JP3717530B2 - Radiation image detector - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a radiation image detector, and more particularly to a radiation image detector that utilizes a combination of a scintillator and a solid state detector.
[0002]
[Prior art]
Conventionally, intensifying screens and radiographic films have been used for radiography in various fields such as medical radiography for radiography for medical diagnosis and industrial radiography for destructive inspection of substances. A combination so-called radiography method 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 the radiation and emits fluorescence (instant light emission). By this light emission, the radiographic film superimposed so as to be in close contact with the intensifying screen is exposed, and a radiographic image is formed on the radiographic film. In this way, the radiation image can be obtained directly as an image visualized on the radiation film.
[0003]
On the other hand, a radiographic image recorded on a radiographic film is photoelectrically read to obtain an image signal, and after appropriate image processing is performed on the image signal, the image is reproduced and recorded in various fields. . For example, an X-ray image is recorded using a film having a low gamma value designed 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. The electrical signal (image signal) is subjected to image processing and then reproduced as a visible image on a copy photograph or the like to obtain a reproduced image with good image quality performance such as contrast, sharpness, and graininess. (See Japanese Patent Publication No. 61-5193).
[0004]
In addition, when the applicant of the present invention irradiates radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of the radiation energy is accumulated, and when irradiated with excitation light such as visible light thereafter Using a stimulable phosphor (stimulable phosphor) that exhibits stimulating luminescence in response to the generated energy, radiation image information of a subject such as a human body is temporarily recorded on the sheet-like stimulable phosphor, and this accumulation is performed. The photosensitive phosphor sheet is scanned with excitation light such as laser light to generate stimulated emission light, and the resulting stimulated emission light is photoelectrically read to obtain an image signal. Based on this image data, a radiographic image of the subject Image recording / reproducing system that outputs a visible image on a recording material such as a photographic photosensitive material or a CRT has already been proposed (Japanese Patent Laid-Open Nos. 55-12429, 56-11395, 55-163472, 56-104645 and 55-116340).
[0005]
This system has a practical advantage that an image can be recorded over a very wide radiation exposure range as compared with a conventional radiographic system using silver salt photography. That is, in the stimulable phosphor, it is recognized that the amount of emitted light that is stimulated and emitted by excitation after accumulation is proportional to the radiation exposure amount over a very wide range. Therefore, the radiation exposure amount varies depending on various imaging conditions. However, the amount of stimulated emission light emitted from the stimulable phosphor sheet is set to an appropriate value for the reading gain, read by the photoelectric conversion means, and converted into an electrical signal. Is used to output a radiation image as a visible image on a recording material such as a photographic photosensitive material or a display device such as a CRT, thereby obtaining a radiation image that is not affected by variations in radiation exposure.
[0006]
However, in order to obtain a radiographic image by such a radiographic system, it is necessary to perform imaging by matching the sensitivity areas of the radiographic film used for imaging and the intensifying sheet when directly visualizing the above-described radiographic image. There is.
[0007]
Further, in the system for photoelectrically reading a radiation image using the above-described radiographic film and the stimulable phosphor sheet, the radiation image is subjected to image processing as described above so as to have a density and contrast according to the purpose. It is necessary to adjust or convert the radiographic image into an electrical signal once, and it is necessary to perform a scanning scan using an image reading apparatus for that, and the operation for obtaining the radiographic image becomes complicated, and the radiographic image is It takes time to get it.
[0008]
Therefore, in order to solve the above-mentioned problems caused by the radiographic system, radiation detectors have been proposed (for example, Japanese Patent Laid-Open Nos. 59-211263, 2-164067, PCT International Publication No. WO92). / 06501, Signal, noise, and read out considerations in the development of amorphous silicon photodiode arrays for radiotherapy and diagnostic x-ray imaging, LEAntonuk et.al, University of Michigan, RAStreet Xerox, PARC, SPIE Vol.1443 Medical Imaging V ; Image Physics (1991), p.108-119).
