JPH0772258A - Radiation detector - Google Patents

Abstract

PURPOSE:To make it possible to perform the low-resolution high-speed reading and the high-resolution reading of a radiation image selectively by one radiation detector. CONSTITUTION:A second transistor 33 is provided so that the transistor 33 may be commonly connected to transistors 31G of four neighboring solid-state photodetector elements Pa, Pb, Pc and Pd each comprising a photodiode 31E and the transistor 31G that is connected to the photodiode 31E. At the time of a high-resolution mode, the transistors 31G are sequentially made ON for each of solid-state photodetector elements Pa, Pb, Pc and Pd, and the individual image signal is obtained. At the time of a low-resolution high-speed mode, all four transistors 31G and the second transistor 33 are turned ON at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector, and more particularly to an improvement of the radiation detector which improves the method of reading out image signals from a large number of solid-state photodetector elements constituting the radiation detector. .

[0002]

2. Description of the Related Art Conventionally, in radiography in various fields such as medical radiography for radiography for medical diagnosis, industrial radiography for nondestructive inspection of substances, etc. A so-called radiographic method combined with a radiographic film is used. According to this method, when radiation such as X-rays transmitted through the subject enters the intensifying screen, the phosphor contained in the intensifying screen absorbs the energy of this radiation and emits fluorescence (instantaneous emission). Due to this light emission, the radiographic films superposed so as to be in close contact with the intensifying screen are exposed to light, and a radiographic image is formed on the radiographic film. In this way, the radiation image can be directly obtained as an image visualized on the radiation film.

On the other hand, in various fields, a radiographic image recorded on a radiographic film is photoelectrically read to obtain an image signal, the image signal is subjected to appropriate image processing, and then the image is reproduced and recorded. It is being appreciated. For example, an X-ray image is recorded using a film having a low gamma value designed so as to be suitable for later image processing, and the X-ray image is read from the film on which the X-ray image is recorded and converted into an electric signal. By performing image processing on this electric signal (image signal) and reproducing it as a visible image on a copy photograph or the like, a reproduced image with good image quality performance such as contrast, sharpness, and graininess is obtained. (See Japanese Patent Publication No. 61-5193).

In addition, the applicant of the present invention has conducted radiation (X-ray, α
Ray, β ray, γ ray, electron beam, ultraviolet ray, etc.), a part of this radiation energy is accumulated, and when excitation light such as visible light is then irradiated, stimulated emission is shown according to the accumulated energy. By using a stimulable phosphor (stimulable phosphor), the radiation image information of a subject such as a human body is once recorded on a sheet-shaped stimulable phosphor, and this stimulable phosphor sheet is excited by a laser beam or the like. Scan to generate stimulated emission light, photoelectrically read the obtained stimulated emission light to obtain an image signal,
A radiation image recording / reproducing system for outputting a radiation image of a subject as a visible image on a recording material such as a photographic light-sensitive material or a CRT based on this image data has already been proposed (JP-A-55-12429, JP-A-56-56). No. 11395, No. 55-163472,
56-104645, 55-116340, etc.).

This system has the practical advantage of being able to record images over a very wide radiation exposure area as compared to conventional radiographic systems using silver halide photography. That is, in the stimulable phosphor, it has been recognized that the amount of emitted light stimulated by excitation after storage is proportional to the radiation exposure dose over a very wide range, and therefore the radiation exposure dose varies depending on various imaging conditions. Even if it fluctuates significantly, the amount of stimulated emission light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means with the reading gain set to an appropriate value and converted into an electric signal. Recording material such as photographic light-sensitive material,
By outputting a radiation image as a visible image on a display device such as a CRT, it is possible to obtain a radiation image that is not affected by variations in radiation exposure dose.

However, in order to obtain a radiographic image with such a radiographic system, when the above-mentioned radiographic image is directly visualized, the radiographic film used for radiography and the intensifying screen are made to coincide in sensitivity region. Need to do.

In the system for photoelectrically reading a radiation image using the above-described radiographic film and stimulable phosphor sheet, image processing is performed on the radiation image to adjust the density and contrast according to the purpose. Or, the radiation image must be converted into an electric signal once, and it is necessary to perform reading scanning using an image reading device for that purpose, which makes the operation for obtaining the radiation image complicated and obtains the radiation image. It takes time to get to.

