JPH0772253A - Method for reading radiation image signal and radiation detector used therefor - Google Patents

Abstract

PURPOSE:To make it possible to form a radiation image having the uniform S/N over the entire image by reading out the image signal from a solid-state photodetector element nonlinearly over a plurality of lines of matrix. CONSTITUTION:Radiation R from a radiation source 20 is transmitted through an object 10 and applied on a detector 30. The radiation R is converted into the visible light through a scintillator 33. The light is received by each of facing solid-state photodetector elements 31 for every part of the scintillator 33, and the signal electric charge is generated. Then, a transfer pulse is sent into a scanning line 32M from a scanning-pulse generator 35. At this time, the scanning pulse is sent into the odd-numbered line of the scanning lines 32M, which are nonlinearly provided in the line direction of the matrix. Thus, the image signals are read out of the half of the elements 31. Then, the scanning pulse is sent into the even-numbered scanning line 32M and the signals are read out of the remaining elements 31. Therefore, the elements having the time differences required from the start of the reading to the end are evenly distributed as the entire solid-state photodetector 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reading out a radiation image and a radiation detector used in the method, and more particularly to improving the order of reading out image signals from a large number of solid-state photodetector elements constituting the radiation detector. It is about.

[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 is composed of a plurality of solid-state photodetectors 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 that converts radiation into visible light is stacked on a solid-state photodetector that is composed of a plurality of signal lines and scanning lines that 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 and output from a transfer unit provided in each solid-state light detecting element of the radiation detector by a predetermined reading means.

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 signal is a solid-state photodetector arranged in a matrix in accordance with a read signal input to the scanning line similarly to the above-mentioned radiation detector (a large number of elements constituting the radiation detector of (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]

In the above radiation detector, the scanning lines are linearly connected to each row of the solid-state photodetection elements arranged in a matrix, and the signal lines are linearly connected to each column. The read signal is sent to the scanning line connected to the solid-state photodetection elements in the uppermost row of the matrix by the read-out means, and the read-out signal causes the image signal stored in each solid-state photodetection element in the uppermost row to be transmitted. , Is sent to the signal line connected to each of the solid-state photodetectors and stored in the register connected to the signal line. In this way, the read signal is sequentially sent from the scanning line in the uppermost row to the scanning line in the lowermost row, and the image signal stored in each solid-state photodetecting element is read out.

Therefore, there is a time lag between when the reading of the image signal is started from the solid-state photodetecting element in the uppermost row and when the reading of the image signal is finished from the solid-state photodetecting element in the lowermost row. Become.

By the way, the solid-state photodetector element has a drawback that a noise component due to a so-called dark current is stored until the signal is read out even after the irradiation of the radiation is completed. Since the signals were sequentially read from the solid-state photodetector elements in the row, the dark current noise value included in the image signal obtained from the solid-state photodetector elements in the top row and the solid-state photodetection in the bottom row were detected due to the above-mentioned read time difference. There is a difference from the value of the dark current noise of the image signal obtained from the element, and the image reproduced by it has a S / N ratio as a whole.
Will be non-uniform.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a radiation image signal reading method for obtaining a radiation image having a uniform S / N over the entire image and a radiation detector used therefor. It is what

[0018]

According to the radiation image signal reading method of the present invention, a radiation detector having a large number of solid-state photodetection elements arranged in a matrix is used to nonlinearly extend over a plurality of rows of the matrix. The image signal is read out from the solid-state photodetector over the entire radiation detector so as not to overlap.

That is, according to the radiation image signal reading method of the present invention, as described in claim 1, the radiation carrying the image information is detected and converted into an image signal representing a radiation image as a whole and arranged in a matrix. In a radiation image signal reading method for reading the image signal from a radiation detector composed of a large number of solid-state photodetection elements, a plurality of rows are arranged from one end column to the other end column of the matrix. By linearly reading the image signal from the solid-state photodetector, shifting the starting point of the read-out, and repeating the above-mentioned read out so as not to overlap with the already-read solid-state photodetector, the entire radiation detector is covered. It is characterized in that it is read out by reading.

