device with an arbitrary aperture geometry (it may be used for both transmission and reception) or a sensor array device, and allows arbitrary beamformings with high speeds and high accuracies and with no approximate interpolations via digital processing. In practical, arbitrary focusings, arbitrary steerings, arbitrary apodizations can be performed with array devices with arbitrary aperture geometries.

[0099] For instance, in a field of medical ultrasound imaging, according to observation targets, a coordinate system on which physical transmission and reception and digital sampling are performed is selected such as a Cartesian coordinate system for a linear array-type transducer and a polar coordinate system popular for a convex type transducer, a sector scan, or an IVUS (intravascular ultrasound). For instance, for observing a heart dynamics between ribs, the sector scan is performed generally. An aperture of not a transducer with an array-type aperture geometry but a PVFD (polyvinylidene fluoride) based transducer may be deformable. That is, the present invention allows obtaining signals directly beamformed on arbitrary coordinate systems such as image displays etc. with no approximate interpolations by processing digital signals obtained from waves transmitted and received on arbitrary coordinate systems.

[0100] For the multistatic SA, echo data frames with the number of reception elements are made from echo signals received at a same position within plural reception positions with respect to a transmission position, each of which echo data frame are processed by the monostatic SA of the present invention and finally the IFFT is implemented on the superposition of all the monostatic SA results. That is, echo data can be generated by performing the monostatic SA processings with the same number as that of received channels. Thus, it takes shorter time to complete the beamforming (a higher speed) than the DAS method, known as the general multistatic type method, that yields high spatial resolution image signals by generating low spatial resolution image signals to be superposed.

[0101] And on the basis of the multistatic processing of the present invention, the reception dynamic focusing and steering can also be performed, with respect to the popular fixed transmission focusing, with a high speed and a high accuracy. All the beamformings can be achieved by implementing the proper phase rotation processings using the multiplications of complex exponential functions.

[0102] Also regarding a coordinate system, the present invention also allows, on the basis of performing the Jacobi operation on the Fourier's transform, generating echo data directly on a Cartesian coordinate system used for the display with a high speed and a high accuracy with no approximate interpolations, for instance, for performing the signal processing on the convex or sector scan, IVUS.

[0103] Using the present invention, when using the so-called migration processing, similarly arbitrary beamformings can be performed on arbitrary coordinate systems with high speeds and high accuracies with no approximate interpolations. The present invention also allows the uses of virtual sources for performing high SNR and high spatial resolution imagings with high speeds. Moreover, the present invention also allows with high speeds and high accuracies, on the basis of digital signal processing, frequency modulating and widebanding of beams via linear or nonlinear processing, multi-focusing, parallel processing, virtual sources or receivers etc. The present invention is also effective for optimizing beamformings that require much calculations.

[0104] As mentioned above, regardless performing the transmission and reception focusing, and transmission and reception apodizations or not, the present invention allows, for waves such as electromagnetic waves, vibration (mechanical) waves such as acoustic waves (compressible waves), shear waves, ballistic waves, surface waves etc., thermal waves etc., arbitrary beamformings with high accuracies and high speeds on the basis of digital processings, even if the coordinate systems of transmissions/receptions and generations of beamformed signals are different each other.

[0105] Thus, not only the frame rates for displaying the images of beamformed signals increase but also, regarding image qualities, high spatial resolutions and high contrasts can be yielded. Moreover, using the beamformed signals, measurement accuracies on displacements, deformations, temperatures etc. can also increase. The increase in a processing speediness yields a remarkable effect on the multidimensional imaging using a multidimensional array. The present invention relates to mathematical algorithms regarding wave propagations, which was obtained as products by leading to solutions with no approximate calculations even via performing the digital processings. These cannot be achieved simply.

[0148] Below, embodiments of the present invention will be explained in detail with referring to figures. The same compositions of instruments are referred to using the same codes or numbers by which overlapped explains are omitted. The instruments related to the present invention can be used as a measurement and imaging instrument as well as a communication instrument. Below explained are mainly about generations of image signals of transmission waves, refraction waves, reflection waves, scattering waves (forward and backward scatterings etc.) such as of an acoustic pressure and a particle (medium) velocity for an acoustic wave such as an ultrasound etc., a stress wave or a strain wave for a compressible wave (longitudinal wave) or a shear wave (transverse wave), a ballistic wave, a surface wave etc., an electric field wave or a magnetic wave for an electromagnetic wave, a temperature or a thermal flux for a thermal wave.

[0149] At first, the compositions of the measurement and imaging instrument or the communication instrument related to the first embodiment of the present invention are explained. FIG. 1 shows a schematic representation (block map) of compositions of the measurement and imaging instrument or the communication instrument related to the first embodiment of the present invention. As shown in FIG. 1, the measurement and imaging instrument (or communication instrument) is equipped with a transmission transducer (or an applicator) 10, a reception transducer (or a reception sensor) 20, an instrument body 30, an input device 40, an output device (or a display device) 50, and an external storage (memory) device 60.

[0150] FIG. 2 shows the specific schematic representation (block map) of compositions of a body of instrument shown in FIG. 1. Mainly, the body of instrument 30 is equipped with a transmission unit 31, a reception unit 32, a digital signal processing unit 33 and a control unit 34. Here, the reception unit 32 can include the digital signal processing unit 33. FIG. 1 and FIG. 2 show a properly simplified block map to the last, to which the present embodiment is not limited and the detail of the present embodiment is explain below. For instance, communications between the instruments, or between the units or in units are properly performed on the basis of a wire or wireless technology, and they can also be set at different positions. The body of instrument 30 is conventionally referred to one comprised of such plural units.

[0151] The transmission transducer (or the applicator) 10 shown in FIG. 2 generates and transmits waves using drive signals provided from the transmission unit 31 in the body of instrument 30. On the present embodiment, plural transmission aperture elements 10a of the transmission transducer 10 comprise an array.

[0152] FIG. 3 shows illustrations of configurations of plural transmission aperture elements used in a transmission transducer. FIG. 3(a1) shows plural transmission aperture elements 10a arrayed densely in a 1D array state; FIG. 3(b1) shows plural transmission aperture elements 10a arrayed sparsely in a 1D array state; FIG. 3(a2) shows plural transmission aperture elements 10a arrayed densely in a 2D array state; FIG. 3(b2) shows plural transmission aperture elements 10a arrayed sparsely in a 2D array state; FIG. 3(a3) shows plural transmission aperture elements 10a arrayed densely in a 3D array state; FIG. 3(b3) shows plural transmission aperture elements 10a arrayed sparsely in a 3D array state.

[0153] The respective transmission aperture elements 10a have shapes of a rectangular, a circle, a hexagon or others, and a flat, a concave or a convex etc., and an array is 1D, 2D or 3D state. The directivity of a transmission aperture element 10a is determined by the frequency or bandwidth of a generated wave, and the geometry of transmission aperture element 10a. Generally, the directivity is exhibited in a 2D or 3D space. When the element is comprised of two apertures that respectively have directivities in orthogonal two directions, or three apertures that respectively have directivities in orthogonal three directions, the element can also be counted to be one. Also an element can also be comprised of larger than three apertures that have directivities in larger than three directions. The number of apertures in an element may be different at positions and also they can be mixed in with.

[0154] Although the transmission aperture element 10a can exist spatially densely or sparsely (at far positions), the present embodiment is explained with no distinguish with 1D to 3D array types. According to objects (communication) in which the waves propagate or the observation is performed, the aperture element arrays have various formations such as a linear type (the alignment of elements is flat), a convex type (a convex, an arc alignment), a focus type (a concave, an arc alignment), a circular type (for instance, an IVUS in a medical ultrasound etc.), a spherical type, a convex or concave spherical kernel type, a convex or concave other geometry types etc. The types are not limited to these. Proper driving these aperture element arrays generates the above-mentioned waves that widely spread in a lateral direction such as plane waves, the steering, the synthetic aperture, fixed transmission focusing etc., i.e., a transmission beam or a transmission wave with a wave-front.

[0155] For electric scanning, as mentioned in detail later, in order to a transmission beam or a transmission wave with a wave-front, by using independent drive signals generated by plural transmission channels equipped in the transmission unit 31 shown in FIG. 2, the transmission aperture elements 10a with the same number as that of the drive signals are independently driven. The transmission aperture element array that is used for generating a transmission beam or a transmission wave with a wave-front is referred to as a transmission effective aperture. Otherwise, all the aperture elements are totally referred to as a physical aperture element array, from which the transmission aperture that is realized by the transmission aperture element 10a driven simultaneously is referred to as a transmission subaperture element array or simply a transmission subaperture.

[0156] When the object in which waves propagate (communication object) are large or over a region of interest (ROI) is observed at once, the instrument may have transmission channels with the same number as that of the aperture elements existing in a physical aperture element array, and all the channels may always be used. However, in order to make the instrument cheaper, by translating the transmission subaperture element array by switching the transmission channels electrically, or by performing a mechanical scan with a physical aperture element array, waves can be transmitted to over the ROI with the minimum number of transmission channels. When the object in which waves propagate (communication object) is large or the size of object to be observed is large, both the electric and mechanical scanning can also be performed.

[0157] When performing sector scanning, a spatially fixed aperture element array of the above-mentioned type can be electrically driven to perform the scanning (electric scanning), or the aperture element array itself can be used to perform the mechanically scanning, or both can be performed together. As classical SAs, there are two types using electric scanning in which the respective elements in an aperture element array are individually driven or using mechanical scanning using one aperture element. That is, a transmission aperture array is composed by performing transmissions at different positions. For the electric scanning, the transmission unit 31 is equipped with transmission channels with the same number as that of transmission elements in a physical aperture array and then, the transmission channel number can be decreased by using a switching device and at least one channel is required similarly to the mechanical scanning. For transmitting polarized waves, at least the channel number expressed by the multiplication of the element number to be driven simultaneously and the number of polarized waves is required for the transmission unit 31.

[0158] The reception transducer (or the reception sensor) 20 shown in FIG. 2 can also be used as the transmission transducer 10 or an exclusive reception array-type sensor another one from the transmission transducer 10. Thus, the reception transducer 20 can also be set at a different position from that of the transmission transducer 10. Otherwise, the reception transducer 20 can be one that allows detecting a different type wave from that generated by the transmission transducer 10. Such a reception transducer 20 can be set at the same position as that of the transmission transducer 10 and can also be installed into a body.

[0159] The reception transducer 20 used in the present embodiment has an array comprised of at least one reception aperture element 20a, and the signals received by the respective elements are independently transmitted to the reception unit 32 (FIG. 2) in the body of instrument. The respective reception aperture elements 20a have shapes of a rectangular, a circle, a hexagon or others, and a flat, a concave or a convex etc., and an array is 1D, 2D or 3D state. The directivity of a reception aperture element 20a is determined by the frequency or bandwidth of a received wave, and the geometry of reception aperture element 20a. When the element comprised of plural apertures can also be counted to be one. The number of apertures in such an element may be different at positions and also they can be mixed in with.

[0160] According to objects (communication) in which the waves propagate or the observation is performed, similarly to the transmission transducer 10, the aperture element arrays have various formations such as a linear type (the alignment of elements is flat), a convex type (a convex, an arc alignment), a focus type (a concave, an arc alignment), a circular type (for instance, an IVUS in a medical ultrasound etc.), a spherical type, a convex or concave spherical kernel type, a convex or concave other geometry types etc. The types are not limited to these. Receiving waves using these aperture element arrays, the above-mentioned waves that widely spread in a lateral direction such as plane waves, the steering, the synthetic aperture, fixed transmission focusing, dynamic focusing etc. are performed, i.e., a reception beam or a reception wave with a wave-front is generated.

[0161] The transducer aperture (element) can also spatially exist not densely but sparsely (at far positions); or transmission and reception can also be performed by mechanically scanning the measurement object; or no array-type transducer generally referred to as can also be used to perform almost same processings of received signals; and the present embodiment is explained with no distinguish about them particularly by mentioning mainly about cases using array-type devices. For instance, when radar apertures exist at different positions of lands, the respective apertures can be comprised as arrays or not.

[0162] Not only for radars carried by a satellite or an airborne but also a transducer to be used for performing mechanical scanning of a measurement target, also in such cases, the transducers can also have an array or not; transmissions and receptions of signals can also be performed at spatially continuously or densely, or at far positions or sparsely. Thus, not only the classical SAs (transmission from one element) but also receptions of signals with respect to transmission beamformings are performed. The aperture element can exist in a 1D, 2D or 3D state. In addition to electric scanning, mechanical scanning can also be performed together.

[0163] Regarding with the electric scanning, as mentioned later, in order to realize a reception beam or a received wave with a generated wave-front, received signals can be detected simultaneously via aperture elements with the same number as that of reception channels equipped with the reception unit 32 (a reception effective aperture). The reception effective aperture can be different from the transmission effective aperture. Such a reception effective aperture is distinguished with the total aperture elements referred to as the physical aperture element array, and the reception aperture realized by the reception aperture elements 20a simultaneously used is referred to as a reception subaperture element array or only a reception subaperture.

[0164] When the object in which waves propagate (communication object) are large or over a region of interest (ROI) is observed at once, the reception unit 32 may have reception channels with the same number as that of the aperture elements existing in a physical aperture element array, and all the channels may always be used. However, in order to make the instrument cheaper, by translating the reception subaperture element array by switching the reception channels electrically (electric scanning), or by performing a mechanical scan with a physical aperture element array, waves can be received from over the ROI with the minimum number of reception channels.

[0165] When the object in which waves propagate (communication object) is large or the size of object to be observed is large, both the electric and mechanical scanning can also be performed. When performing sector scanning, a spatially fixed aperture element array of the above-mentioned type can be electrically driven to perform the scanning (electric scanning), or the aperture element array itself can be used to perform the mechanically scanning, or both can be performed together. As classical SAs, there are two types using electric scanning in which the respective elements in an aperture element array are individually driven or using mechanical scanning using one aperture element. That is, a transmission aperture array is composed by performing transmissions at different positions. For the electric scanning, the transmission unit 31 is equipped with transmission channels with the same number as that of transmission elements in a physical aperture array and then, the transmission channel number can be decreased by using a switching device and at least one channel is required similarly to the mechanical scanning.

[0166] Alternatively, regarding the reception in the case, in a monostatic type where the receptions are performed by the same elements as those of the active transmission elements, the reception unit 32 is equipped with the reception channels with the same number as that of the transmission channels at least. Alternatively, in a multistatic type where plural elements around the active transmission elements to be used in almost cases, for electric scanning, the reception unit 32 is equipped with reception channels with the same number as that of reception elements in a physical aperture array, whereas both for electric and mechanical scanning, the reception unit 32 is equipped with the reception channels with the same number as that of the elements of a reception effective aperture at least. For receiving polarized waves, at least the channel number expressed by the multiplication of the element number to be used for the receiving simultaneously and the number of polarized waves is required for the reception unit 32.

[0167] Transducers 10 or 20 to be used include various ones that allow generating or receiving arbitrary waves such as electromagnetic waves, lights, mechanical waves, acoustic waves or thermal waves etc. For instance, there are transducers 10 that allow transmitting arbitrary waves to the measurement target and receiving reflected waves or backscattered waves generated in the measurement target (also used as the transducers 20). For instance, when the arbitrary wave is an ultrasound, an ultrasound transducer can be used, which allows transmitting ultrasounds using drive signals provided and generating received signals by receiving ultrasounds. It is well known that according to the applications, ultrasound elements (PZT (Pb (lead) zirconate titanate), PVDF (polyvinylidene fluoride) piezoelectric element etc.) are different as well as the structures of the transducers.

[0168] In the medical applications, for blood flow measurement, a narrowband ultrasound is used historically. First in the world, the inventor of present invention has been realizing to use a wideband echo imaging transducer for measurements of soft tissues' displacement or strain (including static cases), shear wave propagation (speed) etc. Also for HIFU treatment, although a continuous wave can be used, in order to realize a high spatial resolution treatment, the inventor of the present patent has been developing new applicators using devices in a high frequency type or in a wideband type. As one of applications of a high intensity ultrasound, as mentioned above, tissues are stimulated by generating mechanical sources in measurement targets with no thermal effects, for which echo imaging transducer can also be used. In addition to the thermal treatments and generations of mechanical sources, echo imagings can also be performed simultaneously. This is also for using of other wave sources and transducers.

[0169] The digital signal processing unit 33 allows controlling the shear wave propagation direction by superposing plural shear waves generated by respective mechanical sources generated temporally or spatially, by which anisotropies of a visco-shear modulus or a shear wave propagation speed. Because shear waves generated almost simultaneously are superposed physically, after observing the shear waves via ultrasonic displacement measurement, the shear waves can be separated. When the shear waves are not superposed physically, after shear waves generated by respective mechanical sources are observed by analyzing and observing ultrasound signals, the results are superposed in order to calculate regarding the synthesized shear wave (superposed shear waves), the propagation direction, the propagation velocity, the visco-shear modulus in the propagation direction. Alternatively, ultrasounds obtained when the respective mechanical sources are generated are superposed, and the synthesized shear wave (superposed shear waves respectively generated by the respectively mechanical sources) is observed to calculate them similarly. These are also in cases where thermal waves generated by thermal sources are observed to calculate thermal properties. As mentioned below, other various processings are performed.

[0170] It is possible to realize a desired thermal source and a desired mechanical source by performing optimizations of transmission and reception apodizations or delays, and a radiation intensity that control the shapes of a thermal source or a mechanical source, and a sound pressure by detecting a transmission wave or a reflection wave. The wave shapes can also be observed with a high sensitivity using a hydrophone, or the shapes can also be estimated by calculating the autocorrelation functions of the signals detected by sensors etc.; on the basis of such processings, linear or nonlinear optimization is performed. The propagation directions of shear waves and thermal waves can also be optimized. In the respective cases, estimation results of mechanical properties and thermal properties are desired to be used.

[0171] For instance, when using a concave applicator, it is possible to focus at a focus position an ultrasound with a high intensity and thus, a wide bandwidth is yielded in a lateral direction. But, the sound pressure shape has feet growing from the focus position. Then, processings such as filtering, weighting etc. are performed on spectra calculated after receiving reflection or reflection waves to shaping the shape to be an ellipse (nonpatent document 7). The fact that the spectra of waves or beams propagating in the respective directions exist in the same directions in a frequency domain can be used. Consequently, an image quality as well as the accuracy of displacement measurement increases.

[0172] Such processing can also be perform to yield the same effects in cases where beams or waves with new properties that cannot be generated by generation of one wave or one beamforming on the basis of one transmission and one reception (for instance, cases where lateral modulation or increasing a lateral bandwidth is performed by superposing crossed waves or beams, multi-focusing is performed, etc.) are yielded by superposing plural reception signals respectively generated by performing plural transmissions, plural receptions or the both with at least a different wave or beamforming parameter, i.e., one of a transmission focus position when transmission focusing is performed, a plane wave, a cylindrical wave, a spherical wave etc. when transmission focusing is not performed, a steering angle (including zero degree with no steering), using or not of apodization, an F-number, a transmission ultrasound frequency or a transmission bandwidth, a reception frequency or a reception bandwidth, a pulse shape, a beam geometry etc. The superposition can also be performed in a real-time (at the same time with the transmissions and receptions), or regarding with the received signals at the measurement objects' same phase, however, at different times. The respective signals to be superposed can also be reception-beamformed ones, or the superposed raw signals can also be reception-beamformed.

[0173] The received signals obtained from the single wave or beam, or the superposed waves or beams can be weighted in a frequency domain to increase a bandwidth and perform superresolution (increasing a spatial resolution). Also the methods etc. described in the paragraph 0009, the observed waves are multiplied by the conjugate or reciprocal of a frequency response of beam properties as the inversion of beam properties. Alternatively, the conjugate of observed wave or the frequency response can also be implemented (These are detection processings, i.e., the former yields a square of envelope; the later yields autospectra or an autocorrelation function). The beamformed (SA), received signals can also be superresolution-processed, and received signals non-reception-beamformed or not beamformed at all (received signals for SA) can also be beamformed after performing superresolution processings.

[0174] Regarding displacement (vector) measurement, in order to increase the accuracies of displacement components, the frequency in the direction of displacement components can be increased. If increasing a spatial resolution is also required, increasing a bandwidth is also performed. For instance, by increasing the frequency via decreasing low spectra, the displacement measurement accuracy can be increased. The calculation amounts can also be decreased. High accuracy displacement measurement etc. can also be performed by generating over-determined systems via generating plural waves or beams physically or dividing spectra on the basis of signal processing. For performing imaging, envelop detection, square detection or absolute detection is implemented, and by superposing the detected waves or beams, speckles can be decreased and specular reflections can be enhanced.

[0175] Similarly, these processings can be performed in various fields using electromagnetic waves as well as using ultrasound or in the medical field. For instance, audible sounds can be observed using ultrasounds (Doppler effect), acoustic sounds or thermal waves can be observed using electromagnetic waves or lights, or earthquake waves can be observed using such waves. In conjunction, physical properties (distributions) related to the waves can also be observed.

[0176] For a transducer, there are contact and contactless types. Every time, impedance matching is properly performed with respect to each measurement object by putting an impedance matcher such as a gel or water etc. for an ultrasound between the measurement target and the transducer. Such an impedance matcher can also be installed into the transducer in advance (impedance layers for an ultrasound). Thus, impedances of waves are performed properly with respect to measurement targets. A power or a carrier frequency, a bandwidth (wide or narrow ones that determines the axial resolution etc.), a wave shape, a size of element (determining a lateral resolution), a directivity etc. designed on the basis of both the aperture element level and the array capability (detail omitted) are used. As an ultrasonic transducer, there is a combined type using layered PZTs and PVDFs, which is equipped with both a transmission acoustic power and a wideband

[0177] When performing forcedly vibrating using a drive signal, by controlling the drive signal, the generated ultrasound frequency or bandwidth can be adjusted or the ultrasound can be encoded (On reception, a bandwidth is selected from signal with a bandwidth determined by the used transducer using an analogue or digital filter). Occasionally, aperture elements with different properties such as a frequency and a sensitivity etc. can be arrayed. Originally, the ultrasound transducer is a handy type and with a favorable usability. Recently, a non-cable type transducer can be used with a handy body of instrument. For a low frequency sound such as an audible sound, there as a speaker and a microphone. With a viewpoint similarly to the ultrasound, transducers for other waves can be realized and however, they are not limited to the case.

[0178] Alternatively, as a transducer 10, transmission transducers that generate arbitrary waves, and as a transducer 20, reception transducers (sensors) that receive arbitrary waves can be used. In the cases, the transmission transducers allows transmitting arbitrary waves to the measurement targets and the sensors allows receiving reflected or backscattered waves generated in the measurement targets, or transmitted, refracted or forwardly scattered waves etc. in the measurement targets.

[0179] For instance, when the arbitrary wave is a thermal wave, a sunlight or illumination, a metabolism etc. that is a thermal source not made intentionally, and alternatively, an infrared warmer or heater etc. that is rather stationary, or an ultrasound transducer that transmits an ultrasound for heating (that may also be used for generating a mechanical source in the measurement object) or an electromagnetic wave transducer, laser etc. can also be used, which are controlled according to drive signals. For receptions of thermal waves for generating reception signals, an infrared sensor, a pyroelectric sensor, detectors of a microwave or a terahertz wave, a temperature sensor such as an optical fiber, an ultrasound transducer (detection of a temperature change using the dependency of a sound speed and a volume change on a temperature), a magnetic resonance signal detector (detection of a temperature using a chemical shift of magnetic resonance frequency) etc. can be used. For the respective waves, transducers that properly performing the receptions can be used.

[0180] For an optical digital camera or a digital mammography, the Charge-Coupled Device (CCD) technology is used, and an integrated circuit (IC) and a sensor can be installed into one body. The same technology is also used in an ultrasound 2D array, and a real-time 3D imaging can be made possible. For detection of an X-ray, the combination of a scintillator and a photocoupler is used, and observation of the X-ray wave has been able to be made possible. When performing digital sampling of high frequency signals, it is effective to perform analogue detection or modulation as preprocessings, i.e. it is effective to store signals into a memory or storage device (storage media) via AD conversion after reception signals is made the low frequency signals. Otherwise, digital detection can also be performed. These can be installed into one body, a chip or a circuit board together with a transmitter or a receiver.