Therefore, in order to solve the above problems caused by the conventional system, a radiation detector has been proposed (for example, Japanese Patent Laid-Open Nos. 59-211263 and 2-164067).
Publication, PCT International Publication Number WO92 / 06501, Signal, n
oise, and read out considerations in the developmen
t of amorphous silicon photodiode arrays for radio
therapy and diagnostic x-ray imaging, LE Antonuk
et.al, University of Michigan, RAStreet Xerox,
PARC, SPIE Vol.1443 Medical Imaging V; Image Physic
s (1991), p.108-119).

This radiation detector comprises, for example, a plurality of solid-state photodetector elements arranged in a matrix of transparent conductive films and conductive films sandwiching an amorphous semiconductor film on a substrate made of quartz glass having a thickness of 3 mm and orthogonal to each other. As described above, a scintillator for converting radiation into visible light is laminated on a solid-state photodetector composed of a plurality of signal lines and scanning lines which are patterned in a matrix.

By arranging this radiation detector so that the scintillator faces the surface on the radiation incident side, and irradiating the radiation detector with the radiation transmitted through the subject, the radiation is directly incident on the scintillator and converted into visible light. The converted visible light is detected by the photoelectric conversion unit of the solid-state light detection element and photoelectrically converted into an image signal carrying radiation image information. This image signal is read out by a predetermined reading means from a transfer section provided corresponding to each solid-state photodetecting element of the radiation detector and output to the outside.

On the other hand, a radiation detector which does not require a scintillator has also been proposed. This radiation detector has the scintillator removed in the above-mentioned radiation detector, and (i) radiation of The solid-state photodetector (MATE
RIAL PARAMETERS IN THICK HYDROGENATED AMORPHOUS SI
LICON RADIATION DETECTORS, Lawrence Berkeley Labora
tory.University of California, Berkeley.CA 94720 Xe
rox Parc.Palo Alto.CA 94304), or (ii) a solid-state photodetector (Metal / Amorphous Silicon Multilayer Radiat) in which two or more layers are stacked with a metal plate in the radiation transmission direction.
ion Detectors, IEE TRANSACTIONS ONNUCLEAR SCIENCE.V
OL.36.NO.2.APRIL 1989), or (iii) CdTe
A radiation detector having a configuration using a semiconductor radiation detector (Japanese Patent Laid-Open No. 1-216290) such as, for example, directly detecting radiation without passing through visible light and converting it into an electric signal or the like. The signals are read-out signals input to the scanning lines in the same manner as the radiation detectors described above, and the solid-state photodetection elements arranged in a matrix form (a number of elements constituting the radiation detectors (i) to (iii) above). ) Is read and output separately.

The image signal output in this way is subjected to various signal processing by a signal processing device in the subsequent stage, and then CR.
It is reproduced as visible information or the like by a reproducing means such as T.

By using the above radiation detector, the radiation image of the subject can be obtained in real time without complicated operations, and the radiation image information can be immediately reproduced. It can be resolved.

[0014]

By the way, since the radiation detector can obtain a radiation image signal in almost real time as described above, it is possible to detect the radiation image signal of the subject one after another in a cycle of, for example, about 30 Hz and to make it visible. By imaging, the radiation image of the subject can be reproduced as a moving image. In such a high-speed moving image, the resolution of each of the many radiographic images that make up the moving image is
It does not have to be as high in resolution as a still image. Also, even for still images, high resolution is not required,
Even if the resolution is low to some extent, it may not affect the observation and interpretation. In particular, in the case of the moving image described above, it is required that the output speed of the image be higher than the resolution of each image.

The present invention has been made in view of the above circumstances, and in the case of selectively outputting one of a low resolution image signal and a high resolution image signal to output a low resolution image signal, An object of the present invention is to provide a radiation detector that outputs at a higher speed than when a high-resolution image signal is output.