Further, the radiation detector of the present invention is a radiation detector used in the above-mentioned radiation image signal reading method, and as described in claim 2, radiation radiation carrying image information is detected to obtain a radiation image as a whole. A plurality of solid-state photodetector elements arranged in a matrix for storing the converted image signals, and a plurality of non-linearly extending from one end row of the matrix to the other end row across a plurality of rows. A plurality of scanning lines for connecting the solid-state photodetection elements, connecting all the solid-state photodetection elements without overlapping as a whole, transmitting a scanning signal for outputting an image signal from each of the solid-state photodetection elements, and the matrix A signal line for transmitting the image signal detected by the solid-state photodetector to the outside, which is connected to the solid-state photodetector in each column for each column. That.

As the radiation detector, for example,
A plurality of solid-state photodetector elements arranged in a matrix formed of a transparent conductive film and a conductive film with an amorphous semiconductor film interposed therebetween and a pattern formed in a matrix pattern 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. Bowl, (ii)
A solid-state photodetector in which two or more layers are stacked via a metal plate in the radiation transmission direction, or a semiconductor radiation detector such as (iii) CdTe can be used. Furthermore, a solid-state photodetector including a solid-state photodetection element such as an ordinary photodiode can also be used. In this case, Gd ₂ O that receives irradiation of radiation and converts it into visible light having an intensity corresponding to the intensity of the radiation
It is also possible to employ a structure in which a scintillator made of a phosphor such as ₂ S or CsI is laminated on a 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.

[0023]

According to the radiation image signal reading method of the present invention, a radiation detector having a large number of solid-state photo-detecting elements arranged in a matrix form a non-linear manner across a plurality of rows of the matrix. Since the image signal is read out over the entire radiation detector by repeating the reading out of the image signal, unlike the conventional method of sequentially reading out the image signal from the top row, there is a time lag between the beginning of reading and the end of reading. Becomes discretely distributed over the entire matrix, and the image reproduced thereby has a uniform S / N as a whole.

[0024]

1 is a plan view showing an embodiment of a radiation detector used in a radiation image signal reading method of the present invention, FIG.
FIG. 3 is a configuration diagram showing a detailed configuration of a solid-state photodetector 32 that constitutes the radiation detector of this embodiment. Further, FIG. 3 is an arrangement diagram showing an arrangement of radiation detectors for detecting a radiation image of a subject by this radiation detector. Illustrated radiation detector 30
Is a flat scintillator 33 that converts the incident radiation R that has passed through the subject 10 into an intensity that corresponds to its intensity, and the visible light emitted from each part of the scintillator 33 to detect the entire And a solid-state photodetector 32 formed by arranging a plurality of solid-state photodetectors 31 for photoelectrically converting into an image signal showing a radiation image in a matrix. Here, the scintillator 33 is a phosphor made of Gd ₂ O ₂ S, CsI, or the like. Further, each solid-state light detection element 31 includes a photoelectric conversion unit 38 that photoelectrically converts visible light, and a transfer unit 34 that accumulates the image signal photoelectrically converted by the photoelectric conversion unit 38 and reads it according to a predetermined read signal. From one end row of the matrix to the other end row (see FIG. 1).
In the left-right direction) are connected by a plurality of scanning lines 32M that extend non-linearly across two rows and a plurality of signal lines 32N that extend in each column of the matrix.
Is connected to the scanning pulse generator 35 and the transfer unit 34 of each solid-state photodetector 31. On the other hand, the signal line 32N is a transfer register
36 and the transfer unit 34.

Here, the details of the solid-state photodetector 31 will be described. As shown in FIG. 1, the solid-state photodetector 31 has signal lines 31B and 31H made of a patterned conductive film on a substrate 31A made of a resin sheet.
A photodiode 31E as a photoelectric conversion part 38 composed of 31C and a transparent electrode 31D, and a thin film transistor 31G as a transfer part 34 having a transfer electrode 31J in an amorphous silicon 31F. Here, the transfer electrode 31J is a gate and is connected to the scanning line 32M,
The signal line 31H is a drain and is connected to the above-mentioned signal line 32N. A solid-state photodetector is obtained by arranging a plurality of solid-state photodetectors 31 having such a configuration in a two-dimensional manner.
32 are configured.