[0181] Otherwise, for instance, when radars exist at far positions etc., the respective apertures can be comprised of array elements, and there are also other cases. A wide directivity can also be obtained by performing mechanical scanning with various apertures. Apertures can exist spatially continuously or densely, or at far positions or sparsely, or with some regularity such as an equal interval, or with an irregularity under physical limitations. For instance, in sea or building, indoor etc., apertures to be used can be spatially fixed with respect to objects in which waves propagate (communication object) or positions to be observed. Otherwise, the respective apertures can also be used for transmissions and receptions, which can receive waves that are responses with respect to transmission from other apertures as well as the reception apertures themselves. In a medicine or biology, ultrasounds generated by radiating lasers to objects can be observed, referred to as photoacoustics (plural wave transducers can be installed into one body). The present invention allows performing photoacoustics that is realized by combining an ultrasound diagnosis instrument and OCT, for instance, for differentiating an artery and a vein, and measuring the respective blood flow velocity (The superresolutions can also be performed). Otherwise, by applying vibrations or ultrasounds to cancerously diseased parts after performing intravenous injection of magnetic substrates having an affinity for the cancerous diseases, generated electromagnetic waves can also be observed. It is possible to use electromagnetic waves to perform communications with various moving bodies.

[0182] Transducers (arrays) used for passive observations such as earthquakes (seismograph), brain waves (EEG, electroencephalograph), MEGs (magnetoencephalograph), biological neural networks (electrode array), electromagnetic waves (antenna), radars etc. are also various, and they can also be used for observing the wave sources. It is possible to estimate the directions of arriving waves on the basis of spectra analysis (one of past achievements of the present patent's inventor). Moreover, when information regarding propagation times cannot also be obtained (generally, positions of wave sources are calculated using times of observed waves at plural positions), particularly using the instruments of the present invention with plural transducers equipped with different positions or reception effective apertures, positions of wave sources etc. can be calculated geometrically. Even if the waves are not pulsed waves nor burst waves, continuous waves can also be used to observe such wave sources. Via any processings, at once the directions of arriving waves are known, the wave sources can be observed in detail by steering or focusing plural types of beams. In the processings, transmissions are steered and receptions are selectively performed in very probable directions, and the image, spatial resolution, contrast, signal intensity etc. are observed, or the directions of wave sources are specified via spectral analysis. Thus, the transducer used in the instrument of the present invention is used for steering, with which the mechanisms of electric scanning, mechanical scanning, or both scannings can be equipped with.

[0183] As the transducers that allows demonstrating the effectiveness of the present invention, typical transducers being rather familiar with or some special transducers are enumerated and, however, the transducers used or applied in the present patent are not limited to them and include various transducers that allow generating and receiving arbitrary waves such as electromagnetic waves, lights, mechanical vibrations, sound waves, or thermal waves.

[0184] At the same time, the same phase of the observation objects in which waves are propagated (communication object) or conditions being identical or almost identical, other time or other phase, plural beamformings, transmissions or receptions can be performed using each aperture. Similarly, plural beamformings, transmissions or receptions can be performed at a pair of apertures. Similarly, plural beamformings, transmissions or receptions can be performed at respective pairs of apertures. In cases including the cases where plural results of beamformings and receptions are obtained using such apertures, new data can also be generated via linear or nonlinear operations. The reception signals to be processed can be superposed ones originally or processed to be superposed.

[0185] For radars etc. carried by spatially moving bodies such as a satellite or an airborne, the arrays can have an array or not, and mechanical scannings can also be performed to obtain wide directivities. Transmissions and receptions of signals can also be performed at spatially continuously or densely, or at far positions or sparsely, or with some regularity such as an equal interval, or with an irregularity if necessary. The moving bodies are various and also include cars, ships, electric trains, submarines, moving robots etc. Others are circulation goods etc., living things etc., bodies moving regularly or randomly etc. In such cases, mobile communication instruments can be used. RFID (Radio Frequency Identification) tag or IC card etc. can also be used.

[0186] In such cases, reception beamformings can be performed with performing transmission beamformings in addition to classical SA (SA on the basis of transmission of each element). Mechanical scannings can also be performed in a regular fashion or irregularly with performing electric scannings to properly propagate waves in spatially large regions. (communications) or properly observe large regions. Needless to say that using a multidimensional array allows properly propagating waves in spatially large regions (communications) or properly observing large regions (permitting multi-directional steering as well as increasing the size of physical aperture).

[0187] Apertures carried can also be used for both transmission and reception apertures, only transmission apertures, or only reception apertures that receive responses not with respect to the transmissions by the reception apertures themselves but with respect to the transmissions by other apertures. Plural moving bodies can be equipped with apertures. At the same time, the same phase of the observation objects in which waves are propagated (communication object) or conditions being identical or almost identical, other time or other phase, plural beamformings, transmissions or receptions can be performed using each aperture.

[0188] Similarly, plural beamformings, transmissions or receptions can be performed at a pair of apertures. Similarly, plural beamformings, transmissions or receptions can be performed at respective pairs of apertures. In cases including the cases where plural results of beamformings and receptions are obtained using such apertures, new data can also be generated via linear or nonlinear operations. In applications mentioned above, according to the objects in which waves are propagated (communication objects) or observation objects, combinations of the apertures of moving bodies and the fixed apertures can also be used.

[0189] Thus, in the present embodiment, using plural transmission aperture elements 10a and plural reception aperture elements 20a (respective elements can work as both the transmission aperture elements 10a and the reception aperture elements 20a), active beamformings are performed. In the active beamformings, arbitrary beamformings can be performed via digital processing including FFT with high speeds and with no approximate interpolations. In practical, arbitrary focusings and arbitrary steerings can be performed using transducer array devices with arbitrary aperture geometries.

[0190] Since the directions of the faces of respective aperture elements are made much account of, generally orthogonal coordinate systems determined by the geometries of physical aperture element arrays (virtual sources are explained separately) are used. The features of the present invention are to generate signals expressing waves directly on the coordinate systems used for displaying the signals mainly via performing reception digital beamformings with no approximate interpolations; and also to perform the reception beamformings on the coordinate systems used for performing transmission beamformings derivatively. Virtual sources or virtual receptors etc. can also be used, and the beamformings can be performed similarly to using the physical aperture element arrays.

[0191] Next, the transmission unit 31 (FIG. 2) equipped with the bogy of instrument 30 is explained. The transmission unit 31 includes the transmitters 31a with plural transmission channels. The transmission channel number is the number of communication lines that are used for performing one beamforming, to send different drive signals to the respective aperture elements. For instance, as mentioned below, the formations of transmission channels are various. The generated waves on the respective transmission aperture elements 10a have frequencies, bandwidths, wave shapes, and directivities that are determined by the transmission aperture elements 10a and the transmission unit 31.

[0192] Applying impulse signals to the transmission aperture elements 10a generates waves determined by the geometries of the transmission aperture elements 10a (thickness or aperture size and shape) and materials (a single crystal is representative type of ultrasound element), and additionally using drive signals with frequencies, bandwidths and wave shapes (including an encoded case), generated at the transmission unit 31, can also be used for performing forcedly vibrating the transmission aperture elements 10a to control the frequencies, bandwidths, wave shapes and directivities of the waves to be generated. The properties of drive signals to be generated are set as parameters under the control by the control unit 34. Desired parameters can also be set automatically via the control unit 34's distinguishing the transducers set on, and the parameter settings or adjustings can also be performed using the input device 40.

[0193] Generally, in order to perform one beamforming every time, plural aperture elements are excited using drive signals with different delays. That is, the transmission unit 31 is equipped with analogue or digital delay patterns, and for instance, delay patterns that realize transmission focusings or steering directions etc. can be used according to the operator's selection using the input device 40. The patterns can be programmable and according to the purposes, the pattern to be used or selective can also be installed via various media such as CD-ROMs, floppy disks, or MOs etc. After running programs, using the input device 40, the patterns can also be selected interactively, and the delays (patterns) can also be directly input. Otherwise, there various cases including the case where the patterns are set by reading out files in which data are recorded etc. Particularly, when the delays to be used are analogue, the delays can also be changed in an analogue or digital manner, the delay circuit or the delay patterns themselves are exchanged by others or switched to others.

[0194] In the body of instrument 30 (FIG. 2), the command signals are sent to the transmitters 31a with plural channels from the control unit 34 to generate drive signals (including an encoded case) for exciting the corresponding transmission aperture elements 10a. Such command signals can be generated on the basis of the command signals for starting the beamformings for generating one frame. When the transmission delays are digital, for instance, digital delays can be implemented on the respective command signals sent to the plural transmitters 31a using, as the trigger signal, the command signal for the transmission aperture element to be excited first. For implementing the digital delays, digital devices to be used in a digital circuit can also be used.

[0195] Otherwise, after a drive signal generated in the transmitter 31a for exciting an element first is implemented with analogue delays for exciting the respective aperture elements, drive signals are sent to the respective aperture elements. When such analogue delays are used, synchronizations required for using digital circuits are not required, and at least a transmitter 31a can be used to excite transmission aperture elements 10a. Thus, transmission analogue delays can be set at several timings, i.e., in front of, behind or in the transmitters 31a, or in the control unit 34, whereas transmission digital delays can be set at in front of or in the transmitters 31a, or in the control unit 34.

[0196] The delay patterns can also be selected by switching analogue circuits or analogue devices and digital circuits or digital devices, and the delays set on the delay devices can be changed under the controls by the control unit 34 or programmable via installing or setting using inputting etc. Delay devices can also be set in the control unit 34. Moreover, when the control unit 34 is made using a calculator etc. as mentioned below, the control unit 34 can directly output command signals that are delayed under software controls.

[0197] The control unit 34 or digital delay can be realized using devices, calculators, PLD (Programmable Logic Device), FPGA (Field-Programmable Gate Array), DSP (Digital Signal Processor), GPU (Graphical Processing Unit), microprocessor etc. with general calculation capabilities, or an exclusive digital circuit and an exclusive device. The devices are desired to exhibit high performance (multi-cores etc.), and also devices used for analogue devices, AD convertors 32b, memories 32c and/or digital signal processing unit 33 performing transmission or reception beamforming processings.

[0198] Important are the number of communication channels between devices, channel capacities, wirings, wideband wireless communications. In particular, in the present invention, it is desirable that such functional devices are installed into a chip or a circuit board (the devices may be detachable), or the devices are directly implemented into a chip or a circuit board (including a multilayer type). Parallel processings are also important. When the calculator also plays a role of the controller unit 34, if the device is not detachable, a remarkably higher security can be achieved than that obtained under a general programmed control. In a contrary, under the existing legislation, cases where disclosing of processing contents is demanded will increase.

[0199] The control software or delays can also be directly encoded, input or installed. The ways how to implementing digital delays are not limited to these. When implementing digital delays for transmission delays, being different from implementing analogue delays, errors determined by the clock frequency for generating the digital control signals occurs; thus in the viewpoints of an accuracy, the analogue delay had better be implemented for the transmission delays. Basically, the errors can be reduced by using a high clock frequency with a high cost. Alternatively, the analogue delays can also be changed in an analogue manner, the delay can also be programmable and the digital control can be made possible. However, the analogue processing has a lower degree of freedom than the digital delay processing, and if the cost is required to decrease, the delay pattern realized using an analogue circuit can also be switched.

[0200] Transmission apodizations are performed using energies of drive signals provided to the respective aperture elements, or temporal changes of magnitudes, i.e., temporal changes in wave shapes (including an encoded case). On the basis of calibration data regarding the aperture elements' conversion efficiencies from the drive signals to waves, the drive signals are controlled. For other purposes such as calibrations, adjustments of the drive signals can also be performed. The command signals from the control unit 34 to the transmitters 31a can be signals that express, as temporal series, the information of wave shapes or phases of drive signals to be generated by the transmitters 31a, encoded signals which the transmitters 31a recognize to generate pre-determined drive signals, or only signals that convey commands to the transmitter 31 that generate pre-determined drive signals with respect to the respective aperture elements existing in an effective aperture.

[0201] Similarly to the delay setting, the transmitters 31a can be programmable such that pre-determined drive signals are generated with respect to the respective aperture elements in an effective aperture, and various formations can be generated. To generate drive signals, an electric power supplier or an amplifier can be used; electric power suppliers that can provide different electric powers or energies, or amplifiers with different amplification degrees can be switched or simultaneously used to generate a drive signal. Similarly to the transmission delay patterns, as mentioned above, the transmission apodizations are directly set or programmable. The delays and apodizations can be implemented in the transmission unit, which are realized at the same hierarchy level or at different hierarchy levels, and in the same or different formations.

[0202] The transmission channels used for driving aperture elements in an transmission effective aperture are switched using switching devices such as a shift-register, a multiplexer etc., beamformings can be performed using other positioned effective apertures to scan the ROI. The delays of delay elements can also be changeable, the delay pattern (delay elements) can also be switched. Moreover, steering in plural directions can also be performed using an effective aperture, and occasionally the aperture position or the effective aperture width can also be changed. Moreover, steering directions can also be changed.

[0203] When switching high voltage signals, exclusive switching devices can be used. Apodizations set on apodization elements can be changeable in a temporal transmission direction or an array direction of aperture elements, or apodization patterns (apodization elements) can be switched on. Being dependent on the aperture position, range direction, or steering direction, the beam geometry can be controlled. Specifically, an apodization (value), zero, means the corresponding transmission element is not active and off. Thus, the apodization can also work as a switch of effective element, and can also determine the effective aperture width (when apodization function in the aperture element array direction is a rectangular window, the switches of the effective elements are on; and when the apodization function is not constant, the switches are weighted on).

[0204] Regarding the delay pattern or apodization pattern, the body of instrument 30 can be equipped with plural patterns, or can be programmable. Then, on the basis of the responses from the object or the results of beamformings performed by the reception unit 32 explained next, the digital signal processing unit 33 (FIG. 2), explained later, in the body of instrument 30 calculates waves' attenuations, scatterings (forward or back scatterings etc.), transmissions, reflections, refractions or sound's frequency variances or spatial distributions etc., optimizations regarding the delays or intensities of waves transmitted from the respective apertures, steering directions of beams or wave-fronts, apodization patterns etc. can be performed.

[0205] For classical SA, there are monostatic and multistatic types performed using transmissions from respective aperture elements (i.e., each 1 element), the active transmission aperture elements 10a are switched or switched using apodizations as mentioned above. There is a case where all the transmission elements are equipped with transmission channels including transmitters 31a. For SAs, it is required to generate waves with sufficient intensities or energies, and the transmission apodization functions are not always important themselves. In practical, generally, SAs are performed simultaneously with reception apodizations using the phasing and summation device. In the present invention, the digital signal processing unit 33 often performs SAs together with the reception apodization. Representative transmission units used in the present embodiment are above-explained, all allowing transmission beamforming can be arbitrarily used and they are not limited to the units above-explained.

[0206] Explained next is about the reception unit 32 and the digital signal processing unit 33 (FIG. 2) equipped with the body of instrument 30. The reception unit 32 includes the receivers 32a with plural channels, AD convertors 32b, and memories (or storage devices, storage media) 32c. The frequencies, bandwidths, wave shapes, directivities of the received signals generated by the respective reception elements are determined by the reception aperture elements 20a and reception unit 32. Arriving of waves to the reception aperture elements 20a generates the reception signals determined by the geometries of the reception aperture elements 20a (thickness or aperture size and shape) and materials (a single crystal is representative type of ultrasound element), and additionally performing filtering processings (analogue amplifiers can also work as the filters), the frequencies, bandwidths, wave shapes and directivities of the received signals to be generated are controlled. The properties of received signals to be generated are set on the basis of filter parameters (frequency properties such as a frequency, a bandwidth) under the control by the control unit 34. Desired parameters can also be set automatically via the control unit 34's distinguishing the transducers set on, and the parameter settings or adjustings can also be performed using the input device 40.

[0207] The general digital reception unit or digital reception device are equipped with the phasing and summing function in addition to like these functions. That is, the DAS processings performed in the digital reception unit or digital reception device perform phasing processings on plural reception signals and also sum the plural phased reception signals. As the phasing processings, the respective reception channels for plural reception apertures implement the AD conversions on the received signals and store the digitized signals in memories, storage devices or storage media etc. that can be written and read out in high speeds basically. In order to perform the phasings at the respective positions of interest in an ROI, reception delays can be implemented on the received signals read out from the storages with high speeds with approximate interpolations in a spatial domain. Otherwise, the reception delays can also be implemented on the received signals read out from the storages, with high accuracies on the basis of the Nyquist theorem, by performing the phase rotations with multiplications of complex exponential functions (the present inventor's past invention), however, it takes much time to complete the processings. The respective signals received by reception apertures can be stored in the positions (addresses) in storages according to the reception delays, and the received signals can be read out and summed, or summed after performing the above-mentioned processings as well.

[0208] FIG. 4 shows illustrations of compositions of the reception unit or reception device including the phasing and summing device that realizes the phasing and summing processings, and the peripheral devices. FIG. 4 shows the reception unit (or the reception device) 35 which is equipped with the phasing and summing device 35d that performs the phasing and summing processings, and other data generation device 35e that implements the digital signal processings on generated image signals, in addition to the receivers 35a with plural reception channels, AD convertors 35b and memories (or storage devices or storage media) 35c. For instance, “other data generation device 35e” generates image display data, and via high order calculations, for instance, “other data generation device 35e” performs the measurements of displacements on the basis of the Doppler method or temperatures, and performs analyses about the object.

[0209] By performing the phasing and summing processings at the respective positions in an ROI, the dynamic focusing is performed. Originally, the dynamic focusing is a term that is used for the range direction with respect to the reception by an effective aperture. In practical, however, the reception digital beamformings performed by the present invention are not limited to this. The reception unit 32 used in the embodiment of the present invention shown in FIG. 2 allows performing high accuracy digital beamformings with high speeds and with no approximate processings, calculation processes of which DAS processings are different from the above-mentioned calculation processes which the term expresses. Thus, in the embodiment of the present invention, the digital signal processing unit 33 shown in FIG. 2 is used instead of the phasing and summing device 35d shown in FIG. 4. In the digital signal processing unit 33, the above-mentioned various other data can be generated on the basis of the image signals.

[0210] The general phasing and summing device can also be realized in the digital signal processing unit 33 used in the embodiment of the present invention. Particularly, the features of the reception unit 32 are that in order to realize high speed and high accuracy processings, preserving the signal intensities or reducing the noises is performed using analogue devices such as analogue amplifiers or attenuators, for signal level controls, of the received signals generated by the reception aperture elements 20a or analogue filters (programmable and works under frequency properties and parameters set via the control unit 34) etc. In addition, by considering an advantage that analogue signal processings are faster than digital signal processings, effective uses of devices for linear or particularly, nonlinear single processings, if required, are also features. The analogue signals obtained through such processings are digitized (AD-converted) and the generated digital signals are stored into memories (or memory devices, memory media) 32c that can be written or read out with high speeds.

[0211] The digital signal processing unit 33 equipped with can be realized using devices, calculators, PLD (Programmable Logic Device), FPGA (Field-Programmable Gate Array), DSP (Digital Signal Processor), GPU (Graphical Processing Unit), microprocessor etc. with general calculation capabilities, or an exclusive calculator, an exclusive digital circuit and an exclusive device, and the digital wave signal processings of the present invention are performed on the stored digital signals.

[0212] The devices are desired to exhibit high performances, and also devices used for analogue devices, AD convertors 32b, memories (or stored devices, stored media) 32c, and digital signal processing unit 33 (multi-cores etc.). Also important are the number of communication channels between devices, channel capacities, wirings, wideband wireless communications. In particular, in the present invention, it is desirable that such functional devices are installed into a chip or a circuit board (the devices may be detachable), or the devices are directly implemented into a chip or a circuit board (including a multilayer type). Parallel processings are also important.

[0213] When the calculator also plays a role of the controller unit 34, if the device is not detachable, a remarkably higher security can be achieved than that obtained under a general programmed control. In a contrary, under the existing legislation, cases where disclosing of processing contents is demanded will increase. The digital signal processing unit 33 can also work as the control unit 34 that controls other units by sending command signals.

[0214] In the reception unit 32 used in the present invention, the trigger signals for making the AD convertors 32b to start the samplings of the received signals generated by the reception transducer (or the reception sensor) 20 (i.e., command signals for starting the AD conversions and storings of the digital signals into memories, stored devices or stored media 32c) are the same as those used for a general reception unit. For instance, ones of the command signals, generated by the control unit 34, for making the transmitters 31 to generate transmission signals to the transmission aperture elements 10a to be excited, can be used. When performing receiving waves suing plural reception aperture elements 20a in an effective aperture, the command signal to be sent to the transmission element to be excited first, last or other elements can be used, and occasionally the predetermined digital delays can be implemented on the trigger signals for staring the AD conversions.

[0215] The command signals can be generated on the basis of a command signal used for starting beamformings for a frame. In other words, the generations of the transmission trigger signals are counted, and if the hardware or control program confirms that the counted number reaches to the predetermined number, or the number, to be a programmable parameter, set by inputting using the input device 40 etc., a command signal is generated to start beamformings for the next frame. Similarly to other parameters, the number can be installed via various media such as CD-ROMs, floppy disks, MOs etc. After running programs, using the input device 40, the number can also be selected interactively, and numeric data can also be directly input. Otherwise, there various cases including the case where the number is set by reading out files in which data are recorded etc. The number can also be set using dipswitches etc. Not so many reception delay patterns are not required, analogue delay patterns can also be implemented on the received signals, after which AD conversions can be performed on the delayed, received signals.

[0216] In order to perform the reception dynamic focusing with high speeds, performing not the present patent's inventor's past invention that multiplications of complex exponential functions are performed on signals in a frequency domain on the basis of the Nyquist theorem but general high speed implementations of reception delays leads to errors determined by the sampling interval of an AD convertor. Thus, the AD converter's (32b's) sampling frequency is made high with a high cost, or the low speed beamforming must be performed by implementing the high accuracy digital delays on signals (phase rotation processing). In contrast, the present invention allows that the received signals are digital-sampled with synchronizations as mentioned above, such types of approximate errors do not occur. Moreover, high speed reception digital beamformings can be performed. The reception digital beamformings are remarkably faster than the present patent's inventor's past invention that performs the multiplications of the complex exponential functions in a frequency domain.

[0217] In the present patent, and also generally, the reception channel number is the number of communication lines that are used for performing one beamforming, to send waves (signals) received by the respective reception aperture elements 20a to the reception unit 32. Thus, the reception unit 32 can be explained as below.

[0218] The formations of reception channels are various. Generally, in order to perform one beamforming every time, received signals generated by plural reception aperture elements 20a are applied with different delays. That is, the reception unit 32 is equipped with analogue or digital delay patterns as mentioned above, and the delay patterns that realize reception focusings or steering directions etc. can be used according to the operator's selection using the input device 40.

[0219] The patterns can be programmable and according to the purposes, the pattern to be used or selective can also be installed via various media such as CD-ROMs, floppy disks, or MOs etc. After running programs, using the input device 40, the patterns can also be selected interactively, and the delays (patterns) can also be directly input. Otherwise, there various cases including the case where the patterns are set by reading out files in which data are recorded etc. Particularly, when the delays to be used are analogue, the delays can also be changed in an analogue or digital manner, the delay circuit or the delay patterns themselves are exchanged by others or switched to others.

[0220] When the reception delay is digital, the received signals stored in the memories (or storage devices, storage media) 32c are read out to perform the phasing and summing the signals. In the instrument of the embodiment, the digital signal processing unit can implement the reception delays on the digital received signals, the digital received signals can be passed into the delay devices of digital circuit, or the control signals for starting the acquisitions of received signals generated by the control unit 34 (i.e., signals for switching on AD convertors 32b and memories, storage devices, or storage media 32c) can be delayed. Thus, the digital delays can be implemented at arbitrary positions including the AD convertors 32b and the post-devices, or the control unit 34.