[0016]

A radiation detector according to the present invention sequentially outputs image signals detected by each photoelectric conversion unit from a first transfer unit connected to each photoelectric conversion unit. An image signal capable of reproducing a high-resolution image is output by. On the other hand, the image signals respectively detected by a plurality of adjacent photoelectric conversion units are simultaneously output from the first transfer unit, and the second transfer units commonly connected to the plurality of first transfer units make the first By combining the image signals that have passed through the transfer unit and outputting them from the second transfer unit, the plurality of image signals detected by the plurality of photoelectric conversion units are output as one image signal, and as a result, the plurality of photoelectric conversions are performed. The part can be treated as one large pixel. In this case, an image signal capable of reproducing a low resolution image is output as the entire image. In the latter case, since the image signals from the plurality of photoelectric conversion units are output by one transfer unit (second transfer unit), the switching operation time of the second transfer unit required for output as the entire radiation detector is reduced. The sum total is shorter than the sum of the switching operation times of the first transfer units that individually output image signals from the respective photoelectric conversion units, and therefore the output time of the image signals is shortened.

That is, the first radiation detector of the present invention has a photoelectric conversion unit for detecting radiation carrying image information and converting it into an image signal representing a radiation image as a whole, as described in claim 1. A radiation detector comprising a plurality of solid-state photodetection elements arranged two-dimensionally, the transfer section outputting an image signal stored in the photoelectric conversion section to the outside according to a predetermined scanning signal. A plurality of transfer units that are provided for each of the photoelectric conversion units and that individually output the image signals converted by the photoelectric conversion units and that are provided in a plurality of adjacent photoelectric conversion units. A second transfer unit that is commonly connected to the first transfer unit and outputs a signal output through the plurality of first transfer units; and the first transfer unit and the second transfer unit. To switch the plurality of adjacent photoelectric It is characterized by comprising switching means for selecting a high resolution mode in which the output from the conversion unit is separately output and a low resolution high speed mode in which the signals output through the first transfer unit are output together. It is a thing.

Here, the term "adjacent" means that the two-dimensional array is continuous in at least one of the vertical direction, the horizontal direction, and the oblique direction.

As the radiation detector, for example,
A plurality of solid-state photo-detecting elements arranged in a matrix of a transparent conductive film and a conductive film with an amorphous semiconductor film sandwiched between them and a pattern formed in a matrix so as to be orthogonal to each other on a substrate made of quartz glass having a predetermined thickness. A solid-state photodetector composed of a plurality of signal lines and scanning lines, which has a thickness of 10 times thicker than the normal one in (i) the transmission direction of radiation described above. Vessel, (i
It is possible to use a solid-state photodetector in which i) two or more layers are laminated in the radiation transmission direction via a metal plate, and (iii) a semiconductor radiation detector such as CdTe. Further, it is also possible to use a solid-state photodetector including a solid-state photodetection element such as an ordinary photodiode. In this case, Gd ₂ which is irradiated with radiation and is converted into visible light having an intensity corresponding to the intensity of the radiation
A scintillator made of a fluorescent substance such as O ₂ S or CsI may be laminated on the solid-state photodetector.

The predetermined thickness means a thickness at which the amount of absorbed radiation is not so large as to deteriorate the image quality of a radiation image, but more specifically, to a certain degree for supporting the solid-state photodetector. It is said that it is about several hundreds of microns because the strength of is required.

As the first and second transfer parts, for example, transistors can be used.

[0022]

According to the radiation detector of the present invention, the switching operation of the first transfer section or the second transfer section is selected by the switching means according to the desired resolution, and the high resolution mode is selected. In this case, since the image signals converted by the photoelectric conversion units are sequentially output by the first transfer unit, the output time of the image signal becomes longer as a whole of the radiation detector. Since the image signals having the same resolution as the number are output, a high-resolution image can be reproduced. On the other hand, when the low resolution high speed mode is selected, the image signals respectively detected by the plurality of photoelectric conversion units adjacent to each other are simultaneously output by each first transfer unit, and the plurality of simultaneously output images are output. The signals are combined and output by the second transfer unit. In this case, the plurality of image signals detected by the plurality of photoelectric conversion units connected to one second transfer unit via the first transfer unit are 1
It is output as one image signal, whereby a plurality of photoelectric conversion units can be handled as one large pixel. Therefore, an image signal capable of reproducing a low resolution image is output as the entire image. Further, the image signals from the plurality of photoelectric conversion units are transferred to one transfer unit (second transfer unit).
Therefore, the sum of the switching operation times of the second transfer units required for the radiation detector as a whole to be output is greater than the sum of the switching operation times of the first transfer units that individually output the image signals from the photoelectric conversion units. Therefore, the output time of the image signal is shortened and the output time is shortened.