FIG. 4 is a diagram schematically showing a wiring state of the scanning lines 32M with respect to the solid-state photodetecting elements 31 arranged in a matrix. As described above, the scanning lines 32M (in order from the scanning line in the uppermost row, 32M ₁ , 32M ₂ , ...) are not linear in the row direction of the matrix, and are alternated over two rows, one solid light in each column. It is connected to the detection element 31.

Next, the operation of the radiation detector 30 of this embodiment will be described. As shown in FIG. 3, the radiation R emitted from the radiation source 20 is applied to the subject 10 and passes through the subject 10. The radiation R transmitted through the subject 10 is applied to the radiation detector 30. The radiation R applied to the radiation detector 30 is
The scintillator 33 converts the incident radiation into visible light that emits light with an intensity corresponding to the intensity. The visible light after the conversion is received by the photodiode 31E of each solid-state photodetecting element 31 facing each part of the scintillator 33, and a signal charge is generated in the photodiode 31E.

[0028] Then the scanning pulse generator 35, firstly transfer pulse to the scan line 32M ₁ are transmitted, is connected to the scanning line 32M _1, each solid-state photodetection elements attached diagonal lines in FIG. 4 31
Indicates that the switch is in the “ON” state (a voltage is applied to the transfer electrode 31J of the solid-state photodetection element 31, and a current flows between the signal lines 31B / 31H). That is, the signal charge generated in the photodiode 31E is transferred through the thin film transistor 31G. As a result, the signal charges stored in the solid-state photodetector elements 31 hatched in FIG.
It is simultaneously sent to the transfer register 36 through 32N. From the output terminal 37 of the transfer register 36, the signal stored for each solid-state photodetection element 31 is taken out in time series.

Next, the scanning line 32M ₃ from the scanning pulse generator 35.
A transfer pulse is sent to the
An image signal is output from the solid-state photodetector 31 connected to 32M ₃ .

This operation is sequentially performed on the scanning lines 32M ₅ and 32M ₇ , and then the scanning lines 32M ₂ , 32M ₄ and 32.
The same action is sequentially performed on M ₆ and 32 M ₈ .

By sending the scan pulse to the odd-numbered scan lines 32M ₁ , 32M ₃ , ... Of the scan lines 32M ₁ , 32M ₂ ,. Image signals are read from the half of the solid-state photodetectors 31 distributed over the entire surface of the solid-state photodetector 32, and then scan pulses are sent to the even-numbered scan lines 32M ₂ , 32M ₄ ,. Since the image signal is read from the detection element 31, the solid-state photodetection elements 31 having a time difference required from the start of reading the image signal to the completion of the reading are uniformly distributed as the whole of the solid-state photodetector 32, and each of the solid-state photodetectors during this time difference The noise signal due to the dark current stored in the solid-state photodetector 31 will also be distributed evenly over the entire solid-state photodetector 32.

As described above, according to the radiation detector of this embodiment, the radiation image reproduced by the detected image signal can have a uniform S / N over the entire image.

When reproducing an image that does not require high resolution, such as when the reproduced radiation image is used as a moving image, in the radiation detector of this embodiment, the odd-numbered scanning line 32M _{1 is used.} , 32M ₃ , ..., using only the image signal obtained by sending the scan pulse, or using only the image signal obtained by sending the scan pulse to the even-numbered scan lines 32M ₂ , 32M ₄ ,. Image can be reproduced, and in this case, the reading speed of the image signal can be improved.

The radiation detector according to the present invention is not limited to the embodiment described above. For example, the scanning lines 32M ₁ , 32M ₂ , ... As shown in FIG. It is also possible to adopt an aspect in which the solid-state photodetection elements 31 in each row of the matrix of the detection elements 31 are alternately connected to each row.