[0221] Also the analogue delays can also be implemented on the received signals at arbitrary positions following the generating of the received signals at the reception aperture elements 20a, or at the control unit 34. When using the analogue delay patterns, plural aperture elements' generated received signals can be received at least by one receiver 32a. Thus, in the storages of the received signals, the respective received signals of reception apertures can be stored at positions (addresses) according to the reception delays, or when the received signals cannot be delayed at all, the stored received signals are read out and the digital wave signal processings mentioned later can be performed by the digital signal processing unit 33 (the digital signal processing unit 33 can also perform general phasing and summing processings).

[0222] The delay patterns can also be selected by switching analogue circuits or analogue devices and digital circuits or digital devices, and the delays set on the delay devices can be changed under the controls by the control unit 34 or programmable via installing or setting using inputting etc. Delay devices can also be set in the control unit 34. Moreover, when the control unit 34 is made using a calculator etc. as mentioned above, the control unit 34 can directly output command signals that are delayed under software controls.

[0223] The control unit 34 or digital delay can be realized using devices, calculators, PLD (Programmable Logic Device), FPGA (Field-Programmable Gate Array), DSP (Digital Signal Processor), GPU (Graphical Processing Unit), microprocessor etc. with general calculation capabilities, or an exclusive digital circuit and an exclusive device. The devices are desired to exhibit high performance (multi-cores etc.), and also devices used for analogue devices, AD convertors 32b, memories 32c and/or digital signal processing unit 33 performing transmission or reception beamforming processings.

[0224] Important are the number of communication channels between devices, channel capacities, wirings, wideband wireless communications. In particular, in the present invention, it is desirable that such functional devices are installed into a chip or a circuit board (the devices may be detachable), or the devices are directly implemented into a chip or a circuit board (including a multilayer type). Parallel processings are also important. When the calculator also plays a role of the controller unit 34, if the device is not detachable, a remarkably higher security can be achieved than that obtained under a general programmed control. In a contrary, under the existing legislation, cases where disclosing of processing contents is demanded will increase. The control software or delays can also be directly encoded, input or installed. The ways how to implementing digital delays are not limited to these.

[0225] In the present embodiment, on the basis of the above-mentioned trigger signals sent form the control unit (FIG. 2) in the body of instrument 30, the respective trigger signals that are commands for staring the AD conversions are provided to the AD convertors 32b of the respective channels. According to the command signals, the AD conversions of analogue signals of respective channels and the storings of the digitized signals into the memories, storage devices or storage media 32c are started. Till one frame of received signals are stored, with changing the transmission aperture position, the transmission effective aperture width, or the transmission steering directions etc. and every the transmissions of waves or beams, with changing the reception aperture position, the reception effective aperture width or the reception steering directions, the transmission unit 31, the reception unit 32 and the digital signal processing unit 33 iteratively perform the processings from the transmission to the storing under the controls by the control unit 34. Moreover, every one frame of received signals is stored, coherent signals are generated by performing the digital wave signal processing method (digital beamforming method) of the present invention on the received signals.

[0226] Thus, if the instrument of the present invention is equipped with the above-mentioned analogue or digital delays, the delays are not always used directly for the DAS beamformings, the delays can also be used for implementing the delays on the timing for starting AD conversions of the received signals and storings the signals into memories (or storage devices, storage media) 32c to save and effectively use the memories, storage devices or storage media, and shorten the access times. The implementation of reception delays used for the beamformings are mainly the digital wave signal processings performed in the digital signal processing unit 33 absolutely and then, the saving and shortening the access time are very meaningful. When performing the classical SA that does not perform the physical beamformings at the transmissions (for instance, physical processings such as using calculators, exclusive devices etc. that are different form the software beamformings such as using calculators, exclusive devices etc.: the transmission or reception focusings or steerings, or the apodizations etc.), the transmission delays are implemented at the same timing as that for implementing the reception delays by the digital wave signal processings.

[0227] Thus, the reception unit 32 is absolutely equipped with independent devices with respect to the respective reception channels, i.e., analogue or digital delays, the receivers 32a, the AD convertors 32b and memories (or the storage devices, storage media) 32c. If required, level controls using analogue amplifiers or attenuators, filters and other analogue operational devices are equipped with. That is, in the present invention's instrument, when the delays are implemented by using the reception delays, if delays for the beamformings are not implemented, errors dependent on a clock frequency do not occur similarly to the implementation of analogue delays.

[0228] That is, since the transmission digital delays causes the errors determined by the clock frequency absolutely, it is required to use an expensive, high clock frequency for decreasing the errors. However, it is not required for implementing the reception digital delays. By implementing the digital delays for the reception delays, no decreasing the accuracy and a high degree of freedom about the settings of delay patterns can be obtained, and by further using the analogue delays for the transmission delays, a high accuracy can be obtained as well as the required clock can be made low. The analogue delays can also be possible for changing the delays in an analogue fashion, and can also be made programmable and digital controllable. However, the analogue delays have a lower degree of freedom than the digital delays, and for decreasing the cost, the delay patterns implemented by an analogue circuit can be switched and used, or exchangeable with proper ones. If a high degree of freedom is required for the transmission delay patterns, the digital delays must work with a high clock frequency.

[0229] As mentioned below, the coherent signals generated by the present invention's beamformings are referred to as “image signals.” The reception effective aperture elements or their positions are controlled similarly to the transmission effective aperture elements (mentioned later). The digital beamformings are not always performed every one frame reception signals are stored. For instance, every the received signals with the number of hardware's channels or a programmable parameter determined or set by the effective aperture width, other numbers predetermined or input by the input devices 40 etc. are stored, the digital beamformings can also be performed (there exists various means of input as mentioned above). Also image signals partially beamformed can also be synthesized, to generate one frame image signals.

[0230] In the cases, the received signals to be processed at adjacent positions can also be overlapped, and for the synthesizing the received signals, simple superpositions can also be performed (spectra superposed in a frequency domain can also be Inverse Fourier's transformed), properly weighted superposition can also be performed, or simple connections can also be performed. The number of stored reception signals can also be confirmed by counting the trigger signals for storing reception signals (command signals sent from the control unit 34) in a hardware or a control program, and as mentioned above the command signal, generated by the control unit 34 every one frame, for starting the digital wave signal processings for the one frame can also be confirmed similarly, and then the one frame image signals are properly generated.

[0231] The highest frame rate realizable depends on the beamforming formation to be implemented, and basically determined by the wave propagation speed. In practical applications, it is determined by the time required for performing the digital calculations of one frame image signals. Thus, it is useful that the above-mentioned partial generations of image signals are performed in a parallel fashion. As mentioned above, it is also useful to perform the multidirectional synthetic aperture (SA) that the inventor of present invention previously developed, to generate reception beams at plural positions or in plural directions with respect to one transmission beam or to perform multi-focusings. In order to perform such beamformings with high speeds, parallel processings are useful. For all the beamformings, on the basis of the transmissions and receptions mentioned above, after storing the received signals for one frame beamforming or partially, the present invention's digital wave signal processings below-mentioned in detail can be performed. When the image signals cannot be generated in a real-time, the frame rate can also be decreased, or off-line processings can also be performed.

[0232] The reception apodizations performs the weighting on the received signals on the respective reception channels of aperture elements, and can be changeable in a range direction. Although it is not impossible to be changeable in an analogue fashion, it is simple to be changeable in a digital fashion. For almost general reception units, the apodizations are changeable at respective positions or respective range positions etc. at the timings of the phasing and summing, whereas in the instrument of the present invention the apodizations can be performed in the digital signal processing unit 33. Alternatively, it is rare that nonchangeable apodizations are performed, in which the apodizations are performed at the timings of level controls of received signals, generated by aperture elements, by analogue amplifications or attenuations.

[0233] Being different from apodizations, on the basis of calibration data about conversion efficiencies of drive signals to waves, at least the calibrations of signal levels can be performed, and also the apodizations can be simultaneously performed together with the level calibrations. The processings can also be objects, the dynamic ranges of wave shapes of received analogue signals can also be nonlinearly extended or compressed, and other analogue devices such as nonlinear elements etc. can also be used in respective reception channels. Including the amplifiers etc., the analogue devices to be used can be programmable, and the setting methods can be various formations. Similarly to other parameters, they can be directly set using the various types of input devices. Generally, the delays and apodizations can be implemented in the reception unit 32, which are realized at the same hierarchy level or at different hierarchy levels, and in the same or different formations, and then the phasing and summing devices can be used. In the digital signal processing unit 33 of the present invention, they can be carried out with a high degree of freedom.

[0234] The reception channels used for driving aperture elements in a reception effective aperture are switched using switching devices such as a shift-register, a multiplexer etc., beamformings can be performed using other positioned effective apertures to scan the ROI. The delays of delay elements can also be changeable, the delay pattern (delay elements) can also be switched. Moreover, steering in plural directions can also be performed using an effective aperture, and occasionally the aperture position or the effective aperture width can also be changed. Moreover, steering directions can also be changed. Simple memories, storage devices, or storage media can be saved, and the access time can also be shorten. It is effective that the data to be frequently used are stored into small size memories that are simply written and read out.

[0235] In the present invention, the saving and shortening the access time are meaningful. The apodization patterns comprised of apodization elements can also be switched. Depending on the aperture position, the range direction and the steering direction, the beam shape can also be controlled. Specifically, an apodization (value), zero, means the corresponding reception element is not active and off. Thus, the apodization can also work as a switch of effective element, and can also determine the effective aperture width (when apodization function in the aperture element array direction is a rectangular window, the switches of the effective elements are on; and when the apodization function is not constant, the switches are weighted on). Thus, the apodization elements are the same levels as those of switches.

[0236] When the delays or apodization patterns are equipped with plural patterns or programmable, the digital signal processing unit 33 in the body of instrument 30 calculates for waves propagating in media, on the basis of the responses from the transmission objects or the results of beamformings, the attenuations, scatterings (forward scattering or backscattering), transmissions, reflections, refractions or acoustic sound's frequency variances or the spatial distributions etc., and the delays or intensities of waves transmitted from or received by respective apertures, steering directions of beams or waves, or apodization patterns etc. can also be optimized.

[0237] In the classical synthetic aperture (SA), all the reception elements can be equipped with the reception channels including the receivers 32a. Generally, SA can be performed, in the phasing and summing device, together with the reception apodizations, and in the present invention, SA can be implemented, in the digital signal processing unit 33, together with the reception apodizations.

[0238] The parameters used in the transmission unit 31 or reception unit 32 mentioned above can effective by installing the parameters into respective functional devices in the units via various media such as CD-ROMs, DVDs, floppy disks, or MOs etc., i.e., an ultrasound frequency, a bandwidth, a code, a delay pattern, an apodization pattern, an analogue device used for the signal processing, an effective aperture, a focus position, a steering angle, and times to perform the transmissions and receptions required.

[0239] After running programs, using the input device 40, the number can also be selected interactively, and numeric data can also be directly input. Otherwise, there various cases including the case where the number is set by reading out files in which data are recorded etc. The number can also be set using dipswitches etc. The units can also be exchanged or switched. By selecting the measurement objects, or setting the transducers on the instrument, the instrument can recognize them and can automatically operate under the desired parameters. It is possible to post-control the parameters. In addition, by installing the functional devices of a general reception unit, the comparison between the image signals obtained using the present invention's instrument and those obtained using the general phasings and summings, particularly including approximate interpolations, can be performed.

[0240] The input devices 40 are used, for instance, for setting various types of parameters as mentioned above. The input devices are various devices such as a keyboard, a mouse, buttons, panel switches, a touch command screen, a footswitch or a tacking ball etc., and not limited to these. Using storage media such as general memories, USB memories, hard disks, flexible disks, CD-ROMs, DVD-ROMs, floppy disks or MOs etc., the operation system (OS) or the device software can be installed or versioned up, various types of parameters can be set up or updated. The input devices 40 are equipped with various types of devices that can read out data from the storage media, or the input devices 40 are equipped with interfaces such that various type devices are installed to be used, if required.

[0241] The input device 40 can be used for setting the parameters of various types of operational modes related to the present embodiment as well as controlling and switching of the operational modes. When the operator is a human, the input device 40 is a so-called man-machine interface, and however the input device 40 is not always controlled by a human. The same inputting operation can also be achieved by receiving the parameters, data, or control signals from other devices via various types of communication standards and connectors, or by using wire or wireless communication (at least communication devices equipped with reception functions) and not limited to the above-mentioned examples. Exclusive or general networks can be used.

[0242] The input data are stored into the internal or external memories with respect to the instrument, stored devices, or stored media, and the functional devices equipped in the instrument operate with referring to the stored data. Otherwise, when the functional devices in the instrument are equipped with the exclusive memories, the data are written into the memories or updated to determine the operational setting in a software fashion, or set or updated in a hardware fashion. Operation of the calculation function considers the resource of the instrument occasionally on the basis of the input data, and the optimized setting parameters can be calculated to be used. The operation modes can also be set by commands. Additional information about the waves of measurement objects (kinds, features and properties of waves, intensities, frequencies, bandwidths or codes etc.) or objects or media in which waves propagate (propagation velocities, physical properties related to waves, attenuations, forward scatterings, backward scatterings, transmissions, reflections, refractions etc. or their frequency variances etc.) are given, the instrument can also perform analogue or digital processings properly.

[0243] <Output Devices>

[0244] As a representative output device 50 is a display device, which can display the generated image signals, and others such as various results measured on the basis of the image signals as numeric data or images etc. The image signals can be converted to display images, or dynamic images or static images in formats (scan converted) and graphic-accelerators can be also used. The images are displayed in a gray (brightness) or color scale, and the means of the brightness or color can be displayed with a scale or a logo. Otherwise, the results can also be displayed using a bird′-eye view, graphs, and not limited to these.

[0245] When the results are displayed, the respective operation modes and various types of parameters or patterns (patterns' names) can also be displayed simultaneously using logos and characters. Also complementary information or various types of data about the measurement objects input by operators or other instruments can be displayed. The display instrument can also be used for displaying the GUI (Graphical User Interface) to be used for setting the respective parameters or patterns using the input instrument 40, or by using an attach command screen, drawn images of arbitrary positions or of arbitrary areas specified can be extended to be displayed largely, and can be used to display the respective numeric data for partially working as an input device 40.

[0246] As the display devices, various ones such as a CRT, a liquid crystal or an LED can be used. Exclusive 3D display devices etc. can also be used etc., and not limited to these. The output data are not always interpreted or read directly, and the body of instrument (calculator) interprets, on the basis of the predetermined calibration data or calculations, the output data and displays the results (for instance, the measurement objects' compositions and structures are understood form the spectral analysis of received signals etc.). The output data can also be output on other instruments, of which output data can also be interpreted. Moreover, the same instruments (for instance, robots etc.) or other instruments can put the output data to practical use.

[0247] One instrument can receive plural waves and can generate image signals, and further the data mining or unification (fusion) etc. can also be performed. Other instruments can also be used to perform processings of the kind. The properties or features of generated image signals (intensities, frequencies, bandwidths, or codes etc.) can also be analyzed. Thus, the data acquired by the instruments related to the present embodiment can also be used in other instruments, and in practical the communication instruments with a transmission function at least can also be used as one of the output devices 50. Exclusive or general networks can also be used.

[0248] The generated image signals or the various results (numeric data or images etc.) measured on the basis of image signals are stored into internal or external memories with respect to the instruments, storage instruments or storage media that can become the out devices 50. Here, these are distinguished with the display devices, and referred to as “storage devices.” In FIG. 2 etc., the external storage device 60 is also shown. When storing the image signals, the operation modes or parameters set, complementary information or various types of data about the measurement objects input by operators or other instruments can be stored together with the image signals. As the storage devices, general or special memories, USB memories, hard disks, flexible disks, CD-R (W), DVD-R (W), a video recorder, or image data storage devices etc. can be used, and not limited to these. The storage devices are properly used according to the applications, data amount to be stored or times required for writing in or reading out etc.

[0249] Past stored image signals or other data are read out from the storage devices and replayed. The storage devices are important in that an OS or a device software, or parameters set are stored mainly. The respective functional devices can also be equipped with exclusive storage devices. Detachable storage devices can also be used in other instruments.

[0250] The body of instrument 30 reads out image signals stored in the storage devices and implements the high order digital signal processings. Resynthesized image signals (frequency modulations, increasing bandwidths or multi-focusings etc.

[0251] performed by linear or nonlinear processings) can be generated, image analyses of image signals (superresolutions, enhancings, smoothings, separations, extractings, or CGs etc.) can be performed, various types of measurements such as displacements and deformations of objects or other various temporal changes etc. can be performed; and images or measurement results can be output and can also be displayed onto display devices.

[0252] The measurement results to be stored include the wave's attenuations, scatterings (forward scatterings, backscatterings etc.), transmissions, reflections, refractions. The stored results are read out and used to optimize various types of parameters for generating image signals. Thus, the storing results can be used. The optimizations can be performed using the calculation functions equipped with the control unit 34 or the digital signal processing unit 33.

[0253] The control unit 34 controls all the operations of the instrument. The control unit 34 can be comprised of various types of calculators or exclusive digital circuits etc., and can work as the digital signal processing unit 33. Basically, according to various types of demands input via the input device 40, the control unit 34 controls, on the basis of various types of control programs or various types of data read out from the storage devices, the transmission unit 31, the reception unit 32 and the digital signal processing unit 33 such that the image signals are generated by performing the transmissions and receptions of waves and performing the wave digital signal processings.

[0254] When the control unit 34 is comprised of the exclusive digital circuits, the parameters can be changeable and however, only the determined operations can be realized even including the cases where the operations are switched. When the control unit 34 uses the calculators, including performing the version up, the degree of freedom is high. In addition to the controls for the realizing the above-mentioned various types of operations, the basis of the control unit 34 is to perform the controls of scannings and image signal generations by providing a repetition frequency or information about the transmission and reception positions etc. to the transmission unit 31 and the reception unit 32 according to the transmission and reception aperture number to be used (the respective channels) or the beam number to be generated, the frame number to be generated (the operations may be continued unless the number is not set or not stopped), the frame rate to be realized. Various interfaces are equipped with and various devices can also be used simultaneously.

[0255] The instrument related to the present embodiment can be used as one of devices used for general networks or sensor networks etc., and may be controlled by the controller of the network systems or may be used as a controller for controlling locally comprised networks. For the uses, interfaces can also be equipped with.

[0256] Next, effective and fast digital beamforming methods using digital Fourier's transforms, performed by the digital signal processing unit 33 in the body of instrument 30, for plural transmission and reception aperture elements (including arrayed elements) are explained. In the digital signal processings, occasionally, the middle of data generated in the calculation process or data to be iteratively used can be stored into the memories equipped with or storage devices. For generating plural image signals with the same phases of the objects, the storage devices can be used effectively. The small size memories can also be useful.

[0257] The generated image signals can also be displayed as a static image by the output device 50 such as a display device etc., or can also be stored into the external storage devices 60 using storage media such as hard disks etc. When the digital signal processing unit 33 is a calculator, various programming languages can be used. Although the assembler is useful, when the calculator is run using high-level language programs such as C-language or Fortran etc., high speed operations can also be performed by implementing the optimizations or parallel processings at the compiling the languages. Softwares for performing general operations such as MatLab or various types of control softwares, ones with graphic interfaces etc. can also be used, or special ones can also be used.

[0258] Below, by using cases where the waves are ultrasounds, the beamfoming methods for used for the present invention's instruments are explained. The beamforming methods used for the present embodiments are the following methods (1) to (7). On the methods (7), in addition to various types of beamforming methods, the representative observation data generated by the digital signal processing unit 33 are disclosed.

[0259] The method (1) is a method used for the reception beamformings with respect to transmissions and/or receptions of plane waves including cases where the transmission direction is steered, in which wavenumber matching (mapping) is performed in a Fourier's domain with no approximate interpolation required for the past Fourier beamforming methods. The method (1) includes an invention performed on the wavenumber matching when the steering is performed, i.e., performing multiplications of the complex exponential functions related to the respective cosine and sine of a steering angle to received signals to perform the wavenumber matchings in the axial and lateral directions. Similarly to the classical monostatic SA, the accuracies of measurement results are increased. Moreover, the method (2) is also disclosed, i.e., a high speed digital processing method about steered dynamic focusings to be performed on the basis of the monostatic SA.

[0260] Moreover, the method (3) is also disclosed, i.e., a high speed digital processing method on the basis of the multistatic SA. The method (2) performing the digital monostatic SA with steering can be achieved with a high accuracy such that the 1st moments of multidimensional spectra or the instantaneous frequencies of generated image signals can be expressed ideally using the steering angle and the carrier frequency (as mentioned later, a wavenumber vector has components expressed by the multiplications of sine and cosine of the steering angle with respect to the carrier frequency) by performing wavenumber matching with no approximate interpolations similarly to the method (1). Alternatively, the method (3) performing the multistatic SA can be achieved by generating echo data frames, with the same number as that of reception elements, comprised of echo signals received at the same position in plural reception position with respect to the transmission position. Moreover, the above-mentioned monostatic digital SA is implemented on the respective echo data frames in a Fourier domain, and the superposed, processed results are inverse-Fourier transformed to accomplish the multistatic SA with a high accuracy. Consequently, the method (3) can generate echo data with the same number of digital SA processings as that of the reception aperture channels, and with a remarkably higher speed than the so-called conventional DAS (Delay and Summation) method generates a high spatial resolution image signal frame by superposing the generated low spatial resolution image signal frame.

[0261] By the way, the DAS method can be realized by implementing delays (phasing) onto the received signals with a high speed via performing approximate interpolations in a spatial domain or by implementing delays in a Fourier domain (a past achievement of the present invention's inventor), after which the phased, received signals are summed in a spatial domain. The former yields a high speed, but low accuracy, beamforming; the latter yields a high accuracy, but low speed beamforming.

[0262] The method (4) realized on the basis of the method (1) or (3) is also disclosed, i.e., a high accuracy digital dynamic focusing reception beamforming method for a transmission fixed focusing. Moreover, the method (5) is also disclosed, i.e., for allowing the echo data generations using the convex, sector scanning or IVUS, from echo data received on the polar coordinate system, directly on the Cartesian coordinate system used for displaying the echo data to be generated with a high accuracy with no approximate interpolations by performing processing via the Jacobi operation.

[0263] The method (6) is also disclosed, i.e., the migration method using the present inventions that allows high speed processings with high accuracies and with no approximate interpolations. All the beamforming processings of methods (1) to (5) can also be performed by using the migration method. At last, the applications on the basis of these methods (1) to (5) are disclosed as method (7). Using these methods, it is possible to demonstrate that arbitrary beamformings on the basis of focusings and steerings can be performed.

Method (1): Transmission and/or Reception Beamforming of Plane Wave
(i) Echo Signal with Respect to Plane Wave Transmission (Image Signal)

[0264] FIG. 5 shows illustrations for a steered plane wave transmission. The plane wave transmission can be performed using a linear array-type transducer by using all the effective array elements simultaneously to transmit ultrasounds. When the wavenumber is k, and when the plane wave with the wavenumber vector expressed as eq. (0) is transmitted (x and y respectively expresses the orthogonal directions of scanning and an axial (depth) of the Cartesian coordinate system, of which zeros of y-axis exist on the position of reception effective aperture element array), the acoustic pressure of position (x,y) is expressed as eq. (1).

(k_x^t,k_y^t)  (0)

p(x,y;k)=A(k)e^ikxtx+ikyty  (1)

[0265] Here, A(k) is frequency spectra of a transmitted pulse, and eq. (2) holds.

k_y^t=√{square root over (k²−(k_x^t)²)}  (2)

[0266] Each echo signal form a scatter with a reflection coefficient f(x,y_i), positioned at a depth y=y_i, is expressed as eq. (3).

s(x,y_i,k)=f(x,y_i)p(x,y_i,k)  (3)

[0267] The angular spectrum of the eq. (3) is expressed by eq. (4).

$\begin{array}{cc}\begin{array}{c}S\left(k_x,k,y_i\right)={\int }_xs\left(x,y_i,k\right){}^{k_xx}x\\ ={\int }_xf\left(x,y_i\right)A\left(k\right){}^{k_x^tx+k_y^ty_i}{}^{k_xx}x\end{array}& \left(4\right)\end{array}$

[0268] Expressing the frequency response of the transducer by T(k), the angular spectra, at the aperture plane (y=0), of the echo signals from the depth y=y_i are expressed by eq. (5).