As described above, according to the radiation detector of the present invention, a low resolution image signal and a high resolution image signal can be selectively output, and when a low resolution image signal is output, a high resolution image signal is output. It is possible to output at a higher speed than when an image signal of resolution is output.

[0024]

Embodiments of the radiation detector according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a radiation detector of the present invention, and FIG. 2 is a system diagram showing an outline of a radiation image information detection system using the radiation detector of this embodiment. . As shown in FIG. 2, the illustrated radiation detector 30 is stacked on the scintillator 32, and a flat scintillator 32 that receives the radiation R emitted from the radiation source 20 and transmitted through the subject 10 and converts it into visible light. A large number of two-dimensional solid-state photodetectors P (Pa, Pb, Pc, P) that detect the visible light converted by each part of the scintillator 32 and convert it into an image signal E representing a radiation image as a whole.
solid-state photodetector 31 in which d) is arranged.

Here, the detailed structure of the solid-state photodetector P is shown in FIG. Each solid-state photodetector P is a signal line made of a conductive film patterned on a substrate 31A made of a resin sheet.
31B and 31H, which are formed by a photodiode 31E composed of an amorphous silicon 31C and a transparent electrode 31D, and a first thin film transistor 31G composed of a transfer electrode 31J as a gate provided in the amorphous silicon 31F and 31F.

Further, as shown in FIG.
X 2 horizontal (4 in total) solid-state photodetectors Pa, Pb,
A first thin film transistor (hereinafter simply referred to as the first transistor) 31G connected to Pc and Pd, respectively
In addition, as shown in FIG. 1B, a second thin film transistor (hereinafter, simply referred to as a second transistor) 33 commonly connected is provided over the entire surface of the solid-state photodetector 31.

Further, a switching means 34 for generating a switching signal for controlling opening / closing of the first transistor 31G and the second transistor 33, a scanning pulse generator 35 for generating a scanning pulse according to the switching signal, 1 transistor 31
A transfer register 36 to which the image signal converted by each photodiode 31E is transferred and output via G and the second transistor 33.

Next, the operation of the radiation detector 30 of this embodiment will be described.

As shown in FIG. 2, the radiation detector 30 is provided with an object.
The radiation R is irradiated via 10 and the radiation detector 30 which has been irradiated with the radiation R converts this radiation R into visible light according to its intensity by the scintillator 32. Therefore, this visible light carries the radiation image information of the subject 10 and is received by the photodiode 31E of each solid-state light detecting element P, and a signal charge according to this image information is generated in the photodiode 31E. In this way, a signal charge proportional to the intensity of the radiation R incident on each solid-state photodetector P is generated.

When it is desired to output an image signal for reproducing a high-resolution image, a signal indicating high resolution is input to the switching means 34 by an input means (not shown), and the switching means 34 responds to the input signal. A high resolution mode signal is generated, and this high resolution mode signal is input to the scanning pulse generator 35. The scanning pulse generator 35 simultaneously turns on the transistor 31G provided in the solid-state photodetector Pa and the second transistor 33 according to the input mode signal (voltage is applied to the transfer electrode 31J in FIG. 3, and the signal line 31B / Current between 31H) and other solid-state photodetector Pb,
The first transistor 31G provided in Pc and Pd is turned off.
Keep in F state. As a result, the image signal stored in the solid-state photodetector Pa is sent to the transfer register 36. Then, the first transistor 31G and the second transistor 33 of the solid-state photodetector Pb are simultaneously turned on, and the other three first transistors 31G are turned off, and the solid-state photodetector Pb is charged. Image signal transfer register 36
Send to.

The above operation is performed by using the other solid-state photodetectors Pc, P
By sequentially repeating for d, image signals are sequentially stored in the transfer register 36 from the solid-state photodetectors Pa, Pb, Pc, and Pd, respectively, and the image reproduction means (not shown)
It is possible to obtain a high-resolution image by reading out these image signals from the transfer register 36 in time series and reproducing the radiation image based on these image signals.

