Ultrasonic Imaging Apparatus

This invention relates to an ultrasonic imaging apparatus and, in particular, to an ultrasonic imaging apparatus for use in medical diagnosis.

An ultrasonic imaging apparatus is known which is adapted to scan a human subject with an ultrasonic beam emitted from an ultrasonic transducer, comprised of an array of ultrasonic transducer elements, to process the echo signals obtained and to display them, as a tomographic image, on the screen of a monitor. This type of ultrasonic imaging apparatus is utilized as an ultrasonic diagnosis apparatus in the practice of medicine.

In the aforementioned ultrasonic imaging apparatus, since the time taken from the transmission of the ultrasonic wave to the reception of echo signals is necessarily above a given value due to the speed of sound travelling through the living body, a requisite time of one cycle including a dwell time from one transmission/reception cycle to the next transmission becomes considerably longer, placing an inherent limitation on the obtainment of a tomographic image in real time. In order to effectively utilize the requisite time of one cycle, two reception circuits are provided in a parallel fashion so that two kinds of reception signals are obtained from a single ultrasonic transmission so as to substantially form a double scanning line. This type of apparatus is disclosed, for example, in Japanese Patent Publication (KOKOKU) No. 56-20017.

With this method, two sound waves, each corresponding to a composition of one-direction transmission sound field and each of two reception sound fields, are detected as two echo waves. As the distance of the two reception beams becomes greater, both sound fields are displaced in a different direction, thus leading to a lowering in their reception sensitivity and a variation in their beam widths.

It is accordingly the object of this invention to provide an ultrasonic imaging apparatus which can increase the number of raster lines or frames without producing a lowering of reception sensitivity and variation of the beam width.

According to this invention, an ultrasonic imaging apparatus is provided which can radiate at least two ultrasonic beams at a time in different directions and can obtain two corresponding echo signals in the same direction.

Furthermore, according to this invention, a group of odd-numbered ultrasonic elements and group of even-numbered ultrasonic elements are so driven as to radiate ultrasonic beams in different directions, and echo waves obtained in the same directions are converted to echo signals. These echo signals are subjected to signal processing and the resultant signals are displayed, as two raster lines, on a monitor.

FIG. 1 is a block circuit diagram showing an ultrasonic imaging apparatus according to one embodiment of this invention;

FIG. 2 shows two ultrasonic beams in a sector scan mode which are obtained from the apparatus of FIG. 1;

FIG. 3 is a block circuit diagram showing a major section for explaining the operation of the ultrasonic imaging apparatus of FIG. 1;

FIG. 4 is a view showing the direction in which an ultrasonic beam is radiated from another modification of the aforementioned ultrasonic imaging apparatus;

FIG. 5 shows a sector scan mode when Doppler components are obtained; and

FIG. 6 is a block circuit of the ultrasonic imaging apparatus including a Doppler detector.

In FIG. 1, ultrasonic transducer 5 is comprised of a plurality of ultrasonic transducer elements arranged in one direction, for example, an array of ultrasonic transducer elements 5-1 to 5-8. Odd numbered ultrasonic transducer elements 5-1, 5-3, 5-5 and 5-7 are connected to the output terminals of first transmitter 4a and even numbered ultrasonic transducer elements 5-2, 5-4, 5-6 and 5-8 are connected to the output terminals of second transmitter 4b.

In a transmitting system, ultrasonic transducer elements 5-1 to 5-8 are connected to the output terminals of first and second transmitters 4a and 4b. First and second transmitters 4a and 4b have drive pulse generators which output drive pulses for driving the corresponding ultrasonic transducer elements.

The input terminals of first and second transmitters 4a and 4b are connected to the output terminals of first and second transmission delay circuits 3a and 3b, respectively, and delay circuits 3a and 3b provide delay times corresponding to the radiation directions of ultrasonic beams to first and second transmitters 4a and 4b, respectively.

The output terminals of first and second delay data output circuits 2a and 2b in transmission delay data generator 2 are connected to the input terminals of first and second transmission delay circuits 3a and 3b, respectively, and the output terminal of reference clock generator 1 is connected to the input terminals of first and second transmission delay circuits 3a and 3b. First and second delay data output circuits 2a and 2b in transmission delay data generator 2 send delay data to first and second transmission delay circuits 3a and 3b, respectively, in synchronization with the clock pulses.

In a reception system, the output terminals of ultrasonic transducer 5 are connected to the input terminals of preamplifier section 6 including preamplifiers for amplifying the output signals of ultrasonic transducer elements 5-1 to 5-8.

The output terminals of preamplifier section 6 are connected to first and second receiver delay circuits 7a and 7b. First and second receiver delay circuits 7a and 7b include delay elements for delaying echo signals in accordance with transmission delay times. Receiver delay circuits 7a and 7b have their delay times set by the delay data of delay data output circuits 9a and 9b in receiver delay data generator 9.

The output terminals of first and second receiver delay circuits 7a and 7b are connected to display monitor 10 through display circuit 8.

When a sector scanning operation is performed on the ultrasonic imaging apparatus of FIG. 1, two ultrasonic beams LTl and LT2 are radiated at a time from ultrasonic transducer 5. In this case, as shown in FIG. 3, the odd numbered ultrasonic transducer elements 5-1, 5-3, 5-5 and 5-7 are so driven as to focus their ultrasonic beams at a point (focal point) Fl and the even numbered ultrasonic transducer elements 5-2, 5-4, 5-6 and 5-8 are so driven as to focus their ultrasonic beams at a point (focal point) F2. To this end, transmission delay data generator 2 outputs such delay data as to obtain the focal points F1 and F2. First and second delay circuits 3a and 3b, upon receipt of transmission delay data, deliver the corresponding data to first and second transmitters 4a and 4b.