$\begin{array}{cc}\begin{array}{c}R\left(k_x,k,y_i\right)=T\left(k\right)S\left(k_x,k,y_i\right){}^{k_yy_i}\\ =T\left(k\right)S\left(k_x,k,y_i\right){}^{\sqrt{k^2-k_x^2}y_i}\end{array}& \left(5\right)\end{array}$

[0269] Thus, adding the angular spectra from the respective depths yields the angular spectra of echo signals expressed by eq. (6).

$\begin{array}{cc}\begin{array}{c}{R}^{\prime }\left(k_x,k\right)={\int }_y^{}R\left(k_x,k,y\right)y\\ ={\int }_{x,y}f\left(x,y\right)A\left(k\right)T\left(k\right){}^{k_x^{{\prime }^{\prime }}x+k_y^{{\prime }^{\prime }}y}xy\end{array}& \left(6\right)\end{array}$

[0270] Thus, the echo signals (image signals) are expressed by eq. (9) by implementing IFFT on the spectra via performing the wavenumber matching expressed by eqs. (7) and (8).

$\begin{array}{cc}F\left(k_x^{\prime },k_y^{\prime }\right)=R^{\prime }\left(k_x,k\right)& \left(7\right)\\ \{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k\sin \theta \end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{k^2-k_x^2}+k\cos \theta \end{array}\end{array}& \left(8\right)\\ f\left(x,y\right)=F^{-1}\left(F\left(k_x^{\prime },k_y^{\prime }\right)\right)& \left(9\right)\end{array}$

[0271] Considering the transmission and reception inversely, arbitrary transmission beamformings (for instance, steered plane wave, steered fixed focusing beam, steering dynamic focusing using SA, non-steered waves or beams, and various others etc.) are performed with respect to the measurement object, a wave arriving from the measurement object can be used as a received plane wave with the steering angle θ (including a case of zero degree). The way how to interpret the transmission and reception was not disclosed. Similarly, when arbitrary waves or beams transmitted with arbitrary steering angles (zero or non-zero degree) are performed, it is possible to receive the waves with the same or different steering angles θ (zero or non-zero degree). Moreover, reception beamformings can be performed on the coordinate system determined by the reception aperture with respect to arbitrary waves transmitted from arbitrary wave sources or arbitrary transmission effective aperture array (for instance, the same one as that of the reception effective aperture array or a different one with an arbitrary geometry and an arbitrary direction, other positioned one from the reception effective aperture or in the same physical aperture etc.).

[0272] When physically performing the plane wave transmission with a steering angle α (including a case of zero degree), implementing the steering with a steering angle θ (including a case of zero degree) in a software fashion yields the transmission of a steered plane wave with a steering angle (α+θ) (finally, generated transmission steering angle is the mean of α and θ). The software steering (steering angle θ) can be performed for reinforcing the physically performed steering (steering angle α) or for realizing a steering of a plane wave transmission in a software fashion purely, or can be interpret that reception steering of a plane wave is performed in a software fashion.

[0273] When performing the transmissions with a physical steering angle α, a software steering angle θ or both steerings α+θ are performed, reception dynamic focusing with a steering angle φ can be realized by performing the steering angle used in the method (2) next explained (finally, generated transmission steering angle is the mean of transmission and reception steering angles) The software steering (steering angle θ) can be performed for reinforcing the physically performed steering (steering angle α) or for realizing a steering of a plane wave transmission in a software fashion purely, or can be interpret that reception steering of a plane wave is performed in a software fashion in addition to the reception dynamic focusing (including a case where the steering angle φ is zero degree).

[0274] In these cases, the software transmission and reception beamformings can be considered inversely. Performing the exchanging of the software steered plane wave transmission (including a case where the steering angle is zero degree) and the software steered dynamic focusing reception (including a case where the steering angle is zero degree) has the same processings as those of the original beamforming (equivalent). Generated, beamformed signals can also be interpreted as ones beamformed with respect to the physically received, steered plane wave. Generally, regardless performing the steering or not, it is not reasonable to physically perform dynamic focusing transmission and however, it is also possible to interpret that a wave is physically received as a steered plane wave.

[0275] Also using this method allows performing arbitrary transmission beamformings (for instance, steered plane wave, steered fixed focusing beam, steering dynamic focusing using SA, non-steered waves or beams, and various others etc.). That is, performing the same processings as those for this plane wave transmission allows dealing with arbitrary waves or beams (for instance, the above mentioned examples etc.) generated by physical beamformings. In other words, even if arbitrary transmissions are performed, reception beamformings (dynamic focusing etc.) can be performed. Particularly when performing plural transmissions, simultaneous processings can be performed. In addition to a transmission steerings (the angles including a case of zero degree), the transmission or reception steerings of a plane wave or a dynamic focused beam can be performed (the angles including a case of zero degree). The finally generated steering angles are means of the transmission and reception angles. Also similarly to the above mentioned beamformings, the transmission and reception can be considered inversely and then, various combinations of beamformings can be performed. The respective transmission and reception beamformings are performed and plane wave processing can also be performed for both the transmission and reception in a software fashion. As explained later, these are also for the 3D beamformings using a 2D array.

[0276] On the basis of the above explained theory, the calculation method disclosed by J.-y. Lu (nonpatent documents 3 and 4) implements, in order to calculate R(k_x,k), the 2D FFT on the received signals with respect to the time and space at first, the wavenumber matching using eq. (7) next, and the 2D IFFT finally (also described in paragraph 0352). The wavenumber matching is performed using approximations such as a linear interpolation or using the most neighborhood data. Thus, to increase the approximation accuracy, over sampling of received signals is required. High order approximate interpolations or a sinc function can also be used. In 3D cases, similarly, 3D FFT and 3D IFFT are performed. One of features of the present intention is to perform the wavenumber matching with no approximate interpolations and however, when the processings are applied to various beamformings as likely disclosed in paragraphs 0190 to 0194, the corresponding approximate interpolations can also be performed to yield approximate solutions with high speeds.

(ii) The Present Invention's Calculation Procedure of Echo Signal (Image Signal) with Respect to Transmission and/or Reception Beamforming of Plane Wave

[0277] The case where the transmission and/or reception of a plane wave with a steering angle θ is explained. Using the present invention, the wavenumber matching is performed as follows: at first, the wavenumber matching is performed in the lateral direction x by multiplying the complex exponential function (eq. (9a)) to the received signal before performing the FFT in the lateral direction (a spatial direction), and subsequently in the depth direction by multiplying the complex exponential function (eq. (9c)) in addition to the complex exponential function (eq. (9b)) with removed the performed lateral matching processing for simultaneously yielding a spatial resolution in the depth direction y. The steering angle θ can be zero degree as well as non-zero degree. This processing is not disclosed in prior art documents.

exp(ik_x^tx)=exp(ik sin θx)  (9a)

exp(i√{square root over (k²−(k_x−k_x^t)²)}y)=exp(i√{square root over (k²(k_x−k sin θ)²)}y)  (9b)

exp(ik_y^ty)=exp(ik cos θy)  (9c)

[0278] FIG. 6 shows the flowchart explaining the digital signal processing for the steered plane wave transmission. The calculation procedure follows. At the step S11, as shown in eq. (10), the received signals are Fourier's transformed with respect to the time t (FFT should be performed):

R′(x,k)=∫r(x,exp(iωt)dt  (10)

where k is a wavenumber expressed using the angular frequency ω and an ultrasound propagation speed c as k=ω/c, form which analytic signals are obtained. Here, although according to the above-explains, the processing is performed using the plus signed kernel of the complex exponential function for the Fourier transform referred to as, according to the usual Fourier's transform, the processing can also be performed using the minus signed kernel of the complex exponential function. Anyway, when the processing to be performed later as the inverse Fourier's transformed referred to as, absolutely a kernel of which sign is inverted is used in the complex exponential function. This is also for other methods (2) to (7).

[0279] Next, at the step S12, the matching processing is performed with respect to the wavenumber k_x for steering by multiplying eq. (11) to eq. (10) and at the step S13, Fourier's transform is performed on the signals in the lateral direction x (FFT should be performed) to yield signals expressed by eq. (12). When performing the multiplication of eq. (10) (the results of FFT performed on time t) and eq. (11) (the complex exponential function), exclusive FFT can also be useful to yield the multiplication results directly.

exp(ik_x^tx)=exp(ik sin θx)  (11)

R′(k_x,k)=∫R(x,k)exp[i(k_x+k sin θ)x]dx  (12)

The results of eq. (12) can also be obtained by performing the calculation of eq. (12) directly.

[0280] This twice Fourier's transforms (2D Fourier's transform) analyze the received signals into plane wave components. The angular spectra of an arbitrary depth position y generated by the respective plane waves can be calculated by shifting the phase via performing of multiplication of eq. (13).

$\begin{array}{cc}\begin{array}{c}B\left(k_x,k,y\right)=\exp \left(\sqrt{k^2-{\left(k_x-k_x^t\right)}^2}y\right)\\ =\exp \left(\sqrt{k^2-{\left(k_x-k\sin \theta \right)}^2}y\right)\end{array}& \left(13\right)\end{array}$

[0281] At the step S14, the matching processing is also performed on the wavenumber k_y by simultaneously multiplying eq. (14).

exp(ik_y^ty)=exp(ik cos θy)  (14)

[0282] At the step S15, the angular spectra of the respective depths y are calculated. That is, by multiplying eq. (15), eq. (16) can be obtained.

B′(k_x,k,y)=exp(i(√{square root over (k²−(k_x−k sin θ)²)}+k cos θ)y)  (15)

R(k_x,k,y)=R′(k_x,k)B′(k_x,k,y)  (16)

[0283] The acoustic pressure field generated at a depth y by the respective plane wave components can be calculated by performing the inverse Fourier's transform (IFFT) on the lateral direction x as eq. (17).

f(x,y,k)=∫R(k_x,k,y)exp(−ik_xx)dx  (17)

Finally, the image signals can be obtained by summing up the plural wavenumber k (or frequency) components.

[0284] Here, the order of integral calculations regarding the wavenumber k (or the frequency) and spatial frequency k_x are exchangeable. Thus, summing up k components of angular spectra at the step S16 and performing the IFFT with respect to the wavenumber k_x at the step S17 can also yield the same image signals at the step 18. In this case, the calculations can be accomplished by one time inverse Fourier's transform at each depth position and then, the high speed calculation can be achieved. This is also for all methods (1) to (6). The wavenumber matching for steering is performed on the basis of eqs. (11) and (14). Being different from the wavenumber matching method performed via approximate interpolations in a Fourier domain (nonpatent documents 3 and 4), since such approximations are not performed, the present invention allows the high accuracy calculation. Physically or mathematically, the wavenumber matching can also be performed at the first Fourier's transforms or at the last inverse Fourier's transforms. These are also for other methods (1) to (6).

[0285] Also when using a 2D aperture element array, arbitrary waves are transmitted from wave sources positioned in arbitrary directions to the measurement object and then, the waves arriving from the measurement object are received as a plane wave and processed by 3D wave digital signal processing, 3D Fourier's transform is performed regarding an axial (or depth, y) and lateral directions (x and z) on the 3D Cartesian orthogonal coordinate system (x,y,z) expressed by an axial direction y determined by the direction of a flat reception aperture element array and lateral directions x and z, for instance. When the steering angle being an angle between the reception direction as a plane wave and the axial direction (y) is expressed using zero or non-zero elevation and azimuth angles, similarly to when performing the 2D wave digital signal processing explained above, the following wavenumber matching is performed on the 3D Fourier's transform R′ (k_x,k,k_z) of the received signals with no approximate interpolations.

$\begin{array}{cc}F\left(k_x^{\prime },k_y^{\prime },k_z^{\prime }\right)=R^{\prime }\left(k_x,k,k_z\right)& \left(7^{\prime }\right)\\ \{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k\sin \theta \cos \varphi \end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{k^2-k_x^2-k_z^2}+k\cos \theta \end{array}\\ \begin{array}{c}{k}_z^{\prime }=k_z+k_z^t\\ =k_z+k\sin \theta \sin \varphi \end{array}\end{array}& \left(8^{\prime }\right)\end{array}$

Similarly to the 2D case, when the processings are applied to various beamformings as likely disclosed in paragraphs 0190 to 0194, according to eqs. (7′) and (8′), the corresponding approximate interpolations can also be performed to yield approximate solutions with high speeds and in the case, the 3D inverse Fourier's transform is performed on F(k_x′,k_y′,k_z′).

[0286] When not implementing the approximate interpolations on the wavenumber matching, at first the wavenumber matching in lateral directions x and z by multiplying the complex exponential function eq. (C21) expressed by the wavenumber k and an imaginary unit i to the Fourier's transforms of the received signals in the axial direction y.

exp{ik sin θ(cos φx+sin φz)}  (C21)

And the wavenumber matching is subsequently performed in the axial direction by multiplying, to the angular spectra obtained by performing Fourier's transforms on the multiplications in the lateral directions x and z (2D Fourier's transform or 2D FFT), the complex exponential function (eq. (C23)) in addition to the complex exponential function (eq. (C22)) with removed the performed lateral matching processings for simultaneously yielding a spatial resolution in the depth direction y. Here, the wavenumbers in the lateral directions are expressed as k_x and k_z.

exp(i√{square root over (k²−(k_x−k sin θ cos φ)²−(k_z−k sin θ sin φ)²)}y)  (C22)

exp(ik cos θy)  (C23)

The performing wavenumber matching with no approximate interpolations allows generating image signals on the Cartesian coordinate system directly. That is, the sound pressure field at each depth y generated by the respective plane waves can be obtained as image signals by performing the 2D IFFT with respect to the lateral directions x and z and summing up the plural wave number k components (or frequency components). Off course, even when the steering angle or either elevation or azimuth degree is zero, the processings can be performed.

[0287] In the above explained calculations, the bandwidth determined by the transmission signals or the SN ratio of the received signals considered is used to set the bandwidth to be processed. For instance, when generating analytic signals on the basis of eq. (10), those with the required band-limited are generated and stored (corresponding to the down-sampling). Although the method or instrument of the present invention does not perform the approximate interpolations when performing the wavenumber matching, the over-sampling of echo signals in the depth and lateral directions also yield the effects for yielding image signals robust to noises contaminated in received echo signals. These are also for other methods (1) to (6).

[0288] On eqs. (13) to (15) or eqs. (C22) and (C23), by setting the position (coordinate) y in a depth direction or the range, the interval of data in the direction, image signals with an arbitrary depth position or depth range, or an arbitrary interval or density in the depth direction can be generated with no approximate interpolations. Regardless performing the down-sampling explained in the paragraph 0206 or not, up-sampling can be performed. The down-sampling is effective within the Nyquist theorem holds. Intentionally, high frequency signal components can also be filtered out (processed to be outside the bandwidth). Regardless performing the down-sampling explained in the paragraph 0206 or not, the down-sampling can be performed within the Nyquist theorem holds. In addition, on the inverse Fourier's transform such as eq. (17) etc., by setting the lateral position (coordinate) x or the range (if required, spatial shifting is performed in an analogue fashion by using the past invention of the present invention's inventor, i.e., the phase rotation via multiplication of a complex exponential function), image signals with an arbitrary lateral position or range can be generated with no approximate interpolations; and also on the inverse Fourier's transform, by making the lateral bandwidth narrower with removed the lateral high frequency components (if required) to make the lateral density of data lower, or by making the lateral bandwidth wider with padded zero spectra in the angular spectra to make the lateral density of data higher, image signals with an arbitrary lateral interval or density can be generated with no approximate interpolations.

[0289] Thus, the image signals can be generated with the desired arbitrary positions, ranges, intervals, densities. That is, image signals with the shorter intervals than the sampling interval of the received signals and the pitch of the reception aperture elements can be generated. Otherwise, coarse intervals of image signals can also be generated in the respective directions (it is cautious that the Nyquist theorem holds). When performing the wavenumber matching with approximate interpolations, however with high accuracies, on the basis of eqs. (7) and (8) or (7′) and (8′), the approximations are required to be performed with proper over-samplings of data in return an increased calculation amount. In the case, being different from in the case where image signals of arbitrary positions can be generated when no approximate interpolations are performed, it is cautious that the number of data to be used for the Fourier's transforms increases. These are also for other methods (1) to (6).

[0290] When a convex-type transducer, a sector scanning or an IVUS being used, waves spread widely in the angle direction θ (cylindrical waves) can also be transmitted or received in the radial direction r on the polar coordinate system (FIG. 7); or virtual sources set behind the apertures with arbitrary geometries being used, the same beamformings (cylindrical waves) can also be performed (see FIGS. 8A(a) to (c), patent document 7 or nonpatent document 8 etc.). In such cases, the above-explained methods can be implemented with the polar orthogonal coordinate system (r,θ) instead of the Cartesian orthogonal coordinate system (x,y) (the depth y and lateral x coordinates are replaced by r and θ, respectively) and image signals can be directly generated on the polar coordinate system (r,θ). These are also for spherical waves expressed on the spherical coordinate system. Also as shown in FIGS. 8B(d) to (f), when using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries as explained above, the beamformings can also be performed similarly to generate, at an arbitrary distance position, the transmission or reception, or both of plane waves. Performing such beamformings is equivalent to make a formation of a virtual linear-type aperture array (or a plane wave) at the distance position and then, setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually. The distance position can be set behind as well as in the front of the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. The virtual linear-type aperture array can also be used not as the virtual sources but the virtual receivers, or both virtual sources and receivers.

[0291] FIG. 7 shows the illustrations of cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) (transmissions or receptions, in a radial (r) direction, of waves widely spread in an angle direction (θ)). FIG. 7(a) shows the cylindrical wave transmission using a convex-type aperture element array; FIG. 7(b) shows the cylindrical wave transmission using a sector-type aperture element array; FIG. 7(c) shows the cylindrical wave transmission using an IVUS (a circular-type) aperture element array. Although FIG. 7b shows an aperture of which geometry is an arc, a flat aperture can also be used for the sector scanning. Also using these apertures, focused beams can also be generated.

[0292] FIG. 8A shows the illustrations of the cylindrical wave transmissions on the polar coordinate system (r, θ) (transmissions of waves, in a radial (r) direction, widely spread in an angle direction (θ)) from virtual sources set behind physical apertures with arbitrary aperture geometries. FIG. 8A(a) shows the cylindrical wave transmission using a linear-type aperture element array; FIG. 8A(b) shows the cylindrical wave transmission using a convex-type aperture element array; FIG. 8A(c) shows the cylindrical wave transmission using an arbitrary aperture element array. Receptions can also be performed similarly. FIGS. 8B(d) to (f) show, when using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries, the beamformings can also be performed to generate, at an arbitrary distance position, the transmission of a plane wave (In the figures, the cases where a convex-type aperture element array is physically used are shown). Setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually (FIG. 8B(d)). The distance position can be set in the front of (FIG. 8B(f)) as well as behind (FIG. 8B(e)) the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. Reception can be also performed similarly. FIG. 8B(g) shows a special case, for instance, a case where physically using a linear-type array transducer, and a cylindrical wave is generated using a virtual source set behind the physical aperture is applied to generate, at an arbitrary distance position, a pane wave widely spread in a lateral direction or a large virtual linear-type array transducer. Reception can also be performed similarly. The virtual linear-type aperture array can also be used not as the virtual sources but the virtual receivers, or both virtual sources and receivers.

[0293] Nonpatent document 6 discloses performing of transmission focusing and similarly, the result can be obtained on the polar coordinate system (r, θ). For instance, a large FOV can be obtained. As another method from that disclosed in the nonpatent document 6, the method (1) is used for the beamformings and obtaining steered beams with steering angles on the polar coordinate system (r,θ) (one of features of the present invention). These are also when using the methods (2) to (4) and (6). For the cases, the polar coordinate system (r,θ) is used instead of the Cartesian coordinate system (x,y) (the axial x and lateral y coordinates are replaced by r and θ coordinates, respectively). However, when performing these beamformings, to obtain the signals at the positions of the discrete Cartesian coordinate system used for the display, interpolations are required to be performed. The interpolations are strictly performed in a Fourier domain by performing the phase rotations via implementing the multiplications of complex exponential functions, however, with consuming long time; or alternatively performed by approximate interpolations with consuming short time, however, with approximate errors. These are also for using the spherical coordinate system.

[0294] Also in these cases where the beamformings are performed on the polar coordinate system, the displacement measurements can also be performed, for instance, measurements of a displacement in the radial (r) or angle (θ) direction or a displacement vector comprised of both the displacements. To obtain the measurement results at the positions of the discrete Cartesian coordinate system used for the display, interpolations are required to be performed. Similarly to the interpolations for the echo signals, the interpolations are strictly performed in a Fourier domain by performing the phase rotations via implementing the multiplications of complex exponential functions, however, with consuming long time; or alternatively performed by approximate interpolations with consuming short time, however, with approximate errors. These are also for using the spherical coordinate system.

[0295] From the results of displacements, a strain (tensor) or a strain rate (tensor), a velocity (vector) or an acceleration (vector) can be calculated via calculating the partial derivatives using differential filterings and further, mechanical properties (for instance, a bulk modulus or a shear modulus (for instance, nonpatent document 7), elastic modulus tensor of an anisotropic media etc.), a temperature etc. can be calculated via numerical operations. When performing the approximate interpolations, the calculations performed on the Cartesian coordinate system with approximations allow shortening the total calculation time in many cases. Alternatively, performing the numerical operations on the polar coordinate system to obtain the results, of which approximations on the Cartesian coordinate system can be performed with small error propagations. That is, the errors generated in the processes after the displacement measurement are led to only due to the approximate interpolations for obtaining final data to be displayed (There is a case where plural data to be displayed can be obtained from same displacement data).

[0296] As mentioned above, after implementing the interpolation processings on the echo signals to express the echo data on the Cartesian coordinate system, the displacement and the subsequent measurements can also be performed. When the approximate processings are performed on the interpolation processings, errors are led to and however, the total calculation time can be shortened. When measurements are performed on the basis of other echo data processings, as mentioned above, such processings can be performed similarly. These are also when the 3D beamformings are performed using a 2D array.

[0297] For all the above-mentioned beamformings, such processings can also be performed using arbitrary orthogonal coordinate systems except for the polar coordinate system.

[0298] Alternatively, in the same way, when performing cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) (transmissions or receptions, in a radial (r) direction, of waves widely spread in an angle direction (e)) using a convex-type transducer or a sector scan, or an IVUS etc. (FIG. 7) and using virtual sources set behind physical apertures with arbitrary aperture geometries (FIGS. 8A(a) to (c)), the methods for generating image signals directly on the Cartesian coordinate system can be explained as the methods (5), (5-1), (5-1′) etc. When using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries as explained above, the beamformings can also be performed similarly to generate, at an arbitrary distance position, the transmission or reception, or both of plane waves (FIGS. 8B (d) to (f)). Performing such beamformings is equivalent to make a formation of a virtual linear-type aperture array (or a plane wave) at the distance position and then, setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually. The distance position can be set in front of as well as behind the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. The virtual linear-type aperture array can also be used not as the virtual sources but the virtual receivers, or both virtual sources and receivers. Alternatively, in the same way, the beamforming methods can be explained as the methods (5), (5-1), (5-1′) etc. In these cases, the imagings of echo signals and displacement measurements etc. can be performed on the same Cartesian coordinate system consistently. These are also for the polar coordinate system. In such cases, it is also possible to transform the echo signals or measurements on the Cartesian coordinate system to those on the polar coordinate system via interpolations. These are also when using 2D arrays for the 3D beamformings. Transmission focusings may also be performed. Alternatively, in the same way,

[0299] For all the above-mentioned beamformings, such processings can also be performed using arbitrary orthogonal coordinate systems except for the polar coordinate system. As mentioned above, the virtual source or the virtual receiver are not always positioned behind the physical aperture and can also be set in front of the aperture. Regardless the geometry of a physical aperture, they can be positioned arbitrarily (patent document 7 or nonpatent document 8). Thus, the present inventions are not limited to these. On the wavenumber matching in these beamformings, approximate solutions can also be calculated with approximate interpolations. All these can be processed similarly using the methods (1) to (7).