[0009]
This radiation detector has a pattern on a matrix such that a plurality of signal lines and scanning lines made of a transparent conductive film and a conductive film are orthogonal to each other with an amorphous semiconductor film sandwiched between a substrate made of quartz glass having a thickness of 3 mm, for example. It is configured by stacking a scintillator that converts radiation into visible light on a solid detector that is formed and configured.
[0010]
This radiation detector is placed so that the scintillator faces the radiation incident side, and by irradiating the radiation detector with radiation that has passed through the subject, the radiation is directly incident on the scintillator and converted into visible light. The visible light thus detected is detected by a solid state detector and photoelectrically converted into an image signal carrying radiation image information. This image signal is reproduced by a reproducing means such as a CRT after predetermined image processing. By using such a radiation detector, it is possible to immediately reproduce a radiographic image of a subject without complicated operations, and to immediately obtain a radiographic image in real time, eliminating the above-mentioned drawbacks of the radiographic system. can do.
[0011]
[Problems to be solved by the invention]
However, the scintillator used in the radiation detector described above has a large amount of light emission because the radiation is absorbed more in the direction closer to the radiation incident surface in the thickness direction. Therefore, in the above-described radiation detector, the solid state detector is arranged behind the scintillator with respect to the incident direction of radiation, so that the visible light converted by the scintillator reaches the solid state detector before reaching the solid state detector. Absorption by itself, or irregular reflection by the scintillator, the detection efficiency of visible light in the solid state detector is lowered, and the sharpness of the obtained radiographic image is lowered.
[0012]
In view of the above circumstances, an object of the present invention is to provide a radiation image detector capable of improving the detection efficiency of visible light in a solid state detector and improving the image quality of the obtained radiation image .
[0013]
[Means for Solving the Problems]
The radiation image detector according to the present invention converts two irradiated scintillators that convert irradiated radiation into visible light, and converts visible light converted between the two scintillators into electric signals. And a solid state detector.
[0014]
In the radiological image detector according to the present invention, the solid state detector is arranged such that two substrates each having a large number of solid state detection elements are stacked so as to face each other. Two electric signals may be output from the solid-state detection element.
[0015]
Further, in the radiological image detector according to the present invention, the solid state detector is formed such that a large number of solid state detection elements are formed on both sides of a single substrate and two electrical signals are output from the solid state detection elements on both sides. Also good.
[0016]
In this case, a low energy component absorption layer that absorbs a low energy component of the radiation may be provided on the substrate. Further, a low energy component absorbing material that absorbs a low energy component of the radiation may be mixed in the substrate.
[0017]
Furthermore, it is preferable that the radiological image detector according to the present invention further includes a calculation means for calculating the two electric signals.
[0018]
In this case, the calculation means is preferably means for adding the two electric signals, and further preferably means for changing a weight of addition of the two electric signals to be added.
[0019]
Moreover, it is preferable that the said calculating means is a means to perform an energy subtraction process based on the said two electric signals.
[0020]
Furthermore, in the radiographic image detector according to the present invention, the solid state detector may be capable of detecting the visible light from both sides.
[0021]
In the radiological image detector according to the present invention, the thickness of the scintillator on the side irradiated with the radiation is greater than the thickness of the scintillator on the side opposite to the side irradiated with the radiation. It may be thin.
[0022]
Furthermore, in the radiographic image detector according to the present invention, a light reflecting layer for reflecting the visible light may be provided on the outer surface of the two scintillators with the solid state detector interposed therebetween.
[0023]
Moreover, in the radiographic image detector by this invention mentioned above, it is preferable that the said board | substrate shall consist of a substance with little absorption of a radiation like a resin sheet.
[0024]
[Action]
Since the radiation image detector according to the present invention has a configuration in which the above-described solid state detector is disposed between two scintillators, the radiation irradiated to the radiation image detector is the first to be disposed on the radiation irradiation side. Are converted into visible light by a scintillator, and detected by a solid state detector. On the other hand, the radiation that has not been converted to visible light by the first scintillator passes through the solid state detector and reaches the other scintillator after being arranged on the opposite side of the two scintillators where the radiation is irradiated. However, it is converted into visible light by this other scintillator. The visible light converted by this scintillator is detected by the solid state detector together with the visible light converted by the first scintillator. Therefore, the detection efficiency of visible light in the solid state detector is improved, the sharpness of the radiographic image obtained by the radiographic image detector according to the present invention can be improved, and a high-quality radiographic image as a whole can be obtained.