On the other hand, when it is desired to output an image signal showing a low resolution image at high speed, a signal showing a low resolution is input to the switching means, and the switching means 34 outputs a low resolution mode signal corresponding to the input signal. Is generated and this mode signal is input to the scanning pulse generator 35. The scanning pulse generator 35 receives the solid-state photodetectors Pa, Pb, Pc, Pd according to the input mode signal.
Each first transistor 31G and second transistor of
33 is turned on at the same time. By this operation, the image signals stored in the solid-state photodetectors Pa, Pb, Pc, and Pd pass through the first transistors 31G, respectively, and are added by the second transistor 33 to form one image signal. It is input to the transfer register 36. The image signal stored in the transfer register 36 includes four solid-state photodetectors Pa, Pb,
Since there is one for each of Pc and Pd, the radiation image reproduced based on this image signal is an image having a resolution of 1/4 of the high resolution. However, the four first transistors 31
Since the G and the second transistor 33 are opened and closed only once, the operation time required for this is about 1/4 of that in the high resolution mode, and the output time of the image signal can be shortened.

As described above, according to the radiation detector of this embodiment, one radiation detector selectively obtains one of an image signal representing a low-resolution image and an image signal representing a high-resolution image. In addition, when outputting a low-resolution image signal, the speed can be increased as compared to when outputting a high-resolution image signal.

In the radiation detector of the present invention, in the low-resolution high-speed mode, the number of the vertical m × horizontal n solid-state photodetectors is 1.
The second transistor may be connected so as to be treated as one pixel, and in addition to the one in which two vertical × two horizontal solid-state photodetectors are treated as one pixel as in the above embodiment, FIG.
As shown in (4), by connecting four vertical × one horizontal solid-state photodetectors by one second transistor 33, it is possible to adopt a configuration in which they are handled as one pixel.

As the solid-state photodetector of this embodiment, for example, (i) the solid-state photodetector in which the heat in the radiation transmitting direction is set to be about 10 times thicker than the normal one, or (ii) the radiation transmitting In the direction, a solid-state photodetector in which two or more layers are stacked via a metal plate, (iii) a semiconductor radiation detector such as CdTe, etc. can be used. Etc., and the radiation detector in this case can have a configuration without a scintillator that converts radiation into visible light.

[Brief description of drawings]

FIG. 1A is a block diagram showing a configuration of an embodiment of a radiation detector of the present invention. FIG. 1B is a block diagram showing a part of the radiation detector shown in FIG. 1A.

FIG. 2 is a system diagram showing a radiation image information detection system using the radiation detector shown in FIG.

FIG. 3 is a diagram showing a detailed structure of a solid-state photodetector.

FIG. 4 is a diagram showing another embodiment of the radiation detector of the present invention.

[Explanation of symbols]

 10 subject 20 radiation source 30 radiation detector 31 solid-state photodetector 31E photodiode 31G first transistor 32 scintillator 33 second transistor 34 switching means 35 scanning pulse generator 36 transfer register P, Pa, Pb, Pc, Pd solid state Photo detector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 27/14 H04N 5/32

Claims (1)

[Claims] 1. A photoelectric conversion unit for detecting radiation carrying image information and converting it into an image signal representing a radiation image as a whole, and an image signal stored in the photoelectric conversion unit according to a predetermined scanning signal. A radiation detector in which a plurality of solid-state photodetection elements, each of which is composed of a transfer section for outputting the photoelectric conversion section to the outside, are arranged in a two-dimensional manner, wherein the transfer section is provided for each photoelectric conversion section. First outputting the image signals converted by the unit separately
And a second transfer unit that is commonly connected to the plurality of first transfer units provided in the plurality of adjacent photoelectric conversion units and that outputs a signal output through the plurality of first transfer units. A mode in which a transfer unit, the first transfer unit and the second transfer unit are switched, and outputs from the plurality of adjacent photoelectric conversion units are separately output, and a signal output through the first transfer unit. And a switching means for selecting a mode for outputting the combined radiation.