[0300] On the present methods (1) to (7), for these received signals, apodizations for the transmission or reception, or the both can be performed at various timings, because the processings are linear. That is, the apodizations can be performed in a hardware fashion when performing the receivings or in a software fashion after performing the receivings. As mentioned above, the apodizations can also be performed at transmissions physically. These are also for the following beamformings.

[0301] It is natural that when performing the beamformings not with respect to the received echo signals but transmission waves, the coordinate y is not the half round trip distance (expressed as ct/2 using the propagation time t) but the distance (ct) from the aperture element on the coordinate system determined by the reception aperture element.

[0302] Next, the cases where synthetic apertures (SAs) are performed. Two types SAs exist, i.e., a monostatic and multistatic types.

[0303] FIG. 9 shows an illustration of a monostatic type SA. For the SA, an ultrasound is transmitted from one element in an array, and echo is received by the element itself. Also for the SA, by performing the wavenumber matching using the procedure shown in FIG. 6, echo signals (image signals) can be calculated.

[0304] Since the monostatic type SA performs the transmission and reception using the same elements, the propagation paths of ultrasounds to scatters at transmissions are same as those of ultrasounds from the scatters at receptions. Therefore, on the Cartesian coordinate system, of which zeros of y-axis exist on the position of reception effective aperture element array, when performing no steering (θ is zero), as shown in eq. (18a), the wavenumber matching expressed by eqs. (7) and (8) are performed with the twice wavenumber k (i.e., s=2, 2k for reflection waves). This is also for the following SAs. For transmission waves, not 2k but k is used (s=1). This is also for the following SAs.

$\begin{array}{cc}\{\begin{array}{c}{k}_x^{\prime }=k_x\\ k_y^{\prime }=k_y=\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2}\end{array}& \left(18a\right)\end{array}$

[0305] When the steering angle θ is not zero, image signals having the wavenumber vector (sk₀ sin θ,sk₀ cos θ) expressed using the wavenumber vector (0,k₀) with a wavenumber k₀ (=ω₀/c) expressed using the carrier frequency ω₀ of ultrasound signals as the 1st moments (centers) of the multidimensional spectra or the instantaneous frequencies are generated by performing the beamforming, in which the shifting of spectra is performed (FIG. 10). That is, on eqs. (7) and (8), the wavenumber matching expressed by eq. (18b) is performed.

$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+{\mathrm{sk}}_0\sin \theta \end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2}+{\mathrm{sk}}_0\left(-1+\cos \theta \right)\end{array}\end{array}& \left(18b\right)\end{array}$

[0306] The signal processing is performed similarly to the method (1). Particularly, the wavenumber matching is performed, at first, for the spatial (lateral) direction, by multiplying the complex exponential function eq. (19a) expressed using the carrier frequency ω₀ of the ultrasound signals instead of the complex exponential function eq. (9a) prior to performing the Fourier's transform with respect the spatial (lateral) direction and next for the depth direction y, by multiplying the complex exponential function eq. (19c), instead of the complex exponential function eq. (9c), together with the complex exponential function eq. (19b) with removed the performed lateral matching processing eq. (19a) to yield the spatial resolution in the depth direction y instead of the complex exponential function eq. (9b). This processing can be performed when the steering angle is zero degree. This processing is not disclosed in the prior art documents.

exp(ik_x^t)=exp(isk₀ sin θx)  (19a)

exp(I√{square root over ((sk)²−(k_x−k_x^t)²)}y)=exp(i√{square root over ((sk)²−(k_x−sk₀ sin θ)²)}y)   (19b)

exp(ik_y^ty)=exp{isk₀(−1+cos θ)y}  (19c)

[0307] For instance, when using an echo technique (a reflection method), there are cases where the steering angles of transmission and reception beams are different. When the steering angles of the transmission and reception beams are respectively θ_t and θ_x, the wavenumber matching expressed by eq. (18c) with s=2 is performed on eqs. (7) and (8).

$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k_0\left(\sin {\theta }_t+\sin {\theta }_r\right)\end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2}+k_0\left(-2+\cos {\theta }_t+\cos {\theta }_r\right)\end{array}\end{array}& \left(18c\right)\end{array}$

[0308] The signal processing is performed similarly to the cases where the steering angles of transmission and reception beams are same. Particularly, the wavenumber matching is performed, at first, for the spatial (lateral) direction, by multiplying the complex exponential function eq. (19d) expressed using the carrier frequency ω₀ of the ultrasound signals instead of the complex exponential function eq. (19a) prior to performing the Fourier's transform with respect the spatial (lateral) direction and next for the depth direction y, by multiplying the complex exponential function eq. (19f), instead of the complex exponential function eq. (19c), together with the complex exponential function eq. (19e) with removed the performed lateral matching processing eq. (19d) to yield the spatial resolution in the depth direction y instead of the complex exponential function eq. (19b). This processing can be performed when the steering angles θ_t and θ_r are zero degree. This processing is not disclosed in the prior art documents.

exp(ik_x^tx)=exp{ik₀(sin θ_t+sin θ_r)x}  (19d)

exp(i√{square root over ((sk)²−(k_x−k_x^t)²)}y)=exp(i√{square root over ((sk)²−{k_x−k₀(sin θ_t+sin θ_r)}²)}y)  (19e)

exp(ik_y^ty)=exp{ik₀(−2+cos θ_t+cos θ_r)y}  (19f)

[0309] Using the respective eqs. (19a) to (19c) and eqs. (19d) to (19f), the wavenumber matchings expressed by eqs. (18b) and (18c) can be performed on the 2D Fourier's transform R′(k_x,k) with no approximate interpolations similarly to the combinations of eqs. (7) and (8). Alternatively, the beamformings can also be performed with approximate interpolations and with a high speed, in which F(k_x′, k_y′) is 2D inverse-Fourier's transformed. Regarding eqs. (18b) and (18c), also the approximate wavenumber matching about eq (18a), corresponding to the case where steering angles are zero degree, is not disclosed in the prior art documents.

[0310] Also when performing 3D wave digital signal processing using a 2D aperture element array, the 3D Cartesian orthogonal coordinate system (x,y,z) expressed by an axial direction y determined by the direction of a flat reception aperture element array (zeros of y-axis exist on the position of reception effective aperture element array) and lateral directions x and z can be used, for instance. When the steering angle being an angle between the beam direction to be generated and the axial direction (y) is expressed using zero or non-zero elevation and azimuth angles, similarly to when performing the 2D wave digital signal processing explained above, the following wavenumber matching is performed on the 3D Fourier's transform of the received signals with respect to the depth (y) and lateral directions (x and z), where (k_x,k_y,k_z) is the wavenumber domain expressed using the wavenumbers k_x, k_y and k_z of the depth (y) and lateral directions (x and z).

[0311] Image signals having the wavenumber vector (sk₀ sin θ cos ψ, sk₀ cos θ, sk₀ sin θ sin ψ) expressed using the wavenumber vector (0, 0, k₀) with a wavenumber k₀ (=ω₀/c) expressed using the carrier frequency ω₀ of waves as the 1st moments (centers) of the multidimensional spectra or the instantaneous frequencies are generated by performing transmission and reception dynamic focusings, in which the shifting of spectra is performed by multiplying the complex exponential function eq. (C41), being expressed using the parameter s being 2 and 1 respectively for the y coordinates of the transmission aperture elements being zero and non-zero, the wavenumber k₀ and an imaginary unit i, to the Fourier's transforms of the received signals in the axial direction y to perform the wavenumber matchings in the lateral directions x and z at fast; and further by multiplying the complex exponential function eq. (C43) to 2D Fourier's transform (2D FFT) of the signals multiplied with eq. C(41) in order to perform the wavenumber matching in the axial direction together with the complex exponential function eq. (C42) with removed the wavenumber matchings performed in the lateral directions x and z. Thus, by performing the wavenumber matching with no approximate interpolations, image signals can be generated on the Cartesian coordinate system directly.

exp{isk₀ sin θ(cos φx+sin φz)}  (c41)

exp(i√{square root over ((sk)²−(k_x−sk₀ sin θ cos φ)²−(k_z−sk₀ sin θ sin φ)²)}y)  (C42)

exp{isk₀(−1+cos θ)y}  (C43)

That is, the acoustic pressure fields generated by the respective plane wave components at the depth y can also be calculated as image signals by summing, with respect to the plural wavenumber k, the 2D inverse Fourier's transform (IFFT) performed with respect to the lateral directions x and z. The calculations can also be performed for a zero steering angle (i.e., the elevation and azimuth angles are zeros) or either angle is zero at least.

[0312] By the processing, the following wavenumber matching [eq. (C44)] can be performed with respect to the 3D Fourier's transform R′(k_x,k,k_z) similarly to eqs. (7′) and (8′). The above-disclosed processing achieves this wavenumber matching with no approximate interpolations, whereas according to eq. (C44) the wavenumber matching can also be performed with approximate interpolations and with a high speed, in which F(k_x′,k_y′,k_z′) is 3D inverse-Fourier's transformed. The processing is not disclosed in the prior art documents.

$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+{\mathrm{sk}}_0\sin \theta \cos \varphi \end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{k^2-k_x^2-k_z^2}+{\mathrm{sk}}_0(-1+\cos \theta )\end{array}\\ \begin{array}{c}{k}_z^{\prime }=k_z+k_z^t\\ =k_z+{\mathrm{sk}}_0\sin \theta \sin \varphi \end{array}\end{array}& \left(\mathrm{C44}\right)\end{array}$

[0313] For instance, when using an echo technique (a reflection method), there are cases where the steering angles of transmission and reception beams are different. When the steering angles of the transmission and reception beams are respectively (an elevation angle, an azimuth angle)=(θ_t, ψ_t) and (θ_r,Φ_r), the signal processing is performed with s=2 similarly to the above-mentioned cases where the angles of transmission and reception beams are same. Particularly, the wavenumber matching is performed, at first, for the spatial (lateral) directions, by multiplying the complex exponential function eq. (D41) expressed using the carrier frequency ω₀ of the ultrasound signals instead of the complex exponential function eq. (C41) prior to performing the Fourier's transform with respect the spatial (lateral) directions and next for the depth direction y, by multiplying the complex exponential function eq. (D43), instead of the complex exponential function eq. (C43), together with the complex exponential function eq. (D42) with removed the performed lateral matching processing eq. (D41) to yield the spatial resolution in the depth direction y instead of the complex exponential function eq. (C42). This processing can also be performed when the steering angles of transmission and reception beams are zero degree (i.e., θ_t, ψ_t, θ_r and ψ_r are zero degree). This processing is not disclosed in the prior art documents.

$\begin{array}{cc}\exp \left[k_0\left\{\sin {\theta }_t\left(\cos {\varphi }_tx+\sin {\varphi }_tz\right)+\sin {\theta }_r\left(\cos {\varphi }_rx+\sin {\varphi }_rz\right)\right\}\right]& \left(\mathrm{D41}\right)\\ \exp \left(1\sqrt{\begin{array}{c}{\left(\mathrm{sk}\right)}^2-{\left\{k_x-k_0\left(\sin {\theta }_t\cos {\varphi }_t+\sin {\theta }_r\cos {\varphi }_r\right)\right\}}^2-\\ {\left\{k_z-k_0\left(\sin {\theta }_t\sin {\varphi }_t+\sin {\theta }_r\sin {\varphi }_r\right)\right\}}^2\end{array}}y\right)& \left(\mathrm{D42}\right)\\ \exp \left(k_y^ty\right)=\exp \left\{k_0\left(-2+\cos {\theta }_t+\cos {\theta }_r\right)y\right\}& \left(\mathrm{D43}\right)\end{array}$

[0314] For the SA that performs both the transmission and reception beamformings in a software fashion, the exchange of transmission and reception is the same processing

[0315] By the processing, the following wavenumber matching [eq. (D44)] can be performed with respect to the 3D Fourier's transform R′(k_x,k,k_z) similarly to eqs. (7′) and (8′). The above-disclosed processing achieves this wavenumber matching with no approximate interpolations, whereas according to eq. (D44) the wavenumber matching can also be performed with approximate interpolations and with a high speed, in which F(k_x′,k_y′,k_z′) is 3D inverse-Fourier's transformed. The processing is not disclosed in the prior art documents.

$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k_0\left(\sin {\theta }_t\cos {\varphi }_t+\sin {\theta }_r\cos {\varphi }_r\right)\end{array}\\ \begin{array}{c}{k}_y^{\prime }=k_y+k_y^t\\ =\sqrt{k^2-k_x^2-k_z^2}+k_0(-2+\cos {\theta }_t+\cos {\theta }_r)\end{array}\\ \begin{array}{c}{k}_z^{\prime }=k_z+k_z^t\\ =k_z+k_0\left(\sin {\theta }_t\sin {\varphi }_t+\sin {\theta }_r\sin {\varphi }_r\right)\end{array}\end{array}& \left(\mathrm{D44}\right)\end{array}$

[0316] Using the SAs (the method (3), i.e., multistatic SA as well as the method (2), i.e., monostatic SA) with respect to the acquired echo signal data for the SAs, arbitrary beamformings can be performed (actually, the processings disclosed in the method (1) or (4) to (7) can yield image signals from the data). Also in the processings for plane wave transmissions (method (1)), by using coding, the SAs can be performed. That is, the signal data for SAs can be obtained by implementing the decoding on the received signals with respect to transmissions of encoded plane waves.

[0317] As also disclosed in the method (1), the steering can be performed on the dynamic focusing. In the method (1), when the physical steering with a steering angle α (including a case of zero degree) is performed at the transmission of plane wave, and the steering with a steering angle θ (including a case of zero degree) is performed of the method (1) is performed as well, it can be interpreted that the pane wave is steered with a transmission steering (α+θ) [the finally generated steering angle is the mean]. Therefore, in the method (1), a plane wave is steered at the transmission with the steering angle α, θ or α+θ and at the reception dynamic focusing, the steering with a reception steering angle (including a case of zero degree) can be achieved by performing the reception steering of the method (2); then the finally generated steering angle is a mean of all the transmission and the reception steering angles. The steering of plane wave in a software fashion (steering angle θ) is, as mentioned in the method (1), used for reinforcing the physical transmission steering (steering angle α), for purely generating the steering of plane wave in a software fashion, or for performing, in a software fashion, the steering of plane wave at the reception in addition to the reception dynamic focusing (including a case of the steering angle φ is zero degree).

[0318] That is, in a 2D case, eqs. (F41), (F42) and (F43) being respective combinations of eqs. (9a) and (19a), eqs. (9b) and (19b) and eqs. (9c) and (19c) are used to similarly perform the beamforming.

exp(ik_x^tx)=exp{(i(k sin θ+k₀ sin φ)x}  (F41)

exp(i√{square root over (k²−(k_x−k_x^t)²)}y=exp(i√{square root over (k²−(k_x−k sin θ−k₀ sin φ)²)}y)   (F42)

exp(ik_y^tyy)=exp[i{k cos θ+k₀(−1+cos φ))}y]  (F43)

[0319] Also in a 3D case, that is, when the plane wave is physically transmitted with elevational (α) and azimuth (β) steering angles (α, β), or at least either steering angle is zero degree, to perform the steering of the plane wave with a steering angle (θ₁,ψ₁) and the steered dynamic focusing with a steering angle (θ₂,ψ₂) in a software fashion (including a case where at least one steering angle is zero degree), eqs. (G41), (G42) and (G43) being respective combinations of eqs. (C21) and (C41), eqs. (C22) and (C42) and eqs. (C23) and (C43) are used to similarly perform the beamforming. The finally generated steering angle is a mean of all the transmission and the reception steering angles.

$\begin{array}{cc}\exp \left[\left\{k\sin {\theta }_1\left(\cos {\varphi }_1x+\sin {\varphi }_1z\right)\right\}+\left\{k_0\sin {\theta }_2\left(\cos {\varphi }_2x+\sin {\varphi }_2z\right)\right\}\right]& \left(\mathrm{G41}\right)\\ \exp \left(\sqrt{\begin{array}{c}(k^2-{\left(k_x-k\sin {\theta }_1\cos {\varphi }_1-k_0\sin {\theta }_2\cos {\varphi }_2\right)}^2-\\ {\left(k_z-k\sin {\theta }_1\sin {\varphi }_1-k_0\sin {\theta }_2\sin {\varphi }_2\right)}^2\end{array}}y\right)& \left(\mathrm{G42}\right)\\ \exp \left[\left\{k\cos {\theta }_1+k_0\left(-1+\cos {\theta }_2\right)\right\}y\right]& \left(\mathrm{G43}\right)\end{array}$

[0320] As mentioned in the method (1), performing the exchanging of the software transmission and reception has the same processings as those of the original beamforming (equivalent). That is, also in these cases, the software transmission and reception can be considered inversely. Also beamformings of various combinations can be performed in a software fashion with respect to arbitrary physical transmission beamformings (for instance, a steered plane wave, a steered fixed focusing beam, a steered dynamic focusing on the basis of SA, a non-steered wave or beam, other various ones). It is possible to perform, in a software fashion, the steerings of a plane wave or a dynamic focusing at the transmission or reception (including a case where at least one steering angle is zero degree) in addition to the physical steering of a generated arbitrary wave or beam (for instance, the above examples including a case where at least one steering angle is zero degree). Particularly, the software plane wave steering is used for reinforcing the physical transmission steering, for purely performing the steering of the physically transmitted arbitrary waves or beams or for performing, in a software fashion, the reception steering in addition to the reception dynamic focusing (including a case where the steering angle φ is zero degree). These are also for 3D beamforming using a 2D array. Others mentioned in the method (1) hold.

[0321] For the beamformings in the 2D case with eqs. (F41), (F42) and (F43) and in the 3D case with eqs. (G41), (G42) and (G43), the wavenumber matchings can also be performed with approximate interpolations and with high speeds.

[0322] In the 2D case, according to eqs. (7) and (8), the wavenumber matching expressed by eqs. (18b) and (18c) is performed with respect to the 2D Fourier's transform R′ (k_x, k) with approximate interpolations [eq. (F44)] and F(kx′,ky′) is 2D inverse-Fourier's transformed. The approximate processings are not disclosed in the prior art documents.

$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k\sin \theta +k_0\sin \phi \\ k_y^{\prime }=k_y+k_y^t\end{array}\\ =\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2}+k\cos \theta +k_0\left(-1+\cos \phi \right)\end{array}& \left(\mathrm{F44}\right)\end{array}$

[0323] In the 3D case, according to eqs. (7′) and (8′), the wavenumber matching expressed by eqs. (C44) and (D44) is performed with respect to the 3D Fourier's transform R′(k_x,k,k_z) with approximate interpolations [eq. (G44)] and F(k_x′,k_y′,k_z′) is 3D inverse-Fourier's transformed. The approximate processings are not disclosed in the prior art documents.

$\begin{array}{cc}\{\begin{array}{c}{k}_x^{\prime }=k_x+k_x^t\\ =k_x+k\sin {\theta }_1\cos {\varphi }_1+k_0\sin {\theta }_2\cos {\varphi }_2\\ k_y^{\prime }=k_y+k_y^t\\ =\sqrt{k^2-k_x^2-k_z^2}+k\cos {\theta }_1+k_0\left(-1+\cos {\theta }_2\right)\\ k_z^{\prime }=k_z+k_z^t\\ =k_z+k\sin {\theta }_1\sin {\varphi }_1+k_0\sin {\theta }_2\sin {\varphi }_2\end{array}& \left(\mathrm{G44}\right)\end{array}$

[0324] When performing cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) (transmissions or receptions, in a radial (r) direction, of waves widely spread in an angle direction (θ)) using a convex-type transducer or a sector scan, or an IVUS etc. (FIG. 7) or using virtual sources set behind physical apertures with arbitrary aperture geometries (FIGS. 8A(a) to (c)), or acquiring echo data for the SAs on the polar coordinate system, similarly to in the method (1), the processing can also be performed with the polar orthogonal coordinate system (r, θ) instead of the Cartesian orthogonal coordinate system (x,y) (the depth y and lateral x coordinates are replaced by r and θ, respectively) and then, image signals can be directly generated on the Cartesian coordinate system (x,y) or the polar coordinate system (r, θ). When using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries as explained above, the beamformings can also be performed similarly to generate, at an arbitrary distance position, the transmission or reception, or both of plane waves (FIGS. 8B(d) to (f)). Performing such beamformings is equivalent to make a formation of a virtual linear-type aperture array (or a plane wave) at the distance position and then, setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually. The distance position can be set in front of as well as behind the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. The virtual linear-type aperture array can also be used not as the virtual sources but the virtual receivers, or both virtual sources and receivers. These are also when performing other transmission beamformings or performing beamformings on the spherical coordinate system. Alternatively, in the same way, when performing cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) (transmissions or receptions, in a radial (r) direction, of waves widely spread in an angle direction (θ)) using a convex-type transducer or a sector scan, or an IVUS etc. (FIG. 7) and using virtual sources set behind physical apertures with arbitrary aperture geometries (FIGS. 8A(a) to (c)), image signals can be directly generated on the Cartesian coordinate system using the method (5). When using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries as explained above, the beamformings can also be performed similarly to generate, at an arbitrary distance position, the transmission or reception, or both of plane waves (FIGS. 8B (d) to (f)). Performing such beamformings is equivalent to make a formation of a virtual linear-type aperture array (or a plane wave) at the distance position and then, setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually. The distance position can be set in front of as well as behind the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. The virtual linear-type aperture array can also be used not as the virtual sources but the virtual receivers, or both virtual sources and receivers. In these cases, the imagings of echo signals and displacement measurements etc. can be performed on the same Cartesian coordinate system consistently. These are also for the polar coordinate system. In these cases, similarly to the method (1), it is possible to perform the processings on arbitrary orthogonal coordinate systems or via transforming the echo signals or measurements to those on other orthogonal coordinate systems. These are also when using 2D arrays for the 3D beamformings. Transmission focusings may also be performed. In these processings, transmission focusing can also be performed. As mentioned above, the virtual source or the virtual receiver are not always positioned behind the physical aperture and can also be set in front of the aperture. Regardless the geometry of a physical aperture, they can be positioned arbitrarily (patent document 7 or nonpatent document 8). Thus, the present inventions are not limited to these. On the wavenumber matching in these beamformings, approximate solutions can also be calculated with approximate interpolations.

[0325] With respect to the received signals, apodizations for the transmission or reception, or the both can be performed at various timings, because the processings are linear. That is, the apodizations can be performed in a hardware fashion when performing the receivings or in a software fashion after performing the receivings. As mentioned above, the apodizations can also be performed at transmissions physically. When performing the wavenumber matching with approximate interpolations, however with high accuracies, on the basis of eqs. (7) and (7′), the approximations are required to be performed with proper over-samplings of data in return an increased calculation amount. In the case, being different from in the case where image signals of arbitrary positions can be generated when no approximate interpolations are performed, it is cautious that the number of data to be used for the Fourier's transforms increases. These processings can be performed similarly to the method (1), and these are also for other methods (3) to (7).

[0326] FIG. 11 shows an illustration of a multistatic type SA. For the multistatic type SA, an ultrasound is transmitted from one element in an array, and echo is received by the plural elements around the transmission element (generally, including the transmission element). Low resolution image signals are generated every one transmission; and generated plural low resolution image signals are superposed to generate a high resolution image signals. To generate the low resolution image signals, the present invention can also be used.

[0327] As mentioned above, generally and traditionally the low resolution echo signals are generated from the echo signals received every the transmissions are performed by the respective transmission elements; and the generated low resolution eco signals are superposed. In contrast, the present invention generates plural sets, respective of which are comprised of signals received at the same positions with respect to the transmission positions; and respective of which are processed by the digital monostatic SA methods to generate plural low resolution image signals and superpose them. In practice, the linear superposition can be performed in a frequency domain prior to the lateral inverse Fourier's transform, which yields a high speed. Specifically, when performing the superposition in the frequency domain, the lateral positions of plural low resolution image signals are adjusted by performing the lateral shifting processings, i.e., by performing the phase rotations in the lateral direction via multiplying the complex exponential functions to data, and then with no approximate interpolations and with high speeds the image signals are generated. The inverse Fourier's transform is performed using IFFT once. To generate the respective low resolution echo signals to be superposed in a spatial domain, the multiplications of complex exponential functions for rotating the phases in the lateral direction (the lateral shifting processings) can also be performed simultaneously when performing the lateral inverse Fourier's transform. In this case, exclusive IFFT can be performed.