[0025]
In addition, the solid state detector is arranged so that two substrates on which a large number of solid state detection elements are formed are stacked so as to face each other, the solid state detection elements are formed on both sides of one substrate, or visible light is visible from both sides. The visible light converted by each scintillator is detected by the solid-state detection element, and the visible light can be detected more efficiently.
[0026]
In addition, when adding two electrical signals output from each solid state detector, by providing means for changing the weight of the addition, the image quality of the obtained radiographic image can be changed. For example, a high sharpness image can be obtained by heavily weighting the electrical signal obtained by the solid detection element on the radiation incident side, and can be obtained from the solid detection elements on both sides of the solid detector. A highly sensitive radiation image can be obtained by weighting the electrical signal substantially equally.
[0027]
Furthermore, by providing a low energy component absorption layer that absorbs low energy components of radiation on the substrate, or by mixing a low energy component absorbing material that absorbs low energy components, the solid state detection element on the side irradiated with radiation The low energy component of the radiation is detected, and the high energy component from which the low energy component of the radiation is removed is detected on the solid detection element on the opposite side. An energy subtraction image can be obtained by subtracting the electric signals carrying these components with a predetermined weight.
[0028]
Further, by making the thickness of the scintillator on the side irradiated with radiation out of the two scintillators thinner than the thickness of the scintillator on the side not irradiated with radiation, more radiation can be applied to the side irradiated with radiation. Reaches the opposite scintillator, and the visible light converted by the scintillator on the radiation side will not be blurred by the scintillator itself until it reaches the solid state detector. Detection efficiency can be improved.
[0029]
Furthermore, by providing a light reflecting layer that reflects visible light on the outer surface of the two scintillators, the visible light diffusely reflected in the scintillator is reflected toward the solid detector by this reflecting layer. The detection efficiency of visible light in the instrument can be improved.
[0030]
Furthermore, the attenuation | damping of the radiation which permeate | transmits a solid detector can be decreased more by comprising a board | substrate with a substance with little radiation absorption like a resin sheet.
[0031]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0032]
FIG. 1 is a diagram showing a first embodiment of a radiation image detector according to the present invention. As shown in FIG. 1, the radiation image detector 1 according to the first embodiment of the present invention is formed by laminating a solid state detector 2 between two scintillators 3A and 3B. Here, as shown in FIG. 2, the solid state detector 2 has signal lines 12A and 12B made of conductive films patterned on two substrates 11A and 11B made of resin sheets, and amorphous silicon 13A and 13B and A large number of solid state detection elements 18A and 18B are formed by photodiodes 15A and 15B composed of transparent electrodes 14A and 14B and thin film transistors 17A and 17B composed of amorphous silicon 16A and 16B. Further, scintillators 3A and 3B made of a phosphor such as Gd ₂ O ₂ S and CsI are laminated thereon. Here, the scintillators 3A and 3B have a thickness of about several tens of microns to several hundreds of microns. The thickness of the resin sheets 11A and 11B of the solid state detector 2 is about several hundred microns, and the X-ray absorption rate is low. The thickness of the amorphous silicon 13A, 13B is about 1 micron.
[0033]
X-rays 5 emitted from the X-ray source 4 are applied to the subject 6 and pass through the subject 6. X-rays 5 that have passed through the subject 6 are irradiated to the radiation image detector 1. The X-ray 5 irradiated to the radiation image detector 1 reaches the scintillator 3A. The scintillator 3A emits visible light having an intensity corresponding to the intensity of the X-ray 5 that has reached, and this visible light is detected by the amorphous silicon 13A of each solid state detection element 18A. The visible light is photoelectrically converted and electric charges are accumulated in the amorphous silicon 13A in accordance with the emission intensity. Thereafter, this electric charge is read out, and an image signal SA as an electric signal is output.