In the solid-state photodetector 32 shown in FIG. 5, a transfer pulse is sent to the scanning line 32M ₃ connected to the solid-state photodetecting element 31 in the first row of the leftmost column of the matrix, and this scanning line is sent.
Image signals are read out from a plurality of solid-state photodetector elements 31 connected to 32M ₃ , and then the solid-state photodetector elements in the fifth row are read.
31 transfer pulse to the scanning lines 32M ₇ connected is sent to the image signal is read out from the plurality of solid state light detection element 31 connected to the scanning line 32M _7.

Next, the transfer pulse is sequentially sent to the scanning lines 32M ₄ and 32M ₈ to perform the same operation as described above, and then the transfer pulse is sent to the successive scanning lines 32M ₁ , 32M ₅ , 32M ₂ and 32M _6. To be Each solid-state photodetector connected to each scanning line
Image signals are read from 31 in the order in which each transfer pulse is sent.

As described above, according to the radiation detector of this embodiment, since the image signal is discretely read over the entire surface of the radiation detector, the radiation image reproduced based on the read image signal is The dark current noise is averaged and the S / N is averaged for the entire image.

The radiation detector according to the present invention is not necessarily limited to the one using the scintillator as in the above-mentioned embodiment, but in the radiation detector of the above-mentioned embodiment, instead of the solid-state photodetector, for example, the above-mentioned (I) The solid-state photodetector whose thickness in the radiation transmission direction is set to be about 10 times thicker than the normal one, or (ii) in the radiation transmission direction,
If two or more solid-state photodetectors stacked with a metal plate interposed therebetween or (iii) a semiconductor radiation detector such as CdTe are used, there is no need to provide a scintillator.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a radiation detector used in a radiation image reading method of the present invention.

FIG. 2 is a configuration diagram showing a detailed configuration of a solid-state photodetector that constitutes the radiation detector of this embodiment.

FIG. 3 is a layout diagram showing a layout of radiation detectors that detect a radiation image of a subject.

FIG. 4 is a schematic diagram schematically showing a wiring state of scanning lines of a radiation detector.

FIG. 5 is a schematic diagram showing a wiring state of scanning lines according to another embodiment.

[Explanation of symbols]

 10 Subject 20 Radiation source 30 Radiation detector 31 Solid-state photodetector 31A Substrate 31B, 31H Signal line 31C, 31F Amorphous silicon 31D Transparent electrode 31E Photodiode 31G Thin film transistor 31J Transfer electrode 32 Solid-state photodetector 32M Scan line 32N Signal line 33 Scintillator 34 Transfer unit 35 Scanning pulse generator 36 Transfer register 37 Output terminal 38 Photoelectric conversion unit

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

Claims (2)

[Claims] 1. A radiation detector comprising a large number of solid-state photodetection elements arranged in a matrix for detecting radiation carrying image information, converting it into an image signal representing a radiation image as a whole, and accumulating the image signal. In a radiation image signal reading method for reading a signal, an image signal is non-linearly read from a solid-state photodetector over a plurality of rows from one end column to the other end column of the matrix, and the starting point of the reading is performed. The radiation image signal reading method is characterized in that the reading is repeated over the entire radiation detector by repeating the reading so as not to overlap with the already read solid-state light detecting element. 2. A large number of solid-state photodetection elements arranged in a matrix for detecting radiation carrying image information, converting it into an image signal representing a radiation image as a whole, and accumulating it.
A plurality of solid-state photodetection elements are connected non-linearly across a plurality of rows from one end column of the matrix to the other end column, and all solid-state photodetection elements are connected without overlapping as a whole. A plurality of scanning lines transmitting a scanning signal for outputting an image signal from each of the solid-state photodetectors, and the solid-state photodetectors connected to each of the solid-state photodetectors of each column of the matrix, A radiation detector, comprising: a signal line for transmitting the detected image signal to the outside.