Light and Particle Image Intensifier

1. Field of the Invention

This invention relates generally to imaging devices and more particularly to a device for detecting image conveying light or particles ("beam") and transmitting to data processing and video equipment information needed by that equipment to display on a CRT the image carried by the beam.

2. Description of the Prior Art

Generally, two types of devices have been used to produce images from particle or light sources--devices producing images on photographic film and image intensifiers. Although an image having good resolution can be obtained on light-sensitive film, the time required to process the film is relatively long and prohibitive for many applications. Further, a dynamic image of the object under examination cannot be obtained through the use of light-sensitive film.

Although an image of an object can be obtained quickly using conventional image intensifiers, the resolution of the image (4 line pairs/mm) is unacceptable for many applications. For example, the medical profession generally considers X-ray images having only 4 line pairs/mm resolution to be unacceptable as an aid in examining the human body, and so conventional X-ray image intensifiers have not been heavily relied upon as a means for obtaining X-ray images of portions of the human body.

Finally, conventional X-ray equipment, including equipment employing X-ray sensitive film and X-ray image intensifiers, has been large and cumbersome and, therefore, has placed severe restrictions on the use of such equipment.

A light and particle ("beam") immage intensifier and a self-scanning charge-coupled device are provided that transmit quickly to data processing and video equipment information from which the image conveyed by the beam can be created and displayed. The image created by the present invention has a high resolution (approximately 10 line pairs/mm). The present invention also provides a dynamic image which is useful for examining moving objects. The present invention is compact and can be as thin as 2 to 3 inches.

The charge-coupled device disclosed herein can be used to detect particles directly and to transmit to data processing and video equipment information by which that equipment can reconstruct and display the image conveyed by such sources.

Although the present invention can be used to create and display an image conveyed by any type of light or particle source, it is particularly useful as an X-ray image intensifier. The high resolution of the image created by the present invention renders it useful as an aid to physicians and surgeons for examining the human body, to industry for examining structures for defects and to astronomers. One embodiment of the present invention provides an image intensifier that is approximately 6 inches in diameter and 2 inches thick and can be located on the under side of an operating table. Such an application allows a surgeon to view a dynamic image of any portion of a human body located on the table as the surgeon operates. The present invention is also useful to dentists since it can be as small as 3/4 of an inch in diameter or smaller.

Further, the present invention can be used not only to create an image from an image conveying light or particle source but to accept external electrical signals and create an image therefrom. An example of such a device is an X-ray image intensifier that can receive gray-scale information from an ultrasonic transmitter/receiver and can convey that information to the same data processing and video equipment that is used to process the X-ray image information.

One embodiment of the present invention includes a scintillator/photocathode unit, a charge-coupled device ("CCD") and apparatus for imposing an electric field between the photocathode and CCD. The incident image conveying beam is converted to photoelectrons by the scintillator/photocathode unit. The photo-electrons are accelerated by the electric field and impact the sensing areas of the CCD, which is operating in the front electron bombardment mode. Information relating to the location and intensity of the charges created by the electrons impacting the sensing areas is conveyed by the CCD to the data processing and video equipment. This information is sufficient to permit the data processing and video equipment to construct and display the image conveyed by the incident beam. Alternately, a micro channel plate can be disposed between the photocathode and the CCD. The micro channel plate (MCP) improves the resolution of the image by channeling the electrons into a large number of relatively discrete streams and increases the contrast of the image by increasing the number of electrons impacting the sensing areas. If it is desired to use the CCD in the photon bombardment mode, a phosphor screen can be disposed in front of the CCD to convert the electrons to photons. Moreover, external image conveying electrical signals may be input to the CCD and passed to the data processing and video equipment and an image can be created therefrom. When the CCD is used in the electron bombardment mode, the areas of the CCD that are exposed to the electrons, other than the sensing areas, are shielded so that those areas do not become damaged by the electron stream.

In an alternate embodiment of the present invention, a silicon diode target is used instead of the CCD to intercept the electrons emitted by the photocathode and an electron beam gun scans the target to detect information relating to the presence and location of charges created on the target by the intercepted electrons and passes that information to the data processing and video equipment. An MCP is disposed between the photocathode and the target to provide improved sensitivity for the device.