[0034]
On the other hand, the X-ray 5 that has not been converted into visible light by the scintillator 3A passes through the solid state detector 2 and reaches the scintillator 3B. The scintillator 3B emits visible light having an intensity corresponding to the intensity of the X-ray 5 that has reached, and this visible light is detected by the amorphous silicon 13B of each solid-state detection element 18B. This visible light is photoelectrically converted, and charges are accumulated in the amorphous silicon 13B according to the emission intensity. Thereafter, this electric charge is read out, and an image signal SB as an electric signal is output.
[0035]
When the X-ray 5 passes through the solid state detector 2, the X-ray absorption rate of the substrates 11A and 11B made of a resin sheet is low, and the thickness of the amorphous silicon 13A and 13B is about 1 micron. The X-ray 5 reaches the solid state detector 2 with almost no attenuation.
[0036]
The output image signals SA and SB are input to the information processing means 7 and superimposed at a predetermined ratio, and further subjected to image processing and the like, and the processed image signal S ′ having been processed is input to the reproduction means 8. A radiographic image of the subject 6 is reproduced as a visible image.
[0037]
Here, an image with high sharpness can be obtained by adding a large weight to the image signal SA, and an image with high sensitivity can be obtained by weighting the image signals SA and SB substantially equally. it can.
[0038]
As the reproduction means 8, various devices such as an electronic display such as a CRT, a recording of a radiation image displayed on the CRT or the like on a video printer or the like can be adopted. The radiographic image of the subject 6 may be recorded and stored on a magnetic tape, an optical disk, or the like.
[0039]
In the embodiment described above, the solid state detector 2 is configured by forming a large number of solid state detection elements 18A and 18B on the two substrates 11A and 11B, respectively. For example, as shown in FIG. The solid state detector 2 may be configured by forming a large number of solid state detectors 18A and 18B on both surfaces of a single substrate 11C.
[0040]
In the embodiment described above, a copper plate 19 as a low energy component absorption layer that absorbs a low energy component of X-rays may be disposed between the two substrates 11A and 11B. By arranging the copper plate 19 in this manner, the image signal SA output from the solid-state detection element 18A has a low energy component of X-rays, and the image signal SB output from the solid-state detection element 18B has high energy of X-rays. Each component is carried, and an energy subtraction image can be obtained by performing weighted subtraction on each of the image signals SA and SB. At this time, alignment of each image signal is not necessary, and a good energy subtraction image without positional deviation can be obtained. The low energy component absorption layer is not limited to the copper plate, and any layer may be used as long as it can absorb the low energy component of X-rays. Further, a substance that absorbs low energy components of X-rays may be mixed into the substrates 11A, 11B, and 11C shown in FIGS.
[0041]
Further, in the above-described embodiment, as shown in FIG. 5, a solid detection element 18C may be formed on a single substrate 11D, and the amorphous silicon 13A may be sandwiched between two transparent electrodes 14A and 14C. . Thus, by sandwiching the amorphous silicon between the two transparent electrodes 14A and 14B, it is possible to detect light incident from the direction of arrow A in FIG. 5 and add the image signals of the second embodiment described above. This is more preferable because it is not necessary to perform the treatment.
[0042]
In the embodiment described above, the scintillator 3A on the side irradiated with X-rays may be made thinner than the scintillator 3B on the opposite side as shown in FIG. By making the scintillator 3A thinner than the scintillator 3B in this way, more X-rays reach the scintillator 3B, and the visible light exchanged by the scintillator 3A blurs before reaching the solid state detector. The visible light detection efficiency in the solid state detector can be improved.
[0043]
Further, in the above-described embodiment, as shown in FIG. 7, reflection layers 9A and 9B that reflect visible light may be provided outside the scintillators 3A and 3B. By providing the reflection layers 9A and 9B in this way, the visible light irregularly reflected in the scintillators 3A and 3B is reflected toward the solid detector 2 by the reflection layers 9A and 9B. Detection efficiency can be improved.
