JPH0539506Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a one-dimensional or two-dimensional image sensor for X-rays.

B. Prior Art Conventionally, a photographic method using a silver-halogen emulsion has been used to obtain an X-ray image. However, this method requires development processing, which makes the development operation troublesome and
The disadvantage is that it takes time to see the line image. In recent years, an X-ray imaging plate using a stimulable phosphor has been developed for digitalizing X-ray photography and reducing the dose. This is X for the stimulable phosphor.
When a ray image is projected and stored and then scanned with a light beam, fluorescence corresponding to the X-ray image is emitted from the area irradiated with the light beam, and this fluorescence is sent to a photomultiplier tube using an optical fiber and sent as an electrical signal. and stores it in memory. This method has the advantage of being able to obtain an X-ray image immediately without the need for a wet development process, and that it can obtain an X-ray image with a lower dose of radiation compared to conventional photography methods. From the standpoint of safety, even lower doses are desired.

In the X-ray imaging plate method using the stimulable phosphor described above, the fluorescence emitted from the stimulable phosphor is collected and converted into an electrical signal, but all the fluorescence emitted from the phosphor is guided to the photoelectric conversion unit. In other words, the reproduction efficiency of the X-ray image accumulated in the phosphor is low, which causes a decrease in sensitivity and a decrease in dynamic range. For this reason, an X-ray image pickup device using an exo substance has been proposed. That is, an electron image is recorded by projecting an electron image onto an exo material layer, and by scanning this exo layer with a light beam, electrons corresponding to the incident electron dose are emitted and a video signal is obtained. A scintillator converts the light into light, a photocathode converts the light into electrons, a channel plate multiplies the electrons, and the electrons enter the exo material layer to accumulate an electron image.The exo material layer is scanned with a light beam. The image signal is extracted from the exo material layer, and the sensitivity is improved by multiplying the electrons in the channel plate.

C. Problems to be solved by the invention The above-mentioned method using exo materials involves a step of electron multiplication using a channel plate, which improves sensitivity and expands the dynamic range. In order to reduce the amount of X-ray irradiation on the human body, which is a subject, it is desired that X-ray image pickup apparatuses have further improved sensitivity. Therefore, the present invention aims to further improve the sensitivity of the X-ray imaging device using the above-mentioned exo substances.

D. Means for solving the problem Utilizing the property of an exo material to memorize the irradiated electron dose at its irradiation position and emit electrons according to the memorization upon light irradiation, a photocathode is closely formed on the scintillator layer. , a pixel-divided electron multiplication channel plate is placed behind the photocathode, an exo material film is placed behind the electron multiplication channel plate, and a light beam scans this exo material film from the back. The electrons emitted from the exo material film are made to enter the channel plate from the opposite direction, and the electrons emitted from the photocathode side of the channel plate are sent to the photocathode or between the photocathode and the channel plate. The video signal was captured by arranged electrodes and extracted.

E. Effect The scintillator layer and the photocathode are closely formed to form an X-ray sensitive film, and when an X-ray image is projected onto this film surface, the incident X-rays are converted into light at that position, and the light is immediately emitted at that position. The photoelectrons are converted into photoelectrons at the photocathode and emitted from the back surface, and the emitted photoelectrons are multiplied by the electron multiplication channel plate and enter the exo material film behind the channel plate, where they are exposed to X.
Accumulate line images. Next, when this exo material film is scanned from behind with a laser beam, electrons are emitted from the exo material film according to the accumulated image, and these electrons pass through the channel plate described above in the opposite direction, during which they are multiplied again. be done. These electrons are collected by a grid placed between the channel plate and the scintillator photocathode and stored in a memory as an electronic signal.

According to the above configuration, X-rays are converted into photoelectrons, and the photoelectrons are attracted and accelerated by the electric field and enter the channel plate, so there is no conversion loss like the optical loss when guiding fluorescence to a photoelectric converter with an optical fiber. Furthermore, the photoelectrons obtained in this way are multiplied by the channel plate twice using exo materials and converted into electrical signals, resulting in a high S/N ratio and low radiation dose. This is remarkable, and a wide dynamic range can be obtained by improving the S/N ratio.

F. Embodiment FIG. 1 shows a cross section of an embodiment of the present invention. In the figure, X-rays are irradiated from above, and the term "back" or "behind" in section C refers to the lower side in the figure. The whole is housed in a flat box-shaped glass vacuum container 1. A scintillator layer 2 is formed inside the upper surface of this container 1,
A photocathode 3 is vacuum-deposited on its surface (lower surface in the figure). Reference numeral 4 denotes a grid extending below the photocathode 3 in parallel with the photocathode 3, and by switching, it also serves as a photoelectron accelerating electrode and an electric signal extraction electrode.
5 is a pixel-divided electron multiplication microchannel plate. This channel plate has a thickness of about 1 mm, and one channel has a diameter of 20 μm. A second grid 6 is stretched below the channel plate in parallel with the channel plate 5, and is opposed to the bottom inner surface of the vacuum vessel 1. A transparent electrode layer 7 is formed on the bottom inner surface of the vacuum container 1, and an exotic material layer 8 is formed thereon.