First transmitter 4a drives the odd numbered ultrasonic transducer elements 5-1, 5-3, 5-5 and 5-7 in a time delay fashion to obtain the focal point Fl and second transmitter 4b drives the even numbered ultrasonic transducer elements 5-2, 5-4, 5-6 and 5-8 in a time delay fashion to obtain the focal point F2.

Ultrasonic transducer elements 5-1 to 5-8, upon receipt of echoes, convert them to echo signals. Preamplifier section 6, upon receipt of the echo signals, sends them to first and second receiver delay circuits 7a and 7b after they have been amplified. Delay circuits 7a and 7b subject the echo signals to a delay processing in accordance with the transmission delay times involved. In order to correct a positional discrepancy between the ultrasonic beam obtained by a group of odd-numbered ultrasonic transducer elements at the time of transmission and the ultrasonic beam obtained by the array of all ultrasonic transducer elements at the time of reception, the reception delay time is set so that the reception beam coincides with a raster line LR1 for the focal point F1. A transmission/reception beam LD1 is formed as a composite beam of raster lines LT1 and LR1.

Similarly, the reception delay time is set so that the reception beam coincides with a raster line LR2 for the focal point F2 and a transmission/reception beam LD2 is formed as a composite beam of the raster lines LT2 and LR2. It is to be noted that a discrepancy in position between the transmission and reception waves is 1/2 pitch for the ultrasonic elements.

The echo signals which are delay-processed by first and second receiver delay circuits 7a and 7b are supplied to display circuit 8 which includes, for example, a detector or a digital scan converter. Display circuit 8 converts the echo signals to television signals and sends them to display monitor 10. Monitor 10 displays two lines of beams at a time, as shown in FIG. 2.

In this way, scanning is performed, while two beams are being formed at a time, to allow a tomographic image to be displayed on monitor. That is, one frame is displayed with double the number of raster lines, thus improving the image resolution. In this case, two lines of rasters may be displayed during a sequential scan or displayed in a manner to put one line of raster between two lines of scans, as indicated by a broken line in FIG. 2. Furthermore, if the number of raster lines given for one frame is the same as that of a conventional device, it is possible to display two frames during one frame scanning period. That is, for the initial half scanning period, one frame is provided by two lines of scan and for the next half scanning period another frame is provided in a similar way. That is, if a display is made with the number of frames given for a predetermined time period, the number of raster lines is doubled and, on the other hand, with the number of raster lines given for an identical time period the number of frames is doubled.

In the aforementioned embodiment, the discrepancy in position between the transmission and reception signals is corrected through control of delay times. This control can be made by the following method.

As shown in FIG. 4, transmission beams involved at the odd-numbered transducer elements are set in the direction of LT1' which is the same as the direction LT1 of the transmission beam in the aforementioned embodiment. The echo beams are received only at transducer elements 5-3, 5-5 and 5-7, in which case the echo beams are set in the LR1' direction. In this case, a composition beam LD1' between the reception beam LT1' and the echo beam LR1' is set at a boundary of two middle transducer elements 5-4 and 5-5.

Similarly, the transmission beams involved at even-numbered transducer elements 5-2, 5-4, 5-6 and 5-8 are set in the LT2' direction which is the same as the LT2 direction of the transmission beams in the aforementioned embodiment. On the other hand, the echo beams are received only at transducer elements 5-4, 5-6 and 5-8, in which case the echo beams are set in the LR2' direction. Thus a composition beam LD2' of the reception beam LT2' and echo beam LR2' is set at a boundary of two middle transducer elements 5-4 and 5-5.

That is, a deflection support point for two composition beams LD1' and LD2' coincides with the boundary of two middle transducer elements in ultrasonic transducer 5 to provide a complete sector between two composition beams LD1' and LD2'.

Where transducer 5 is driven in an attempt to obtain a beam as shown in FIG. 4, first and second transmitters 4a and 4b drive ultrasonic transducer 5 at the transmission system as in the first-mentioned embodiment. In the reception system, first and second receiver delay circuits 7a and 7b subject transducer elements 5-3, 5-5 and 5-7 and 5-4, 5-6 and 5-8, to a delay processing as in the case of the first-mentioned embodiment.

The ultrasonic imaging apparatus of this invention can detect Doppler information and be applied to color Doppler display. In this case, of a pair of beams (LD1, LD2), one beam LDl is used for sector scanning and the other beam LD2 scans the same spot a plurality of times in an attempt to obtain the Doppler shift. That is, as shown in FIG. 5, the beam LDl sequentially scans the scan areas and the beam LD2 scans the same spot a plurality of times, for example, 8 times. The echo signals obtained by the beam LD2 are supplied to Doppler detector 20 through delay circuit 7 as shown in FIG. 6 and Doppler shift components are detected from the echo signals which have been obtained by eight scans. The Doppler shift components are supplied to digital scan converter 21 in display circuit 8, where they are converted to a color television signal. On the other hand, the echo signal for a tomograph, i.e., the output signal of delay circuit 7 is supplied to digital scan converter 21 to convert it into a television signal. Monitor 10, upon a receipt of the Doppler color signals, displays, in addition to a tomographic image, a Doppler color image.

This invention can effectively be applied to the case where an image signal is obtained through the scanning of the same spot a plurality of times as in the color display of the Doppler components.

Although, in the aforementioned embodiment, two ultrasonic beams have been explained as being transmitted at a time, three or more ultrasonic waves may be transmitted at a time, in which case ultrasonic transducer elements may be driven, for example, at two or three time intervals.