[0328] Important is that when using the program of monostatic type SA, if s=2, the distance of propagation path with respect to the point of interest, to which distance is y (coordinate y), between the transmission and the reception element positions, which are positioned at y=0 and have the distance between the elements Δx in the x-direction, is converted to y′ and further when the steering angle is zero degree, the converted distance y′ is expressed by eq. (20a). Also, if s=1, when the steering angle is zero degree, the converted distance about the point of interest, to which distance is y (coordinate y), is expressed by eq. (20b) with respect to the transmission element positioned at y=Y (non-zero) and the reception element positioned at y=0 with the element distance Δx in the x-direction. The coordinates y of the transmission and reception positions can be considered inversely.

y′=(y+√{square root over (y²+Δx²))}÷2  (20a)

y′=y+√{square root over ((Y−y)²+Δx²)}  (20b)

[0329] When the steering angle is θ (including non-zero degree), the beams are generated by the multistatic SA, to which at least the reception dynamic focusing is implemented (when s=2, the transmission dynamic focusing can also be realized). Waves are transmitted from the respective transmission aperture elements in the transmission effective aperture element array and the waves arriving from the measurement object are received at least by one reception aperture element, in plural reception aperture elements, existing at a different position from that of the transmission element to generate the reception signals (even when one element is used, the instrument of the present invention can also perform the processing). To generate waves that are at least reflected or backscattered waves (s=2), or at least transmission, forward scattered or refracted waves (s=1), the transmission aperture elements are used such that the position has arbitrary x coordinates regardless the x coordinates of reception aperture elements that generate the received signals. The transmission element can also be, positioned at a constant zero y-coordinate, i.e., one of the reception aperture elements in the reception effective aperture element or different element from the reception aperture elements, or positioned at a constant non-zero y-coordinate, i.e., one of the plural transmission aperture elements in the transmission effective aperture element array faced to the reception effective aperture element array (when s=1, the y coordinates of transmission and reception can be considered inversely).

[0330] That is, when performing the steering, the above-mentioned data for the monostatic SA processing, comprised of data generated by the combination of the transmission and the reception elements with same distances, are respectively processed using the steering disclosed in the method (2) and similarly, the processing can be performed. These are also when the transmission and the reception steering angles are different. When the steering angle is non-zero and the program of the monostatic SA processing is used, similarly to the case where steering angles are zero degree, the converted distances expressed by eqs. (20a) and (20b) are respectively used for s=2 and 1 with respect to the distance y (y coordinate) to the point of interest. Thus, similarly to the methods (1) and (2), the processing can be performed using zero or non-zero steering angles on the programs that allow steerings.

[0331] For the transmission, the plane wave transmission of the method (1) can also be performed, and arbitrary transmission beamformings such as a fixed focusing etc. can also be performed etc.

[0332] As other methods, when the y coordinates of the transmission and reception elements are zero, with respect to the same sets of received signals obtained for the same distances Δx in the lateral coordinate for the positions of transmission and reception, using the half distance between the transmission and the reception aperture elements via the point of interest (eq. (20c)) expressed using the steering angle θ, the y coordinate of the point of interest and the distance Δx for s=2, or the distance between the transmission and the reception aperture elements via the point of interest (eq. (20d)) expressed using the steering angle θ, the y coordinate of the point of interest, the y coordinate of the transmission aperture element (y=Y, i.e., non-zero y) and the distance Δx for s=1 (the y coordinates of transmission and reception can also be considered inversely) for the above-disclosed monostatic SA allows generating image signals via spatial corrections of the lateral positions in a frequency domain with respect to the steered image signals and superposition of the corrected image signals, with no approximate interpolations. Although the spatial resolution in the depth direction decreases, a large steering angles can be generated.

y′=(y/cos θ+√{square root over (y²+(y tan θ−Δx)²)})÷2  (20c)

y′=y/cos θ+√{square root over ((y tan θ−Δx)²+(y−Y)²)}  (20d)

[0333] When performing the 3D wave digital signal processing is performed using the 2D aperture element array, for instance, on the Cartesian coordinate system of which y-axis is determined by the direction of a face of flat reception aperture element array and the lateral coordinates x and z are determined such that the axes are orthogonal to the y-axis, similarly to the 2D processing case, the zero or non-zero steering elevational and azimuth angles can be generated regarding the beam direction generated and the axial direction. Waves are transmitted from the respective transmission aperture elements in the transmission effective aperture element array and the waves arriving from the measurement object are received at least by one reception aperture element, in plural reception aperture elements, existing at a different position from that of the transmission element to generate the reception signals. To generate waves that are at least reflected or backscattered waves (s=2), or at least transmission, forward scattered or refracted waves (s=1), the transmission aperture elements are used such that the position has arbitrary x and z coordinates regardless the x and z coordinates of reception aperture elements that generate the received signals. The transmission element can also be, positioned at a constant zero y-coordinate (s=2), i.e., one of the reception aperture elements in the reception effective aperture element or different element from the reception aperture elements, or positioned at a constant non-zero y-coordinate (s=1), i.e., one of the plural transmission aperture elements in the transmission effective aperture element array faced to the reception effective aperture element array (when s=1, the y coordinates of transmission and reception can be considered inversely).

y′=(y+√{square root over (y²+Δx²+Δz²)})÷2  (20e)

y′=y+√{square root over ((Y−y)²+Δx²+Δz²)}  (20f)

[0334] For the transmission, the plane wave transmission of the method (1) can also be performed, and arbitrary transmission beamformings such as a fixed focusing etc. can also be performed etc.

[0335] As other methods, when the y coordinates of the transmission and reception elements are zero, with respect to the same sets of received signals obtained for the same distances Δx and Δz in the lateral coordinates for the positions of transmission and reception, using the half distance between the transmission and the reception aperture elements via the point of interest expressed using the steering elevational and azimuth angles θ and ψ, the y coordinate of the point of interest and the distances Δx and Δz for s=2, or the distance between the transmission and the reception aperture elements via the point of interest expressed using the steering elevational and azimuth angles θ and ψ, the y coordinate of the point of interest, the y coordinate of the transmission aperture element (y=Y, i.e., non-zero y) and the distances Δx and Δz for s=1 (the y coordinates of transmission and reception can also be considered inversely) for the above-disclosed monostatic SA allows generating image signals via spatial corrections of the lateral positions in a frequency domain with respect to the steered image signals and superposition of the corrected image signals, with no approximate interpolations. Although the spatial resolution in the depth direction decreases, a large steering angles can be generated.

[0336] To generate image signals that expresses unknown wave sources or the wave propagations generated by the unknown sources (passive mode), the beamformings can also be performed via setting estimates of y coordinates of the unknown sources at the y coordinates of the transmission aperture elements. It is also effective to perform the observing with changing the setting of y-coordinates of transmission elements by trial and error. For instance, it is better that the image is to be formed, the spatial resolution increases, the signal amplitude increases, the contrast increases etc., and using these as criteria for the judgement, the series of processings can also be performed automatically.

[0337] As mentioned later, as information about the wave source positions or the transmission aperture elements, the positions with respect to the reception aperture elements, the directions of positions or distances to the positions, the direction of aperture or the propagation directions of generated waves can also be given occasionally. The time when waves are generated by arbitrary wave sources can also be given. The wave sources can also be observed using other instruments. Otherwise, the received signals can also convey the information or other waves can be generated, propagating with higher speeds, and can also convey the information etc.

[0338] The beamformings can also be performed by calculating the directions of wave source positions or the wave propagation directions via estimating the 1st moment (center) frequencies of the multidimensional spectra or the instantaneous frequencies with respect to the received signals; and also by regulating the transmission or reception steering angle. Alternatively, with respect to the generated image signals, the beamformings can also be performed by calculating the directions of wave source positions or the wave propagation directions via estimating the 1st moment (center) frequencies of the multidimensional spectra or the instantaneous frequencies; and also by regulating the transmission or reception steering angle. These processings can also be performed using plural reception apertures or plural reception effective apertures, the positions and directions of the wave sources can also be calculated geometrically. These processings are useful and can also be applied to other beamformings.

[0339] As explained in the monostatic SA (method (2)), using the multistatic SA (method (3)) allows performing arbitrary beamformings by using the echo data acquired for the multistatic SA (In fact, the image signals can be generated by implementing the method (1) or (4) to (7) on the data). Although the larger amount of data to be used for the multistatic SA than that for the monostatic SA can be effective, the calculation amount increases. For plane wave processing (method (1)), the SAs can also be performed using the coding. When performing cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) (transmissions or receptions, in a radial (r) direction, of waves widely spread in an angle direction (θ)) using a convex-type transducer or a sector scan, or an IVUS etc. (FIG. 7) or using virtual sources set behind physical apertures with arbitrary aperture geometries (FIGS. 8A(a) to (c)), or acquiring echo data for the SAs on the polar coordinate system, similarly to in the method (1), the processing can also be performed with the polar orthogonal coordinate system (r,θ) instead of the Cartesian orthogonal coordinate system (x,y) (the depth y and lateral x coordinates are replaced by r and θ, respectively) and then, image signals can be directly generated on the Cartesian coordinate system (x,y) or the polar coordinate system (r, θ). These can also be performed when performing other transmission beamformings or performing beamformings on the spherical coordinate system. Alternatively, in the same way, when using a convex-type transducer or a sector scan, or an IVUS etc. and using virtual sources set behind physical apertures with arbitrary aperture geometries, image signals can be directly generated on the Cartesian coordinate system using the method (5). In the case, the imagings of echo signals and displacement measurements etc. can be performed on the same Cartesian coordinate system consistently. In these cases, similarly to the method (1), it is possible to perform the processings on arbitrary orthogonal coordinate systems or via transforming the echo signals or measurements to those on other orthogonal coordinate systems. Otherwise, the beamformings disclosed in the paragraphs 0209 to 0220 etc. in the method (1) and in the paragraphs 0238 etc. in the method (2) can be performed in the same ways and for instance, virtual sources or virtual receivers can be used at arbitrary positions regardless the geometry of physical aperture (patent document 7 and nonpatent document 8). The inventions are not also limited to these (also below).

[0340] Also as disclosed above, although the depth resolution decreases, large steering angles can also be generated using other steering methods. In the cases, different transmission and reception steerings can also be generated. The converted distances expressed using the lateral distances between the transmission and the reception elements, the transmission and reception steering angles and for the transmission cases, the distances between the transmission and the reception elements can be calculated and used.

[0341] Basically, the steerings to be performed using the method (3) are also performed in a software fashion. The apodizations can also be performed at the transmissions or are not performed. The reception apodizations are linear processings and then can be performed at various timings (in a hardware or software fashion). For instance, when performing the software apodizations, the calculation amounts being dependent on the effective aperture width etc. that determines the number of low resolution echo signals to be generated are considered to allow performing the apodizations simply at a proper timing. For instance, the apodizations can be performed with respect to the respective sets for generating the low resolution echo signals, or the generated low resolution signals in a frequency or spatial domain.

[0342] Also for the application of the monostatic SA (method (2)), the wavenumber matching can also be performed with above-disclosed approximate interpolations and with high speeds. For the approximate interpolations, the linear interpolations or using the most neighborhood data themselves approximately can also be performed, or high order approximate interpolations or using the sinc functions can also be performed. To increase the accuracies of the wavenumber matchings to be performed with approximate interpolations, proper over-samplings of data are required in return an increased calculation amount. In the case, being different from in the case where image signals of arbitrary positions can be generated when no approximate interpolations are performed, it is cautious that the number of data to be used for the Fourier's transforms increases.

[0343] Also for the adjusting the lateral positions of the low resolution image signals to be superposed (disclosed in the paragraphs 0241, 0245 and 0248), instead of the high accuracy processing that the complex exponential functions are multiplied in a frequency domain to rotate the phase in the lateral direction, spatial shifting processing can also be performed with approximate interpolations to achieve the higher speed processings. For the approximate interpolations, the linear interpolations or using the most neighborhood data themselves approximately can also be performed, or high order approximate interpolations or suing the sinc functions can also be performed. Also in the cases, to increase the accuracies of approximate interpolations, proper over-samplings of data are required in return an increased calculation amount.

[0344] FIG. 12 shows an illustration of a fixed focusing performed using a linear array-type transducer. The fixed focusing is to make ultrasound waves transmitted from the respective transmission elements to arrive at the focusing position at the same time by setting delays for the transmissions on the respective transmission elements (channels). The measurement object is scanned by receiving waves using the partial or whole physical aperture of the array type transducer as an effective aperture. Off course, the steering can also be performed. The angles of transmission and reception steerings can also be different.

[0345] The fixed focusing can be performed to generate image signals using the method (1), i.e., beamforming for plane wave transmission or the method (3), i.e., the multistatic type SA, or the combinations of the method (1) for the beamforming for plane wave transmission and the method (2) or (3) for the reception dynamic focusing. In the cases, the following three methods can be performed.

(i) Implementing image signal generation processing once on superposing of the respective reception signals obtained at the effective aperture width.
(ii) Superposing of general low resolution image signals generated using reception signals obtained with respect to the respective transmissions.
(iii) Superposing of low resolution image signals generated performing the same processings as those of the multistatic SA, i.e., the respective low resolution image signals are generated with respect to the respective data sets comprised of data with same position relationships between the transmissions and the receptions.

[0346] When performing cylindrical wave transmissions or receptions on the polar coordinate system (r,θ) using a convex-type transducer or a sector scan, or an IVUS etc. or using virtual sources set behind physical apertures with arbitrary aperture geometries, the processing can also be performed with the polar orthogonal coordinate system (r,θ) instead of the Cartesian orthogonal coordinate system (x,y) (the depth y and lateral x coordinates are replaced by r and θ, respectively) and then, image signals can be directly generated on the polar coordinate system (r,θ). As mentioned above, approximate interpolations are required after generating the image signals. These are also when performing the transmission and the reception beamformings on the spherical coordinate system. In the prior art document 6, a beamforming method for the transmission focusing with approximate processings is disclosed and similarly, the results are obtained on the polar coordinate system (r,θ). The inventor of the present invention also invented the beamforming methods (5), (5-1), (5-1′) and (5-2) for generating image signals directly on the Cartesian coordinate system as the results of beamformings with respect to transmissions and receptions performed on the polar coordinate system, the spherical coordinate system or arbitrary orthogonal curvilinear coordinate systems. In the case, the imagings of transmission waves, reflected waves, scattered waves or attenuated waves etc. and displacement measurements etc. can be performed on the same Cartesian coordinate system consistently. In these cases, similarly to the method (1), it is possible to perform the processings on arbitrary orthogonal coordinate systems or via transforming the echo signals or measurements to those on other orthogonal coordinate systems. Otherwise, the beamformings disclosed in the paragraphs 0209 to 0220 etc. in the method (1) and in the paragraphs 0238 etc. in the method (2) can be performed in the same ways and for instance, virtual sources or virtual receivers can be used at arbitrary positions regardless the geometry of physical aperture (patent document 7 and nonpatent document 8). The inventions are not also limited to these (also below). Also, as mentioned above, the steering can also be performed. The cases where the steering angles of physical transmission beamforming and software reception beamforming are different can also be realized. In addition, software transmission steering can also be implemented. In the cases, the steering angle can also be different from other steering angles. For the reception, physical beamformings can also be performed. It is possible to interpret the transmission and reception inversely. The apodizations can also be performed at the transmissions and with respect to the received signals, the reception apodization processings can also be performed (in a hardware fashion at the receptions or in a software fashion after the receptions). The software apodizations can be performed according to the method (1) or (3). Similarly, the apodizations can also be performed when the combination of the method (1) for the plane wave transmission beamforming and the method (2) or (3) for the reception dynamic focusing.

[0347] Theoretically and in practice, the method (4) using the method (1) for processing the plane wave allows arbitrary physical transmissions or the reception beamformings. By performing the processings as mentioned above, various combinations of beamformings can be performed (For instance, for the plane wave transmission and the reception dynamic focusing, the proceedings such as focusings, steerings, apodizations etc. that can be performed physically, at transmissions and receptions, by using calculators or exclusive devices etc. others from those performed in software beamformings using calculators or exclusive devices etc., can be respectively performed, or both the physical and software processings can be performed. Also the transmissions and receptions can be considered inversely as mentioned above). For instance, as mentioned in the paragraphs 0107, 0110, 0363, 0365, 0366 etc., regardless the physical focuses (subaperture widths, distances or depths, positions etc.) being same or not, or the physical transmission steering angles being same or not, the above-mentioned processings mentioned in the method (4) is effective for simultaneous transmissions of plural beams including physically steered or non-steered ones, or occurrences of interferences of beams or not, such transmissions, however, at different timings, but, on the same phase of the object, or the mixed transmissions. Particularly, the method (i) that performs the processing once for generating image signals with respect to the superposition of the respective reception signals obtained at effective aperture widths yields a high frame rate. Using the method (4) does not always require beamformings to be performed at positions where the interferences of beams do not occur (mentioned in the paragraphs 0030, 0362, etc.). Even if over-lapped subapertures are simultaneously used etc. or the interferences occur, the same processings realize the high frame rate. At the time, if respective the software transmission steering angles and the software reception steering angles to be implemented on the plural focused beams are same, the above-mentioned processings can be performed. When plural transmissions such as plural positioned focusings or transmission dynamic focusing are performed on the same phase of the object, the superposition of received signals can also be processed similarly. Regarding the received signals obtained at the same phase of the object, if the received signals are superposed such that the positions (time) of signals are adjusted on the basis of the transmission element position or the timing, all the cases can be processed by the method.

[0348] When either the software transmission steering angles or the software reception steering angles to be implemented on the plural focused beams include at least a different angle, the received signals are separated into those with same steering angles, and the respective separated, received signals with the same steering angles are processed, after which the processed results are superposed in a frequency domain to generate the final result. With respect to one physical transmission beam (steered or non-steered one), plural steered reception beams (a zero steering angle can be included) can also be generated and similarly processed. Also when performing plural different physical steerings, the received signals are separated into those with same steering angles, and the respective separated, received signals are processed to generate the results, or the received signals are also processed without performing the separation. When performing the separations, the superpositions can also be performed in a spatial or frequency domain.

[0349] When physically performing the transmitting in plural directions, specific transmission and reception steerings can also be implemented on the respective physical transmission steerings. In the cases, the signals generated by the respective transmitted beams can be separated in a frequency domain or the independent component analysis (many literatures exist such as a rather classical one, Te-Won Lee, Independent Component Analysis: Theory and Applications, Springer, 1998 as well as others) and the processing can be performed. Analogue devices can also be used. For instance, the same steering angles can be set on the software transmission or reception steering angle as that of the physical steering angle used. Other signal separation methods are also mentioned (for instance, the paragraph 0368).

[0350] Here, mentioned is the using of these methods on various fixed focusing processings. These methods are not limited to these and can also be used for other transmission beamformings. Similarly, the beamformings with new properties that cannot be achieved by a single beamforming by performing plural transmissions or receptions of waves or ultrasounds with different parameters such as a focusing (multi-focusings that generate plural different focusing positions with respect to the effective aperture) or a non-focusing, a steering (plural steerings with different steering angles) or a non-steering, an apodization (changeable with positions) or a non-apodization, an F-number, a transmission ultrasound frequency or a transmission bandwidth, a reception frequency or a reception bandwidth, a pulse shape, a beam shape etc. For instance, it is known that the superposing yields plural focusings or wide bandwidths in the depth and lateral directions (high spatial resolutions). These processings can be speeded up. To obtain the harmonic waves, the so-called pulse inversion method (transmissions of pulses with inverse polarities as a ultrasound parameters) etc. can be performed by superposing the received signals and similarly, the high speed processing can be performed. Off course, after performing the beamformings, the received signals can also be superposed. More than two plural beams can also be superposed.

[0351] On the basis of the considerations of the transmissions and receptions in an inverse fashion, the above-mentioned processings can also be performed simultaneously on the reception beamforming(s). Otherwise, the above-mentioned processings can also be performed on both transmission(s) and reception(s).

[0352] When the separated beamformings are performed, parallel processings can also be performed. The separations can be performed the position in an ROI as well as the above-mentioned various parameters of waves or ultrasounds such as a steering angle etc. One reception signal can also be used for various purposes such as imaging, measurement, treatment etc. via generating, by performing beamformings, informative waves (including much information) such as transmission signals, reflection signals, scattering signals, attenuation signals etc. with high accuracies and high spatial resolutions and performing post-processings such as filtering to yield signals adapted for the respective purposes. According to the respective purposes, proper beamformings can also be performed and the processings can also be performed in a parallel fashion.

[0353] The present invention allows performing beamformings for such as arbitrary beam transmissions such as fixed, focused beams etc., arbitrary wave transmissions (including non-beamformed waves), superposition of transmissions of plural beams or waves and simultaneous transmissions of plural beams or waves. That is, whenever any single or plural transmissions are performed, “the reception beamformings” (dynamic focusing etc.) can be performed at once. Plural beamformings can also be performed by using the multi-directional synthetic aperture (SA) method (past invention of the inventor of the present invention) and in the cases, similarly the processings can be performed with high speeds. The present inventions are not limited to these.

[0354] One of the features of present invention is to perform the wavenumber matchings with no approximate interpolations. However, also in the method (4) using the above-mentioned methods (1) to (3), similarly to the methods (1) to (3), approximate interpolations can be performed on the wavenumber matchings (approximate wavenumber matchings mentioned for the respective beamformings) and the beamformings can also be completed with high speeds. To increase the accuracies of the wavenumber matchings to be performed with approximate interpolations, proper over-samplings of data are required in return an increased calculation amount. In the case, being different from in the case where image signals of arbitrary positions can be generated when no approximate interpolations are performed, it is cautious that the number of data to be used for the Fourier's transforms increases.

[0355] Method (5) is used to generate image signals on the Cartesian coordinate system when performing, by using the convex-type array or sector scanning, IVUS etc., the transmissions and receptions of ultrasound cylindrical waves (or the partial waves) on the 2D polar coordinate system (r, θ) (FIG. 7). The methods (1) to (4) and (6) can be performed.

[0356] Below explained are the expression of Fourier's transform using the polar coordinate system. The 2D Fourier's transform is expressed by eq. (22).

F(k_x,k_y)=∫∫f(r,θ)e^{−i(kxx+kyy)}dxdy  (22)

The reception signals are expressed as f(r,θ) on the polar coordinate system and then, eq. (23) holds.

x=r sin θ, y=r cos θ  (23)

[0357] Then, eq. (24) can be obtained via the Jacobi operation. Thus, the wave expressed on the polar coordinate system can be decomposed into plane wave components (k_x,k_y) on the Cartesian coordinate system. Waves expressed on arbitrary orthogonal curvilinear coordinate systems can also be decomposed into the plane wave components (k_x,k_y) similarly.

F(k_x,k_y)=∫∫f(r,θ)|r|e^{−i(kxr sin θ+kyr cos θ)}drdθ  (24)

[0358] FIG. 13 shows a flowchart about the digital signal processing for a cylindrical wave transmission. According to eq. (24), the Fourier's transform along the aperture in the angle direction θ is expressed as eq. (25).

U(k_x,k_y)=∫u(k,θ)r₀e^{−i(kxr0sin θ+kyr0cos θ)}dθ  (25)

or

U(k_x,k_y)=∫u(k,θ)r₀e^{−i(kxx0+kyy0)}dθ  (25′)

Here, r₀ is a curvature radius of the convex-type transducer; x₀ and y₀ are x and y coordinates expressing the array element positions (those of convex-type array transducer). At the step S21, the received signals are Fourier's transformed (FFT) regarding the time t and at the step S22, the received signals are Fourier's transformed (FFT) regarding the angle θ; achieving the decomposition of the signals received on the polar coordinate system into the plane wave components (k_x,k_y) on the Cartesian coordinate system.