Exo materials are insulating materials such as BeO or CaSO _4. When irradiated with electron beams or When the electrons are irradiated with light, the number of electrons corresponding to the previous irradiation dose is emitted from the excited state (trapped state). (electrons trapped in this level are released by photoexcitation). Since electron emission is possible only in an extremely thin layer within several hundred amps from the surface of the exo material, it is desirable to form the exo material layer 8 in FIG. 1 as thin as possible.

When an X-ray image is accumulated in the exo material layer 8 with the above configuration, the photocathode 3 is grounded as shown in FIG.
High voltage is applied sequentially to the lower surface and grid 6,
The transparent electrode 7 is set at the same potential as the grid 6,
An X-ray image is projected onto the top surface of the vacuum container 1. As mentioned in the section on the effect, X-rays are converted into light in the scintillator layer 2, and this light is converted into photoelectrons at the photocathode 3, and these photoelectrons are attracted by an electric field directed vertically downward from the photocathode to generate photoelectric currents. The rays are launched perpendicularly to the surface, accelerated, multiplied by the channel plate 5, and made incident on the exotic material layer 8, where they accumulate an X-ray image. This process corresponds to the photographing process in X-ray photography, and the illustrated vacuum container 1 corresponds to an X-ray film or a cassette containing the same.

Next, the operation of converting the X-ray image accumulated in the exo material layer as described above into an electric video signal will be described. This corresponds to the development process of an X-ray photograph. As shown in FIG. 3, the transparent electrode 7 is grounded, and a high voltage is applied in this order to the grid 6, the lower surface of the channel plate 5, the upper surface of the channel plate 5, and the grid 4.
Exo material layer 8 is scanned with a laser beam from below by light beam scanning means 12 driven by control circuit 11 . The reason why the transparent electrode 7 is provided is that the exo material is insulating, so when it emits electrons, it becomes positively charged and prevents electron emission. Therefore, graphite is mixed with the exo material to make it conductive. , the electrode 7 is grounded to release the positive charge.

Now, when scanning with a laser beam, the exotic material layer 8
A number of electrons proportional to the density of the accumulated image are emitted from the area irradiated with light, and these electrons are accelerated by the action of an upward electric field perpendicular to the bottom of the vacuum chamber 1, and multiplied by the channel plate 5. The signal is captured by the grid 4, becomes an electrical video signal, and is stored in the image memory 10 via the A/D converter 9. In addition,
It is also possible to use the photocathode 3 as a video signal extraction electrode instead of the grid 4, and the grids 4 and 8 can be omitted by replacing the end face of the channel plate with an electron accelerating electrode.

Effects According to the present invention, the electron conversion efficiency of X-rays is high, and since signal amplification is performed twice by the electron multiplier, high sensitivity and high S/N ratio can be obtained. Furthermore, due to the electron transparency of exo materials, the depth at which they can emit electrons is only a few hundred angstroms, so even if they have the property of accumulating an X-ray image by direct X-ray irradiation,
At a thickness of 100 Å, most of the X-rays pass through and the conversion efficiency into exo-electrons becomes extremely low.However, in this invention, the X-ray image is converted into an electron image and accumulated in the exo-material. By doing so, it is possible to increase the efficiency of image input and to perform signal amplification by electron multiplication both during image storage and when converting the image into a video signal.

Note that the structure of the present invention in which the scintillator layer is omitted projects an optical image onto a photocathode, thereby serving as a means for accumulating the optical image and converting it into a video signal.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional side view of one embodiment of the present invention;
The figure is a diagram showing the wiring during image storage in the same embodiment.
The figure is also a diagram showing connections during video signal conversion.

Claims (1)

[Scope of utility model registration request] In order from the X-ray irradiation side in a flat box-shaped vacuum container,
A scintillator layer, a photocathode in close contact with the same layer, an electron multiplication channel plate, and an exo material are arranged in parallel, and a means for scanning the exo material layer with a light beam is provided. When extracting a video signal, a potential gradient that becomes high potential can be applied from the side of the exo material layer toward the photocathode. An X-ray image pickup device configured to extract a video signal by an electrode disposed between the plate and to operate the light beam scanning means when the video signal is extracted.