Alternately, a target grid and photoanode can be used to detect the presence and location of the electrons emitted by the photocathode. The target grid scans the electrons flowing from the MCP by selectively and systemically allowing portions of the stream to pass through one window of the grid at a time. These portions impact the photoanode and the photoanode passes the information relating to intensity and location of the electrons to the data processing and video equipment.

It should be noted that the scintillator should be eliminated when the image intensifier is used to detect visible light.

The scintillator, photocatode and MCP and not needed if it is desired to use the CCD to detect particles directly.

In this application, the term "light" shall be construed to include X-ray radiation, visible light, gamma-ray radiation, ultraviolet light and infra-red light. The term "MCP" shall be construed to mean a micro channel plate. The term "charge-coupled device" or "CCD" shall be construed to mean a self-scanning charge-coupled device. The term "charge-coupled device" or "CCD" shall be construed to mean a conventional charge coupled device with register areas protected from atomic particles when the CCD is used to detect atomic particles, any conventional CCD or a conventional CCD with memory capability when the CCD is used in an intensifier that processes X-rays, and a conventional CCD with storage capability when the CCD is used in the photon bombardment mode. The terms "incident beam" and "beam" shall be construed to mean incident light and particles. The term "particle" shall include photons and atomic particles. The term "electrical signal" shall include analog and digital signals.

To enhance the understanding of the detailed description of the preferred embodiment below, reference may be had to the drawing in which:

FIG. 1 is a schematic diagram of an image intensifier constructed according to the provisions of the present invention that includes a scanning grid as an electron detector;

FIG. 2 is a schematic view of a portion of the scanning grid shown in FIG. 1;

FIG. 3 is a schematic diagram of an image intensifier constructed according to the provisions of the present invention that includes a silicon diode target and an electron beam gun as an electron detector;

FIG. 4 is a schematic diagram of an image intensifier constructed according to the provisions of the present invention that includes a CCD as an electron or photon detector;

FIG. 5 is a schematic diagram of an image intensifier constructed according to the provisions of the present invention that employs a potential field rather than an MCP for improving system resolution;

FIG. 6 is a schematic diagram of the sensing, storage and register areas of one unit of a CCD that can be constructed according to the provisions of the present invention; and,

FIG. 7 is an electrical equivalent circuit of the sensing and storage areas of a CCD that can be constructed according to the provisions of the present invention.

FIG. 1 depicts a light or particle image intensifier 10 that includes a scanning grid 24 and a photoanode 25 for detecting electrons 22. An incident beam 12 impacts scintillator 14 thereby causing photons (not shown) to impact photocathode 16. Photocathode 16 can be any photocathode suitable for converting photons to photoelectrons. Scintillator 14 produces photons of a wavelength such that a maximum quantity of photo-electrons 18 are produced by photocathode 16 when it is impacted by a photon emitted by scintillator 14. The material comprising the scintillator can be matched to the type of beam to be detected. To detect X-rays, gamma-rays, infra-red light ultraviolet light and atomic particles the scintillator should be made of any of the materials listed below:

NaI (Tl)

CsI (Tl)

CsI (Na)

CaF.sub.2 (Eu)

.sup.6 Li (Eu)

TlCl (BeI)

CsF

BaF.sub.2

Bi.sub.4 Ge.sub.3 O.sub.12

Ki (Tl)

CaWO.sub.4

CdWO.sub.4

If visible light is to be detected, the scintillator should be eliminated.