[0359] Thus, for instance, the wavenumber matching expressed by eq. (26) is implemented on the spectra at the step S23 and by subsequently performing the inverse Fourier's transforms on the space (x,y), the image signals are generated.

U′(k_x,k_y)=U(k_x,k_y)e^{−ik(r−r0)}  (26a)

[0360] Moreover, at the step S24, the following complex exponential function is multiplied to the 2D spectra to calculate the angular spectra at the respective depths.

exp(i√{square root over (k²−k_x²)}y)  (26b)

[0361] Otherwise, the calculations of the steps 23 and 24 can be performed inversely.

[0362] Otherwise, without using eqs. (26a) and (26b), according to the method (5), the following complex exponential function is straightforwardly multiplied to yield the angular spectra at the respective depths y as well as to perform the wavenumber matching.

exp{i(√{square root over (k²−k_x²)}+k)y}  (26c)

[0363] Moreover, for instance, at the step S25, summing of the angular spectra is performed with respect to the frequency (k) components and at the step S26, the inverse Fourier's transform (IFFT) is performed in the lateral direction k_x and at the step S27, the image signals are generated. Purely, the 2D inverse Fourier's transform can also be implemented.

[0364] When performing the steering, according to eqs. (9a) to (9c) of the method (1), with performing the wavenumber matchings in the x and y directions, the spatial resolutions can be obtained. As mentioned later, when the calculations are performed on the polar coordinate system (r,θ), the steering angle is set on the polar coordinate system (an angle between the steered direction and the radius direction) and similarly, steering can also be performed. Similarly to the method (1) etc. and other methods, physical steering can also be performed, software steerings of transmission, reception or both the transmission and reception can also be performed, the combinations of the physical and software steerings can also be performed.

[0365] This method is used for performing beamformings to directly generate image signals on the Cartesian coordinate system (x,y) from the signals acquired on the polar coordinate system (r,θ) via no approximate wavenumber matchings and the coordinate conversion and with high speeds and with high accuracies. Similarly to the plane wave transmission performed using a linear array-type transducer, steering can also be performed with respect to the cylindrical wave on the polar coordinate system. Similarly, the cases where steering angles of the transmission and reception beamformings are different etc. can also be processed. The steerings can also be performed in a software fashion. Apodizations can also be performed. When using the cylindrical wave, at plural positions on the z axis orthogonal to the 2D polar coordinate system (i.e., the z-axis of the cylindrical coordinate system (r,θ, z)), the above-mentioned transmissions can be performed simultaneously and reception can be performed, or the above-mentioned transmissions can be performed at different times, however, at the same phase of the object, and reception performed can be superposed. For these, the above-mentioned processings can also be performed. In the z-axis, focusing can also be performed using an analogue device (lens), or arbitrary processings can also be performed using the digital signal processing of the present invention. When the wave propagation directions point to an origin of the polar coordinate system, the beamformings can be performed similarly (For instance, useful for a HIFU treatment, various type imagings using circular array-type transducers that encircles the objects or a CT etc.). Off course, in the cases, only the reception beamformings can also be performed and similarly can be processed. With respect to the received signals expressed on the polar coordinate system (r,θ), the processings mentioned in the method (1), however, with exchanging the Cartesian coordinate system by the polar coordinate system (r,θ), can also be performed to generate image signals on the polar coordinate system (r,θ) as mentioned above. When generating the image signals on the Cartesian coordinate system from the results, approximate interpolations are performed as post-processings. In these, steering can also be performed similarly. The methods (2) to (4) and (6) can also be performed similarly.

[0366] Also when the received signals are expressed as digital signals on the Cartesian coordinate system (x,y), inversely to eq. (22), f(x,y) is Fourier's transformed with respect to the radius r and the angle θ, and image signals can also be generated on the polar coordinate system (r,θ) after all. Otherwise, using the respective methods also allows generating image signals on the Cartesian coordinate system (x,y). Steering and apodization can also be performed similarly.

[0367] As shown in FIGS. 8B(d) to (f), when using the physical aperture element arrays expressed by the polar system or the physical apertures with arbitrary aperture geometries as explained above, the beamformings can also be performed similarly to generate, at an arbitrary distance position, the transmission or reception, or both of plane waves. The image signals can be generated on the Cartesian coordinate system, the polar coordinate system or orthogonal curvilinear coordinate system set according to the physical aperture geometry. Performing such beamformings are equivalent to make a formation of a virtual linear-type aperture array (or a plane wave) at the distance position and then, setting the distance position zero corresponds to the case where a linear-type aperture array is used at the position virtually. The distance position can be set in the front of as well as behind the physical aperture and then, the virtual linear-type aperture array (or a plane wave) can be generated at the distance positions. Virtually, the plane wave can also be steered or the linear-type aperture array can also be slanted (Virtually, the mechanical steering can also be performed). Off course, if required, the physical aperture can also be mechanically steered. The transmissions or the receptions of such plane waves can be performed on the basis of the transmissions and the receptions of the cylindrical waves, respectively, and occasionally, other beamformings can also be performed.

Method (5-1′): Image Signal Generation Using Virtual Source and Aperture Array with Other Arbitrary Geometries

[0368] In cases where waves are transmitted from arbitrary aperture geometries such as a linear-type array transducer as well as the circular aperture arrays and specifically, generations of partial cylindrical waves using virtual sources set behind the physical apertures are explained (FIGS. 8A(a) to (c)).

(i) When using the reception signals acquired for monostatic SAs, the reception signals stored in memories etc., i.e., the reception signals received by the respective transmission elements themselves, are Fourier's transformed and if necessary, the calculated spectra are multiplied with complex exponential functions to express the responses with respect to the waves transmitted from the virtual source as the digital signals on the polar coordinate system (r,θ), and the method (5) or (5-1) can be used to generate image signals on the Cartesian coordinate system (x,y) directly. Alternatively, after the received signals are expressed as the digital signals on the polar coordinate system (r,θ) in the same way, the processings mentioned in the method (1), however, with exchanging the Cartesian coordinate system by the polar coordinate system (r,θ), can also be performed to generate image signals on the polar coordinate system (r,θ). Off course, the monostatic processings in the method (2) can be also performed on the polar coordinate system (r,θ). (ii) When using the reception signals acquired for multistatic SAs, the reception signals stored in memories etc., i.e., the reception signals received at the surrounding reception elements of the respective transmission elements, are Fourier's transformed and if necessary, the calculated spectra are multiplied with complex exponential functions to express the responses with respect to the waves transmitted from the virtual source as the digital signals on the polar coordinate system (r,θ), and the method (3) can be used to perform the multistatic SA. Alternatively, the method (5) can be used, or after superposing the digital reception signals at the respective reception elements, the method (5-1) can be used to generate image signals on the Cartesian coordinate system (x,y) directly. Otherwise, after superposing the digital reception signals at the respective reception elements in the same way, the processings mentioned in the method (1), however, with exchanging the Cartesian coordinate system by the polar coordinate system (r,θ), can also be performed to generate image signals on the polar coordinate system (r,θ). Off course, without performing the superposition, the multistatic processings in the method (3) can also performed on the polar coordinate system (r,θ).
(iii) In these processings, to omit the processings for rewriting the reception signals, received at the physical aperture array, by the digital signals on the polar coordinate system (r,θ), delay patterns for the elements with respect to the transmissions or the receptions are used to perform the transmissions and the receptions such that the reception samplings of the received signals are performed on the polar coordinate system originally. And, using the method (2) or (3), which is on the basis of the method (5) or (5-1), can generate image signals directly on the Cartesian coordinate system (x,y). Alternatively, after obtaining the digital signals on the polar coordinate system (r,θ) in the same way, the processings mentioned in the methods (1) to (3), however, with exchanging the Cartesian coordinate system by the polar coordinate system (r,θ), can also be performed to generate image signals on the polar coordinate system (r,θ).
(iv) Also, in the same way, on the above-mentioned (i) to (iii) in the cases where the partial cylindrical wave is generated using the virtual source behind the arbitrary aperture geometry (FIGS. 8A(a) to (c)), the reception signals stored in memories etc., i.e., the reception signals received by the respective elements, are Fourier's transformed; and the calculated spectra are multiplied with complex exponential functions (times required) or approximate interpolations are performed to rewrite the reception signals by the digital signals on the Cartesian coordinate system (x,y); and f(x,y) is Fourier's transformed in the directions of a radius r and an angle θ (inversely to eq. (22) in the method (5-1)) to generate image signals on the polar coordinate system (r,θ) after all, or using the respective methods can also generate image signals on the Cartesian coordinate system (x,y). When using orthogonal curvilinear coordinate systems (curvilinear coordinate systems) set according to the aperture geometry, image signals can be generated similarly.

[0369] Otherwise, on (i) to (iv), various beamformings etc. mentioned in the method (5-1) can be performed.

[0370] As mentioned in the method (1) etc., when a cylindrical wave is transmitted (transmission delays can be used) using the virtual source set behind arbitrary aperture (one of apertures of a linear-type array transducer or other types, or quasi-array apertures generated by mechanical scanning etc.) (FIGS. 8A(a) to (c)), the transmission is encoded by implementing the coding on the signals of the respective transmission elements (channels) similarly to the cases of a plane wave transmission; and the received signals are decoded for generating the reception signals for SA processings. Then, by using the above-mentioned processings, image signals are generated directly on the Cartesian coordinate system or arbitrary orthogonal curvilinear coordinate systems such as the polar coordinate system etc. Also, not virtual sources but virtual receivers can also be set and the virtual receivers can also work as the virtual sources.

[0371] Also, as mentioned in the method (1) etc., when a cylindrical wave is transmitted (transmission delays can be used) using the virtual source set behind arbitrary aperture (one of apertures of a linear-type array transducer or other types, or quasi-array apertures generated by mechanical scanning etc.) (FIGS. 8A (a) to (c)), using the above-mentioned methods allows the following processings. (A) With respect to the reception signals expressed on the Cartesian coordinate system (x,y), obtained using the linear-type array transducer or the mechanical scanning, the method (1) itself is used to generate image signals on the Cartesian coordinate system.

(B) With respect to the reception signals received at the reception positions by using the linear-type array transducer or the mechanical scanning, the spectra calculated by (fast) Fourier's transform in the y direction are multiplied with complex exponential functions to perform the spatial shiftings of the signals in the y direction such that on the polar coordinate system (r,θ) having the origin at the position of virtual source, the positions of signals are corrected to the r positions under θ determined by the reception positions; and the method (5) or (5-1) is implemented to the data to generate image signals on the Cartesian coordinate system (x,y) or the polar coordinate system (r,θ). Although not the spatial shiftings using the complex exponential functions but approximate spatial shiftings by zero padding in the signal values in the r coordinates can also be performed, to increase the accuracies of the approximations, proper over-samplings of the received signals are required, i.e., AD convertors with high sampling rates or many memories are required. It is cautious that the number of data to be used prior to the Fourier's transforms increases.
(C) With respect to the reception signals received by arbitrary aperture geometries except for a linear-type array transducer and quasi-linear type array apertures generated by mechanical scanning etc., the method (5) or (5-1) is implemented and in the same way, image signals are generated on the Cartesian coordinate system (x,y), the polar coordinate system (r,θ), the orthogonal curvilinear coordinate system (curvilinear coordinate system) set according to the aperture geometry.
(D) Not virtual sources but virtual receivers can also be used, or the virtual receivers can also work as the virtual sources.

[0372] As the results of these methods (5-1′), for instance, using other type transducers or other mechanical scanning such as a convex-type or sector-type transducer as shown in FIG. 7 (figures of the corresponding mechanical scanning are omitted) can also generate image signals on the Cartesian coordinate system (x,y), the polar coordinate system (r,θ), the orthogonal curvilinear coordinate system (curvilinear coordinate system) set according to the aperture geometry.

[0373] Otherwise, when the virtual linear-type array transducer is realized using the physically other type array transducers inversely (for instance, a physical convex-type array transducer is used, as shown in FIGS. 8B(d) to (f), when the virtual source or the virtual receiver is set at the position of physical aperture, or behind or in front of the physical aperture), image signals can also be generated in the same way on the Cartesian coordinate system (x,y), the polar coordinate system (r,θ), the orthogonal curvilinear coordinate system (curvilinear coordinate system) set according to the aperture geometry.

[0374] Also, in special cases, for instance, when using the linear-type array transducer physically, applications of the generations of cylindrical waves using virtual sources or virtual receivers set behind the physical aperture allows the generations of image signals in the cases where at arbitrary distance positions, a plane wave widely spread in a lateral direction or a virtual linear-type array transducer is generated (FIG. 8B(G)).

[0375] In these cases, the transmissions to be generated or wave receptions can also be steered, or the apertures can also be slanted virtually (mechanical scanning is virtually performed). Off course, if required, physical apertures can also be mechanically scanned.

[0376] FIG. 14 shows an illustration of a fixed focusing performed using a convex-type transducer. Also when using a convex-type transducer, the fixed focusing can be performed. For instance, FIGS. 14(a) and (b) respectively shows cases where the fixed focus positions are equal from the respective effective aperture and arbitrarily set. Similarly to when using a linear-type array transducer (method (4)), image signals can be generated using the same calculations as those performed when the cylindrical wave is transmitted. That is, on the basis of the processings of the method (1) or (3), the following three methods can be performed.

(i) Implementing image signal generation processing once on superposing of the respective reception signals obtained at the effective aperture width.
(ii) Superposing of general low resolution image signals generated using reception signals obtained with respect to the respective transmissions.
(iii) Superposing of low resolution image signals generated performing the same processings as those of the multistatic SA, i.e., the respective low resolution image signals are generated with respect to the respective data sets comprised of data with same position relationships between the transmissions and the receptions.

[0377] By performing the above-mentioned processings, image signals can be generated directly on the Cartesian coordinate system. And, it is also possible to generate image signals on the polar coordinate system by implementing the method (4) with the axes of the polar coordinate system. Similarly, steering and apodization can also be performed. Regarding the direction of z-axis, similar processings to those of the method (5-1) can be performed.

[0378] Also when the received signals are expressed as digital signals on the Cartesian coordinate system (x,y), by implementing Fourier's transforms on f(x,y) regarding the radius r and the angle θ, image signals can be generated on the polar coordinate system (r,θ) after all or image signals can also be generated on the Cartesian coordinate system (x,y) using the respective methods. Steering, apodization and processing in the z-axis can also be performed similarly.

[0379] When performing the steering, according to the method (4), the spatial resolution can be obtained together with performing the wavenumber matchings in the x and y directions. As mentioned later, when performing the calculations on the polar coordinate system (r,θ), similarly the steering can also be performed by setting the steering angle (an angle between the steered direction and the radius direction) on the polar coordinate system similarly. Similarly to the method (1) etc. and other methods, physical steering can also be performed, software steerings of transmission, reception or both the transmission and reception can also be performed, the combinations of the physical and software steerings can also be performed.

[0380] Also, when using virtual sources or virtual receivers, by setting virtual apertures in front of or behind the physical apertures etc. mentioned in the method (5-1′), the above-mentioned, transmission fixed focusing can be performed. For instance, a linear-type array transducer can be realized virtually. Otherwise, transducers with arbitrary aperture geometries can also be realized. Image signals are generated on the Cartesian coordinate system, the polar coordinate system or the orthogonal curvilinear coordinate system. Similarly to the method (1) etc. and other methods, physical steering can also be performed, software steerings of transmission, reception or both the transmission and reception can also be performed, the combinations of the physical and software steerings can also be performed. In these cases, the transmissions to be generated or wave receptions can also be steered, or the apertures can also be slanted virtually (mechanical scanning is virtually performed). Off course, if required, physical apertures can also be mechanically scanned.

[0381] As mentioned above, the beamformings of the methods (1) to (4) can be performed, however, not limited to these. The adaptions of these approaches to arbitrary beamformings yield the same effects. Particularly, when using the method (4), the reception beamforming can be performed with respect to any transmission beams or waves in addition to the transmission fixed focusing. Off course, similarly the beamformings can also be performed on the simultaneous reception signals received with respect to the simultaneous transmissions of plural different beams or waves, or the superposition of reception signals with respect to the respective transmissions.

[0382] When using the wave aperture element array with a spherical kernel geometry, 3D digital wave signal processing can be performed. For instance, when using the type reception aperture element array, receptions of waves are performed on the spherical coordinate system (r,θ,ψ) and then, the reception signals of received waves are expressed by f(r,θ,ψ). In this case, similarly to using the 2D polar coordinate system (r,θ), various beamformings can be implemented using the Jacobi operation.

[0383] Concretely, to decompose the received waves into plane waves on the Cartesian coordinate system (x,y,z), 3D

[0384] Fourier's transform is implemented on the reception signal f (r,θ,ψ), expressed by eq. (27) expressed in the wavelength or frequency domain (k_x,k_y,k_z) with respect to the Cartesian coordinate system (x,y,z). Moreover, the calculation of eq. (28) using the Jacobi operation using x=r sin θ cos ψ, y=r cos θ and z=r sin θ sin ψ on the eq. (27) can generate image signals directly on the Cartesian coordinate system with no approximate interpolations. Off course, the beamformings of the methods (1) to (4) and (6) can be performed, however, not limited to these. The adaptions of these approaches to arbitrary beamformings yield the same effects. Particularly, when using the method (4), similarly to in the 2D case, the reception beamforming can be performed with respect to any transmission beams or waves in addition to the transmission fixed focusing. Off course, similarly the beamformings can also be performed on the simultaneous reception signals received with respect to the simultaneous transmissions of plural different beams or waves, or the superposition of reception signals with respect to the respective transmissions. Also, when using the virtual sources or virtual receivers or performing the steering etc., the all can be performed similarly to in the 2D case and image signals can be generated on the Cartesian coordinate system, the polar coordinate system or the orthogonal curvilinear coordinate system set according to the physical aperture geometry.

$\begin{array}{cc}F\left(k_x,k_y,k_z\right)=\int \int f\left(r,\theta ,\Psi \right)\exp \left\{-\left(k_xx+k_yy+k_zz\right)\right\}xyz& \left(27\right)\\ F\left(k_x,k_y,k_z\right)=\int \int f\left(r,\theta ,\Psi \right)r\exp \left\{-\left(k_x\sin \theta \cos \Psi +k_y\cos \theta +k_z\sin \mathrm{\theta sin}\Psi \right)r^2\sin \theta \right\}r\theta \Psi & \left(28\right)\end{array}$

Method (5″): Image Signal Generation on Arbitrary Orthogonal Curvilinear Coordinate System when Transmission or Reception is Performed on Cartesian Coordinate System

[0385] Inversely to the above-mentioned series of methods, however, with the similar calculations, image signals can be generated directly on the 2D polar coordinate system or the spherical coordinate system with no approximate interpolations from reception signals obtained by performing transmissions and receptions on the Cartesian coordinate system. For instance, when the reception signals are expressed by f(x,y,z), by implementing Fourier's transforms on f(x,y,z) regarding the directions of r, θ and ψ via the Jacobi operation, the reception signals f(x,y,z) are decomposed into the circular waves or spherical waves corresponding to plane waves decomposed into on the Cartesian coordinate system. These methods can also be used for changing FOV (for instance, there is a case where a larger FOV can be obtained). Using the Jacobi operation, image signals can also be obtained on arbitrary orthogonal coordinate systems similarly and whenever transmissions and receptions are performed on arbitrary coordinate systems, image signals can also be generated on arbitrary orthogonal coordinate systems. Similarly to other methods mentioned in the method (5), any transmission beams or waves can also be processed; steering can also be implemented similarly; the virtual sources or the virtual receivers can also be used.

[0386] One of the features of method (5) is to perform the beamformings on arbitrary coordinate systems with no approximate interpolations on the wavenumber matchings. However, when using the method (5) for the methods (1) to (4), the method (5), the method (6) and the method (7) to perform the beamformings with high speeds on arbitrary coordinate systems, approximate interpolations can also be performed on the wavenumber matchings (the respectively mentioned approximate wavenumber matchings). To increase the accuracies of the wavenumber matchings to be performed with approximate interpolations, proper over-samplings of data are required in return an increased calculation amount. In the case, being different from in the case where image signals of arbitrary positions can be generated when no approximate interpolations are performed, it is cautious that the number of data to be used for the Fourier's transforms increases.

[0387] Using the instrument of present invention allows performing for the migration methods no approximate interpolations for the wavenumber matchings. The expression of the migration (below mentioned eq. (M6′)) is well known and the derivation is also well known and then, the derivation is omitted here.

[0388] In the nonpatent document 12, the disclosed method is that the difference in a propagation time from an arbitrary transmission aperture element to the reception aperture element (i.e., the transmission aperture element itself) via an arbitrary same position of interest (i.e., the object position) with respect to the plane wave transmission and/or reception with the steering or no steering (i.e., corresponding to the method (1)) from that on the general migration using one element reception by the one element transmission (i.e., corresponding to the non-steering processing using the method (2) on the transmission and reception data for monostatic SA) is used for performing the calculation of the same type expression of the migration (eq. (M6)), of which the propagation speed and the coordinate of the position of interest (the object position) are modified (i.e., below mentioned eq. (M1)).

[0389] However, regarding the processings of other methods (2) to (5), nothing is disclosed in the nonpatent document 12 (Specifically for the method (2), steering processing is not disclosed). Moreover, for calculating eq. (M6′), approximate interpolations are performed on the wavenumber matching traditionally (eqs. (M4) and (M4′)). In contrast, the instrument of present invention allows performing the wavenumber matching with no approximate interpolations (eqs. (M7) and (M7′)).

[0390] A 2D coordinate system is set with the lateral (x) and depth (y) directions (axes), and the temporal axis is set as t. Concretely, the propagation time required for the round trip between an arbitrary aperture element (x,0) and an arbitrary position of interest (x_s,y_s) is expressed as eq. (M0).

$\begin{array}{cc}\tau \left(x\right)=\frac{2}{c}\sqrt{{\left(x_s-x\right)}^2+y_s^2}& \left(M0\right)\end{array}$

[0391] Alternatively, in the case of a plane wave transmission with a steering angle θ (it can be 0 degree), the corresponding propagation time is expressed as eq. (M0′).

$\begin{array}{cc}\tau \left(x\right)=\frac{1}{\alpha c}\sqrt{{\left(x_s+\gamma y_s-x\right)}^2+{\left(\beta y_s\right)}^2},\mathrm{where}\alpha =\frac{1}{\sqrt{1+\cos \theta +{\sin }^2\theta }},\beta =\frac{{\left(1+\cos \theta \right)}^{\frac{3}{2}}}{1+\cos \theta +{\sin }^2\theta },\gamma =\frac{\sin \theta }{2-\cos \theta }.& \left(M0^{\prime }\right)\end{array}$

[0392] Thus, when performing the beamforming for the steered plane wave transmission of the method (1) by using the migration method, the general migration expressions (eqs. (M4) and (M5)) are calculated by modifying the propagation speed c and the coordinate system (x_s,y_s) expressing the object position by eq. (M1).

ĉ=αc

({circumflex over (x)}_s;ŷ_s)=(x_s+γy_s,βy_s)  (M1)

[0393] Summarizing, all the methods (1) to (5) except for the method (2) performing the non-steering monostatic SA using the transmission and reception SA data (i.e., a general migration method) can also be performed using migration processing similarly. For instance, the migration calculation procedure is explained mainly for the steered plane wave transmission (the steering angle can be 0 degree).

[0394] FIG. 15 shows a flowchart about the migration processing for the steered plane wave transmission. When the received signals are expressed by r(x,y,t), the received signals are expressed by r (x,y=0,t) at the aperture element array positions.

[0395] At first, as expressed by eq. (M2), the received signals are 2D Fourier's transformed regarding the time t and the lateral direction x (2D FFT can be used).

R(k_x,y=0,k)=∫∫r(x,y=0,t)exp{−i(k_xx+ωt)}dxdt  (M2)

Here, k=ω/c, the wavenumber k and the angular frequency ω are related using the proportional coefficient 1/c (one-to-one correspondence) and then, ω can be used instead of k to express the equations and to perform the calculations.