[0044]
In the above-described embodiments, the resin sheet is used as the substrate of the solid detector. However, the present invention is not limited to this, and quartz glass having a thickness of about several hundred microns that does not absorb the radiation image is used. An inorganic material such as the above may be used.
[0045]
Further, in the above-described embodiments, the amorphous silicon layer is used as the semiconductor layer, but the present invention is not limited to this, and any semiconductor layer may be used.
[0046]
【The invention's effect】
As described in detail above, the radiation image detector according to the present invention has a solid state detector disposed between two scintillators, and the radiation image detector is irradiated with radiation irradiated by the scintillator on the side irradiated with radiation. The radiation not converted by the scintillator on the side irradiated with radiation is converted into visible light by the scintillator on the opposite side to the side irradiated with radiation, and each visible light is detected by a solid state detector. is there. For this reason, the detection efficiency of the visible light converted by the scintillator is improved, the sharpness of the radiation image obtained by the radiation image detector according to the present invention can be improved, and a high-quality radiation image can be obtained as a whole. it can.
[Brief description of the drawings]
According to the invention; FIG part represents a solid state detector for use in an embodiment of the radiation image detector according to FIG. 2 shows the present invention which represents an embodiment of the radiation image detector according enlarged view the present invention; FIG partial enlarged view showing still another solid state detectors used in an embodiment of the radiation image detector according to some enlargement [4] the present invention representing another solid state detectors used in an embodiment of the radiation image detector diagram showing another embodiment of the radiation image detector according to some enlarged view the present invention; FIG representing yet another solid state detectors used in an embodiment of the radiation image detector according to the present invention; FIG Figure 7 is a diagram showing still another embodiment of the radiation image detector according to the present invention.
1 Radiation image detector 2 Solid state detector
3A, 3B Scintillator 4 X-ray source 5 X-ray 6 Subject 7 Information processing means 8 Reproduction means
9A, 9B Reflective layer
11A, 11B, 11C, 11D substrate
18A, 18B, 18C solid state detector
19 Copper plate

Claims (5)

Two planar scintillators that convert the irradiated radiation into visible light;
Two substrates each having a large number of solid-state detection elements are arranged so as to face each other, and visible light converted by the two scintillators is converted by the solid-state detection elements of the two substrates, respectively. A planar solid-state detector disposed between the two scintillators to obtain two electrical signals, and the radiation is substantially perpendicular to the plane of the two scintillators and the solid-state detector. A radiation image detector that is irradiated, wherein, among the two electric signals, the weight of the electric signal obtained from the visible light converted by the scintillator on the side irradiated with the radiation is used as the radiation irradiation side. Radiation characterized by comprising arithmetic means for adding the two electric signals so as to be larger than the weight of the electric signal obtained from the visible light converted by the scintillator on the opposite side Image detector. Two planar scintillators that convert the irradiated radiation into visible light;
A number of solid detection elements are formed on both surfaces of a single substrate, and the visible light converted by the two scintillators is converted by the solid detection elements on both surfaces of the substrate to obtain two electrical signals. A solid state detector disposed between two scintillators, and a radiation image detector formed by irradiating the radiation substantially perpendicularly to a plane of the two scintillators and the solid state detector. Of the two electric signals, visible light obtained by converting the weight of the electric signal obtained from the scintillator on the side irradiated with the radiation by the scintillator on the side opposite to the side irradiated with the radiation A radiation image detector, comprising arithmetic means for adding the two electric signals so as to be larger than the weight of the electric signal obtained from the above. Radiation image detector according to claim 1, wherein in that a light reflecting layer which reflects the visible light on the surface of the outer side of the two scintillators arranged the solid state detector between. Wherein the substrate, the radiation image detector of any one of claims 1 to 3, characterized in that a substance absorbs less of the radiation. The radiation image detector according to claim 4, wherein the substance that absorbs less radiation is a resin sheet.

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