Photoelectrons 18, emitted by photocathode 16, are accelerated by an electric potential (not shown) established between photocathode 16 and a conventional MCP 20 and enter MCP 20. The electric field between photocathode 16 and MCP 20 can be approximately 300 volts. Preferably a 1 KV to 2 KV field is imposed across MCP 20 in which case MCP 20 multiplies the number of photoelectrons entering MCP 20 by 10.sup.4 to 10.sup.6. Secondary electrons 22, emitted from MCP 20, are accelerated by an electric field established between MCP 20 and a scanning grid 24 and travel toward scanning grid 24. The electric potential between MCP 20 and grid 24 can be approximately 300 V. A portion of scanning grid 24 is shown in FIG. 2. Scanning grid 24 is composed of vertical leads 28 disposed in a position such that they are in contact with horizontal leads 30 and form grid windows 32. Vertical leads 28 are electrical insulated from horizontal leads 30 in any suitable fashion and are energized by a suitable electric source. A grid window 32 allows electrons 22 to pass through grid 24 (e.g. electrons 26 in FIG. 1) only if all four leads forming its boundaries are of the same polarity. If the leads forming a window 32 have two different polarities, the electrons will not be passed by the window but will be absorbed by the grid. It can be seen, therefore, that the beam of electrons 22 can be systematically scanned by permitting only one window (such as window 34) at a time to have boundaries of the same polarity and to change that window in a systematic fashion. Electrons 26 impact a conventional photoanode 25 which passes the information contained in each passed beam 26 relating to position and intensity of electrons 22 in any known fashion to data processing and video equipment (not shown) where an image is produced and displayed on a CRT. An electric field is established in any suitable fashion for accelerating the passed electrons 26 toward the photoanode 25. That field can be 100 volts. An electric field of 1 KV-2 KV can be set up across MCP 20 to facilitate the production of secondary electrons 22 by MCP 20.

FIG. 3 shows another embodiment 40 of the present invention which is similar to image intensifier 10 but which detects electrons 22 by using silicon diode target 42 and electron beam gun 44 instead of a scanning grid and photoanode. Electrons 22 impact on target 42 and create charges in the target 42. A conventional electron beam gun 44 scans target 42 with an electron beam 46. The charges created by electrons 22 impacting on target 42 are detected by beam 46 and information relating to the location and intensity of the charges is transmitted in any known fashion to the data processing and video equipment from which an image is constructed and displayed. Again an electric field of approximately 1 KV should be established in any known fashion between MCP 20 and target 42 to accelerate electrons 22 toward target 42. An electric field of approximately 20 KV should be set up between target 42 and electron gun 44.

Another preferred embodiment 50 is shown in FIG. 4. This embodiment is similar to image intensifiers 10 and 40, but detects electrons 22 by a self-scanning CCD 52 (see FIGS. 6 and 7). An electric field of 300 volts is established between MCP 20 and CCD 52. CCD 52 can be a device, such as a semiconductor chip, having sensing and register areas common to conventional CCDs but having the additional feature of storage areas for storing information sensed by the sensing areas, for passing such information to the register areas and for accepting image-conveying external analog electrical inputs from sources other than the sensing areas (such as the register areas). Alternately, CCD 52 can be a conventional CCD having only sensing and register areas. Sensing areas 54 detect electrons 22. Electrons 22 impacting sensing areas 54 create charges on the photo diode sensors 60 formed therein (see FIG. 7). These charges are transferred to the register areas 58 of the CCD. If a CCD having storage areas is desired, areas 58 of CCD 52 contain those storage areas. The equivalent circuit for each sensing and storage area is shown schematically in FIG. 7. When switch S1 is in position 1, sensor diode 60 is being charged by source V.sub.DD preparatory to detecting electrons 22; switch S2 can be placed in position 2 to transfer information contained in the storage area to the register area through field effect transistor F2 or it can be in position 1 whereby no transfer takes place. When switch S1 is in position 2, switch S2 can be placed in position 2 and information from the register area can be read into the storage area through field effect transistor F1. Also, when switch S1 is in position 2, sensing diode 60 can detect the presence of electrons 22. When switch S1 is in position 3, information is moved from sensing diode 60 to the storage area. Capacitor C1 allows information to flow from the storage area to the register area non-destructively. The length of time during which information can be stored in the storage areas is limited only by the leakage rate of capacitor C1. As long as capacitor C1 is charged, F2 can be triggered and information can be passed from the storage area to the register area. When image intensifier 50 is being used to create an image conveyed by light or particles, the sequence of switching is as follows:

1. S1 in position 1 (sensor charging), S2 in position 1

2. S1 in position 2 (sensor reading), S2 in position 1

3. S1 in position 3 (transfer from sensor to storage), S2 in position 1

4. S1 in position 1 (sensor charging), S2 in position 2 (transfer from storage to register) (sensor ready)

5. Read out register areas to data processing and video equipment

6. Repeat steps 2., through 6.

FIG. 6 depicts schematically one unit 80 of the CCD array 52. Units 80 are bonded together in any suitable fashion to form CCD array 52. The sensing areas of unit 80, S1 to SN, pass information to the storage areas, M1 to MN. Storage areas M1 to MN pass information to output register areas R1 to RN. The register areas are read out or "scanned" in serial fashion to the data processing and video equipment. The scanning sequence is as follows:

1. Move R1 to R2, R2 to R3, . . . , RN-1 to RN, RN to data processing

2. Move R2 to R3, . . . , RN-1 to RN, RN to data processing

X. Move RN-2 to RN-1 to RN, RN to data processing

X+1. Move RN-1 to RN, RN to data processing

X+2. Move RN to data processing.

Alternately, the information in register area RN is moved to register area R1 each time it is moved from RN to the data processing equipment. This feature not only allows unit 80 to retain the information read out from the register units, but allows information to be read into the register areas from an external buffer. Each time information is read from register area RN, it is combined with the corresponding information from all the register areas RN of the other array units 80 to obtain one line of the image. Preferably, since the storage area can be read nondestructively, after step 4 above, switch S2 can alternate between positions 1 and 2 until the sensing diode is charged and new information sensed thereby. The sequence of switching would be as follows:

1. S1 in position 2 and S2 in position 1

2. S1 in position 3 and S2 in position 1

3. S1 in position 1 and S2 in position 2 (transfer from storage to register area)

4. Read out register areas

5. S2 in position 1

6. S2 in position 2

7. Read out register areas

8. S2 in position 1

9. S2 in position 2

10. Read out register areas

X. S1 in position 2 and S2 in position 1

X+1. S2 in position 2

X+2 Read out register areas

Y. S1 in position 3 and S2 in position 1.

Y+1. Repeat steps 2 through Y+1.

This sequence ensures that the displayed image will appear continuous. It is preferable that 9 readouts of the register area occur for every read by the sensing area. It can be seen that a similar sequence can be used when images are created from the external analog input.

Moreover, it is preferable that register area 1 (see FIG. 6) be able to receive information from an external source. This would enable the register areas to accept information from an external source and read that information into the storage areas via switch S2.

A CCD 52 having sensing, storage and register areas can be constructed using any of the well-known procedures for producing chips. The CCD 52 can transfer information between the sensing and storage areas, the storage and register and among the register areas in the same fashion that information is transferred within conventional CCDs.

Another preferred embodiment 70 of the present invention is shown in FIG. 5. This embodiment is identical to image intensifier 50, except that a 20-27 KV electric field is used to improve electron gain instead of an MCP.

It should be noted that visible light can be detected directly by CCD 52 and, accordingly, scintillator 14 or scintillator 14, photocathode 16 and MCP 20 can be eliminated (see FIGS. 4 and 5).

The components of the present invention that must be enclosed in a glass vacuum envelope can be so enclosed in any known fashion. Electrical communication between the enclosed components and external equipment can be accomplished in any known fashion. The scintillator may be disposed inside or outside the glass envelope. If it is desired to bombard the CCD with atomic particles, the CCD should be disposed inside the glass envelope. If it is desired to bombard the CCD with photons, the CCD can be disposed inside or outside the glass envelope.

The following list sets forth preferred specificatons for the present invention:

Size of one channel of MCP--40 microns

Distance between photocathode and MCP--1 to 2 mm

Distance between photocathode and CCD--10 to 20 mm

Distance between MCP and CCD--1 to 2 mm

Distance between MCP and scanning grid--10 mm

Distance between scanning grid and photoanode--10 mm

Distance between MCP and silicon diode target--1 to 2 mm

Distance between silicon diode target and electron beam gun--10-15 inches

Number of channels in MCP for 6 inch sensor--6 M

Size of each scanning grid window--40 microns

Amount of voltage on scanning grid leads--approximately 40 Volts

Potential across MCP to achieve gain of 10.sup. -2 KV.