[0396] As mentioned above, special 2D FFT method can also be used and however, as a general (popular) method, at step 31, at first, the spectra of analytic signals are obtained by implementing FFT on the received signals regarding the time t at respective lateral coordinates x at the step S31. Besides, FFT is performed regarding the lateral direction x at the respective frequency coordinates within the bandwidth k (It is faster to calculate 2D spectra than the using eq. (M2) for calculating the respective 2D spectra).

[0397] When not performing the steered transmission of a plane wave, the above-mentioned calculations are performed and however, when performing the steering, the trimming is performed at the step S32, the results of the above-mentioned FFT on the time t (R′(x,0,k)) are multiplied with the complex exponential function (M3) (Similarly to the complex exponential function (11) used in the method (1), the multiplication of the FFT results on the time t and the complex exponential function can be performed at once and for such calculations, the exclusive FFT is also useful).

exp{ikx sin θ}  (M3)

[0398] Besides, at the step S33, FFT is implemented on the received signals in the lateral direction x. Here, the results are expressed as R″(k_x,0,k). Even if the trimming is programmed to be performed, a non-steered plane wave transmission can be processed (The steering angle can be set to zero degree).

[0399] In general, the wavenumber matching (or mapping) is performed next. When the beamforming to be performed is one of the methods (1) to (5) except for the general migration (the method (2) with no steering), similarly to using the modifications (conversions) about the propagation speed c and the coordinate (x_s,y_s) as likely expressed in eq. (M11) for the plane wave transmission, the respective modifications (conversions) of the propagation speed c and the coordinate system (x_s, y_s) for the respective beamformings into eqs. (E1) and (E2) are performed.

ĉ  (E1))

({circumflex over (x)}_s,ŷ_s)  (E2)

[0400] On the 2D Fourier's transform R″(k_x,0,k) calculated for the methods including the method (1), however, except for the general migration (the method (2) with no steering) or the above-mentioned R(k_x,0,k) calculated for the general migration, approximate interpolations (using the most neighborhood angular spectra at the digital frequency coordinate or bi-linear interpolations etc) are used to perform the wavenumber matchings respectively expressed by eqs. (M4) or (M4′).

$\begin{array}{cc}{F}^{″}\left(k_x,0,K\left(\right)\right)=R^{″}\left(k_x,0,k\right),\mathrm{where}K\left(\right)=\hat{c}\mathrm{sgn}\left(\right)\sqrt{k_x^2+2^{}},=\sqrt{{\hat{k}}^2-k_x^2}=\sqrt{{\left(\frac{\omega }{\hat{c}}\right)}^2+-k_x^2}\mathrm{or}\sqrt{{\left(\frac{k}{\alpha }\right)}^2-k_x^2},& \left(M4\right)\\ F\left(k_x,0,K\left(k_y\right)\right)=R\left(k_x,0,\mathrm{sk}\right),\mathrm{where}K\left(k_y\right)=c\mathrm{sgn}\left(k_y\right)\sqrt{k_x^2+k_y^2},k_y=\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2}=\sqrt{{\left(s\frac{\omega }{c}\right)}^2-k_x^2},& \left({\mathrm{M4}}^{\prime }\right)\end{array}$

[0401] when the received signals are reflected ones, s=2; and when transmission signals, s=1.

[0402] When the approximate interpolations are not performed on the wavenumber matchings expressed by eqs. (M4) and (M4′) the wavenumbers in the depth direction respectively expressed in the supplementary explanations of equations are used, whereas when the approximate interpolations are performed, the wavenumbers in the depth direction are respectively ones obtained by dividing the angular frequency ω by the converted propagation speed (E1) and c. These are also below.

[0403] The wavenumber matchings are performed in these ways, and the next function (M4″) is calculated.

F″(k_x,0,K({circumflex over (k)}_y)) or F(k_x,0,K(k_y))  (M4″)

Besides, using the function (M4″), the next eqs. (M5) and

[0404] (M5′) are calculated.

$\begin{array}{cc}\frac{\hat{c}}{\sqrt{k_x^2+2^{}}}F^{″}\left(k_x,0,K\left(\right)\right)& \left(M5\right)\\ \frac{{\mathrm{ck}}_y}{\sqrt{k_x^2+k_y^2}}F\left(k_x,0,K\left(k_y\right)\right)& \left({\mathrm{M5}}^{\prime }\right)\end{array}$

[0405] With respect to the respective eqs. (M5) and (M5′), by implementing 2D inverse Fourier's transforms regarding the wavenumber k_x and the wavenumbers (E3) as expressed by eq. (M6) and (M6′), image signal f(x,y) is generated.

$\begin{array}{cc}\mathrm{or}k_y& \left(E3\right)\\ f\left(x,y\right)=\int \int \frac{\hat{c}}{\sqrt{k_x^2+2^{}}}F^{″}\left(k_x,0,K\left(\right)\right)\exp \left\{\left(k_xx+y_s\right)\right\}k_x& \left(\mathrm{M6}\right)\\ f\left(x,y\right)=\int \int \frac{{\mathrm{ck}}_y}{\sqrt{k_x^2+k_y^2}}F\left(k_x,0,K\left(k_y\right)\right)\exp \left\{\left(k_xx+k_yy\right)\right\}k_yk_x& \left({\mathrm{M6}}^{\prime }\right)\end{array}$

[0406] The 2D inverse Fourier's transform of eqs. (M6) and (M6′) can be performed using 2D IFFT. Special 2D IFFT can also be used and however, as general (popular) methods for calculating eqs. (M6) and (M6′), with respect to the respective wavenumbers of k_x within the bandwidths of signals, IFFT can be performed regarding another respective wavenumbers of (E3) within the bandwidths of signals; and further with respect to the respective spatial coordinates y generated, IFFT can be performed regarding the respective wavenumbers of k_x within the bandwidths of signals (It is faster to calculate 2D image signals than the using eq. (M6) or (M6′) for calculating the respective 2D image signals).

[0407] In the nonpatent document 12, eq. (M6) using y_s in the equation is not disclosed and instead, it is disclosed that not y_s but y is used for the calculation and after the calculation, correction of the coordinate is performed. For the correction of coordinate, approximate interpolations are performed or no approximation interpolations are performed by performing the multiplications of complex exponential functions (a past invention of the inventor of present invention). Eq. (M6) can also be used when the steering angle is zero degree.

[0408] The instrument of present invention performs the wavenumber matchings together with the 2D inverse Fourier's transform or together with the inverse Fourier's transform in the depth direction, with no approximate interpolations. That is, on the 2D Fourier's transform R″(k_x,0,k) calculated for the methods including the method (1), however, except for the general migration (the method (2) with no steering), or the above-mentioned R(k_x,0,k) calculated for the general migration, as expressed by eqs. (M7) or (M7′), the integration regarding k is implemented with respect to the respective wavenumbers of k_x within the bandwidths of signals to simultaneously perform the wavenumber matching on the wavenumber (E3) and the inverse Fourier's transform (IFFT possible) in the depth direction (step S34) and after the integrations, the lateral (x) IFFT is performed.

f(x,y)=∫∫R″(k_x,0,k)exp{i(k_xx+{circumflex over (k)}_yy_s)}dkdk_x  (M7)

f(x,y)=∫∫R(k_x,0,exp{i(k_xx+k_yy)}dkdk_x  (M7′)

In nonpatent document 12, eq. (M7) using y_s in the equation is not disclosed. Eq. (M7) can also be used when the steering angle is zero degree. Similarly to the methods (1) to (6), after summing the spectral k components, the inverse Fourier's transform (IFFT) can be performed on the lateral wavenumber k_x and then, the inverse Fourier's transform is performed once and the total calculations are high speed.

[0409] Moreover, the migrations to be performed being different from the general migration (corresponding to the processing of non-steering of the method (2)), corrections of the lateral positions can be performed during performing the calculations of eq. (M6) or (M7). For instance, when performing the transmission of a steered plane wave of the method (1), at the step S34, at first, the calculation about the wavenumber (E3); at the step S35, the function (M8) calculated as each result is multiplied with complex exponential function (M9) for the position correction; at the step S36, IFFT is implemented on the wavenumber k_x in the lateral direction. Alternatively, instead of the steps S35 and S36, eq. (M9) can also be multiplied together with the complex exponential function used for the inverse Fourier's transform regarding the wavenumber k_x in the lateral direction, or the exclusive IFFT can also be implemented. Eq. (M9) can also be used for the zero steering angle. Thus, at the step S37, image signals f(x,y) are generated.

$\begin{array}{cc}{F}^{\mathrm{\prime \prime \prime }}\left(k_x,y\right)\mathrm{or}R^{\mathrm{\prime \prime \prime }}\left(k_x,y\right)& \left(M8\right)\\ \exp \left(k_xy\frac{\sin \theta }{2-\cos \theta }\right)& \left(M9\right)\end{array}$

Summarizing, using eq. (M6), (M7) or (M7′) yields a new processing for generating, with a high speed, image signal f(x,y) with no errors due to approximate interpolations.

[0410] Without performing the multiplication of eq. (M9) and with no approximate interpolations, to obtain the same results, eq. (M6) or (M7) is calculated using the next eq. (N4) instead of eq. (M4).

$\begin{array}{cc}{F}^{″}\left(k_x,0,K\left(\right)\right)=R^{″}\left(k_x,0,k\right)\mathrm{where}K\left(\right)=\hat{c}\mathrm{sgn}\left(\right)\sqrt{{\left(k_x-k\sin \theta \right)}^2+2^{}},=\sqrt{{\hat{k}}^2-{\left(k_x-k\sin \theta \right)}^2}=\sqrt{{\left(\frac{\omega }{\hat{c}}\right)}^2-{\left(k_x-k\sin \theta \right)}^2}\mathrm{or}\sqrt{{\left(\frac{k}{\alpha }\right)}^2-{\left(k_x-k\sin \theta \right)}^2}.& \left(\mathrm{N4}\right)\end{array}$

That is, when the approximate interpolations are not performed on the wavenumber matching, the wavenumber in the depth direction expressed in the supplementary explanation of equation is used, whereas when the approximate interpolations are performed, the wavenumber in the depth direction is one obtained by dividing the angular frequency ω by the converted propagation speed (E1).

[0411] The equation of wavenumber in the depth direction in these equations is similar to eq. (13) of the method (1). To generate the same result using the method (1), however, with no use of −k sin θ in kx−k sin θ in eqs. (13) to (15) (i.e., use as zero), as in the method (6) the inverse Fourier's transform being implemented on the multiplication with eq. (M9), eq. (16) can be multiplied with eq. (M9) prior to performing the processings mentioned in the paragraphs 0202 and 0203. However, note that the steering of the plane wave achieved by the above-mentioned method (6) is only realized under the approximate calculations and therefore, using eqs. (N4) and (M7) in the method (6) can perform the beamforming with no approximate interpolations and with a high accuracy, whereas the use of eq. (M9) decreases the accuracy of the method (1). Moreover, implementing the 2D IFFT for the last inverse Fourier's transform (as mentioned later, 3D IFFT in a 3D case) increases the calculation speed for the method (6), however, decreases the speed for the method (1) (The processing mentioned in the paragraph 0203 is high speed).

[0412] On the respective modified methods (1) and (6), when performing approximate interpolations on the wavenumber matchings, to generate the same results using eqs. (M9) and (N4), the equations of approximate interpolations change correspondingly (mentioned later in the respective (A) and (B) in the paragraph 0352).

[0413] On the respective modified methods (1) and (6), when performing approximate interpolations on the wavenumber matchings, to generate the same results using eqs. (11) and (M3) (using the steering angle data θ) or not (the steering angle θ is set to zero degree), the equations of approximate interpolations change correspondingly (mentioned later in the respective (A′) and (B′) in the paragraph 0352).

[0414] Beamforming using the plane wave transmission is applied to various beamformings as mentioned before in the present invention document and instead the processings mentioned in this paragraph can also be used. It is cautious that when the reception dynamic focusing is performed using the method (6) on arbitrary transmission beamformings such as the transmission focusing etc, as mentioned later, eq. (M3″), expressed using the wavenumber [eq. (M13)] expressed by the angular frequency ω and the converted propagation speed (E1), is used instead of eq. (M3) and then, for the wavenumber k in −k sin θ_t in the expression of approximate interpolation, eq. (M13) is required to be used instead.

[0415] On the respective methods (1) and (6), the methods mentioned in this paragraph can also be combined and performed. For instance, similarly to J.-y. Ku's method that performs approximate interpolations for the method (1) (paragraph 0195, expressions are described in (C′) in the paragraph 0352), all the wavenumber matchings of the method (6) can be performed via approximate interpolations and accordingly, the first 2D Fourier's transform and the last 2D inverse Fourier's transform can be performed using 2D FFT and 2D IFFT, respectively (Described in (D′) in the paragraph 0352. As mentioned later, in a 3D case, 3D FFT). In the respective these, eq. (11) can also be used (The steering angle dataθ is used) and eq. (M3) can also be used (Described in (C) and (D) in the paragraph 0352). Off course, non-steering can also be used.

[0416] As mentioned above, the plane wave transmission on the basis of the methods (1) and (6) can be applied to various beamformings.

[0417] Here, mainly explained is the use of the migration method to the method (1), i.e., a high speed beamforming with no approximate interpolations for a steered or non-steered plane wave transmission. All the beamformings described in other methods of the present invention, the method (2) (a monostatic SA method including a steering case), the method (3) (a multistatic SA method including a steering case), the method (4) (a transmission fixed focus with a steering or no steering), the method (5) (beamformings on the polar coordinate system or arbitrary orthogonal curvilinear coordinate systems) can also be performed similarly. On the transmission and the reception, different steering angles can also be processed similarly. Apodizations can also be performed similarly.

[0418] The 3D cases can also be processed similarly. When the received signals obtained using 2D aperture element array are expressed as r(x,y,z,t), the reception signals received at the position of aperture element array (y=0) are expressed as r(x,y=0,z,t).

[0419] At first, as shown in eq. (M′2), the reception signals are 3D Fourier's transformed with respect to the time t, the lateral direction x and the elevational direction z (3D FFT can be performed).

R(k_x,y=0,k_z,k)=∫∫r(x,y=0,z,t)exp{−i(k_xx+k_zz+ωt)}dxdt   (M′2)

[0420] where k=ω/c.

[0421] In general, the spectra R(x,0,z,k) of analytic signals are obtained for the reception signals by performing FFT regarding the time t. Besides, for the respective frequency coordinates k within the bandwidth of signals, FFT is implemented regarding the lateral (x) and elevational (z) directions to generate R(k_x,0,k_z,k) (It is faster to calculate 3D spectra than the using eq. (M′2) for calculating the respective 3D spectra).

[0422] When not performing the steered transmission of a plane wave, the above-mentioned calculations are performed and however, when performing the steering with the steering angle being an angle between the transmission direction as a plane wave and the axial direction (y) is expressed using zero or non-zero elevation (θ) and azimuth (ψ) angles, the trimming is required to be performed, the results of the above-mentioned FFT on the time t (R′(x,0,z,k)) are multiplied with the complex exponential function (M′3) (The multiplication of the FFT results on the time t and the complex exponential function can be performed at once and for such calculations, the exclusive FFT is also useful).

exp{ik sin θ(cos φx+sin φz)}  (M′3)

[0423] Besides, FFT is implemented on the received signals in the lateral direction x. Here, the results are expressed as R″(k_x,0,z,k). Even if the trimming is programmed to be performed, a non-steered plane wave transmission can be processed (The steering angle can be set to zero degree).

[0424] Next, the wavenumber matching (or mapping) is performed. When the beamforming to be performed is one of the methods (1) to (5) except for the general migration (the method (2) with no steering), the respective modifications (conversions) of the propagation speed c and the coordinate system (x_s,y_s,z_s) for the respective beamformings into eqs. (E′1) and (E′2) are performed.

ĉ  (E′1)

({circumflex over (x)}_s,ŷ_s,{circumflex over (z)}_s)  (E′2)

[0425] On the 3D Fourier's transform R″(k_x,0,z,k) calculated for the methods including the method (1), however, except for the general migration (the method (2) with no steering) or the above-mentioned R(k_x,0,z,k) calculated for the general migration, approximate interpolations (using the most neighborhood angular spectra at the digital frequency coordinate or bi-linear interpolations etc) are used to perform the wavenumber matchings respectively expressed by eqs. (M′4) or (M′4′).

$\begin{array}{cc}{F}^{″}\left(k_x,0,k_z,K\left(\widehat{k_y}\right)\right)=R^{″}\left(k_x,0,k_z,k\right)\mathrm{where}K\left(\widehat{k_y}\right)=\hat{c}\mathrm{sgn}\left(\widehat{k_y}\right)\sqrt{k_x^2+k_z^2+{\widehat{k_y}}^2},\widehat{k_y}=\sqrt{{\hat{k}}^2-k_x^2-k_z^2}=\sqrt{{\left(\frac{\omega }{\hat{c}}\right)}^2-k_x^2-k_x^2}\mathrm{or}\sqrt{{\left(\frac{k}{\alpha }\right)}^2-k_x^2-k_z^2},& \left(M^{\prime }4\right)\\ F\left(k_x,0,k_z,K\left(k_y\right)\right)=R\left(k_x,0,k_z,\mathrm{sk}\right)\mathrm{where}K\left(k_y\right)=c\mathrm{sgn}\left(k_y\right)\sqrt{k_x^2+k_z^2+k_y^2},k_y=\sqrt{{\left(\mathrm{sk}\right)}^2-k_x^2-k_z^2}=\sqrt{{\left(s\frac{\omega }{c}\right)}^2-k_x^2-k_z^2},& \left(M^{\prime }4^{\prime }\right)\end{array}$

[0426] when the received signals are reflected ones, s=2;

[0427] and when transmission signals, s=1.

[0428] When the approximate interpolations are not performed on the wavenumber matchings expressed by eqs. (M′4) and (M′4′), the wavenumbers in the depth direction respectively expressed in the supplementary explanations of equations are used, whereas when the approximate interpolations are performed, the wavenumbers in the depth direction are respectively ones obtained by dividing the angular frequency ω by the converted propagation speed (E′1) and c. These are also below.

[0429] The phase matchings are performed in these ways, and the next function (M′4″) is calculated.

F″(k_x,0,k_z,K({circumflex over (k)}_y)) or F(k_x,0,k_z,K(k_y))  (M′4″)

Besides, using the function (M′4″), the next eqs. (M′5) and (M′5′) are calculated.

$\begin{array}{cc}\frac{\hat{c}}{\sqrt{k_x^2+k_z^2+2^{}}}F^{″}\left(k_x,0,k_z,K\left(\right)\right)& \left(M^{\prime }5\right)\\ \frac{{\mathrm{ck}}_y}{\sqrt{k_x^2+k_z^2+k_y^2}}F\left(k_x,0,k_z,K\left(k_y\right)\right)& \left(M^{\prime }5^{\prime }\right)\end{array}$

[0430] With respect to the respective eqs. (M′5) and (M′5′), by implementing 3D inverse Fourier's transforms regarding the wavenumber k_x and k_z, and the wavenumbers (E′3) in the 3D case as expressed by eq. (M′6) and (M′6′), image signal f(x,y) is generated.

$\begin{array}{cc}\mathrm{or}k_y& \left(E^{\prime }3\right)\\ f\left(x,y,z\right)=\int \int \frac{\hat{c}}{\sqrt{k_x^2+k_z^2+2^{}}}F^{″}\left(k_x,0,k_z,K\left(\right)\right)\exp \left\{\left(k_xx+k_zz+y_s\right)\right\}k_xk_z& \left(M^{\prime }6\right)\\ f\left(x,y,z\right)=\int \int \frac{{\mathrm{ck}}_y}{\sqrt{k_x^2+k_z^2+k_y^2}}F\left(k_x,0,k_z,K\left(k_y\right)\right)\exp \left\{\left(k_xx+k_zz+k_yy\right)\right\}k_yk_xk_z& \left(M^{\prime }6^{\prime }\right)\end{array}$

[0431] The 3D inverse Fourier's transform of eqs. (M′6) and (M′6′) can be performed using 3D IFFT. Special 3D IFFT can also be used and however, as general (popular) methods for calculating eqs. (M′6) and (M′6′), with respect to the respective wavenumbers of k_x and k_z within the bandwidths of signals, IFFT can be performed regarding another respective wavenumbers of (E′3) within the bandwidths of signals; and further with respect to the respective spatial coordinates y generated, IFFT can be performed regarding the respective wavenumbers of k_x and k_z within the bandwidths of signals (It is faster to calculate 3D image signals than the using eq. (M′6) or (M′6′) for calculating the respective 3D image signals).

[0432] The instrument of present invention performs the wavenumber matchings together with the 3D inverse Fourier's transform or together with the inverse Fourier's transform in the depth direction, with no approximate interpolations. That is, on the 3D Fourier's transform R″ (k_x,0,k_z,k) calculated for the methods including the method (1), however, except for the general migration (the method (2) with no steering), or the above-mentioned R(k_x,0,k_z,k) calculated for the general migration, as expressed by eqs. (M′7) or (M′7′), the integration regarding k is implemented with respect to the respective wavenumbers of (k_x,k_z) within the bandwidths of signals to simultaneously perform the wavenumber matching on the wavenumber (E′3) and the inverse Fourier's transform (IFFT possible) in the depth direction and after the integrations, the lateral (x) and elevation (z) IFFTs are performed.

f(x,y,z)=∫∫R″(k_x,0,k_z,k)exp{i(k_xx+k_zz+{circumflex over (k)}_yy_s)}dkdk_xdk_z  (M′7)

f(x,y,z)=∫∫R(k_x,0,k_z,k)exp{i(k_xx+k_zz+k_yy_s)}dkdk_xdk_z  (M′7′)

[0433] In nonpatent document 12, eqs. (M′6) and (M′7) using y_s in the equation are not disclosed. Both equations can also be used when the steering angle is zero degree. Similarly to the methods (1) to (6), after summing the spectral k components, the inverse Fourier's transforms (IFFTs) can be performed on the lateral (k_x) and elevational (k_z) wavenumbers and then, the inverse Fourier's transform is performed once and the total calculations are high speed.

[0434] Moreover, the migrations to be performed being different from the general migration (corresponding to the processing of non-steering of the method (2)), corrections of the lateral (x) and elevational (z) positions can be performed during performing the calculations of eq. (M′6) or (M′7). For instance, when performing the transmission of a steered plane wave of the method (1), at first, the calculation about the wavenumber (E′3); and next, the function (M′8) calculated as each result is multiplied with complex exponential function for the position correction; and finally, IFFTs are respectively implemented on the wavenumbers k_x and k_z in the lateral and elevational directions.

F′″(k_x,y) or R′″(k_x,y)  (M′8)

Summarizing, using eq. (M′6), (M′6′), (M′7) or (M′7′) yields a new processing for generating, with a high speed, image signal f(x,y, z) with no errors due to approximate interpolations.

[0435] Without performing the multiplication of the complex exponential function corresponding to eq. (M9) and with no approximate interpolations, to obtain the same results, eq. (M6) or (M7) is calculated using the next eq. (N′4) instead of eq. (M′4).

$\begin{array}{cc}F^{″}\left(k_x,0,k_z,K\left(\right)\right)=R^{″}\left(k_x,0,k_z,k\right),\mathrm{where}K\left(\right)=\hat{c}\mathrm{sgn}\left(\right)\sqrt{{\left(k_x-k\sin \theta \cos \varphi \right)}^2+{\left(k_z-k\sin \mathrm{\theta sin}\varphi \right)}^2+2^{}},\begin{array}{c}=\sqrt{{\hat{k}}^2-{\left(k_x-k\sin \theta \cos \varphi \right)}^2-{\left(k_z-k\sin \theta \sin \varphi \right)}^2}\\ =\sqrt{{\left(\frac{\omega }{\hat{c}}\right)}^2-{\left(k_x-k\sin \theta \cos \varphi \right)}^2-{\left(k_z-k\sin \theta \sin \varphi \right)}^2}\end{array}\mathrm{or}\sqrt{{\left(\frac{k}{\alpha }\right)}^2-{\left(k_x-k\sin \theta \cos \varphi \right)}^2-{\left(k_z-k\sin \theta \sin \varphi \right)}^2}.& \left(N^{\prime }4\right)\end{array}$