JPH049688A - Detector for x-ray ct device - Google Patents

Abstract

PURPOSE:To prevent the drop of detecting sensitivity and to suppress the influence of radiant ray deterioration upon scintillators by arranging photodiodes on the X-ray projection side of scintillators and forming a reflection layer containing phosphors on the X-ray incident side of the scintillators. CONSTITUTION:Plural scintillators 18 are arranged on the outside of the photodiode array 17 through spacers 19 and the light reflecting layer 20 is formed so as to cover both the scintillators 18 and the spacers 19. Respective scintillators 18 receiving X rays generate light corresponding to the intensity of X rays and the light is reflected by the layer 20 and reached to the photodiodes 17a, which output electric signals corresponding to the quantity of light to the scintillators 18. On the other hand, the layer 20 of a detector emits light with a wavelength capable of decoloring the color generated in the scintillator 18. Since the color generated in the scintillators 18 is decolored by the light of the specific wavelength generated from the layer 20, the drop of sensitivity of the detector can be suppressed.

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a detection device for an X-ray CT apparatus. (Prior Art) In an X-ray CT apparatus, an X-ray source and a detection device are arranged opposite to each other with a patient in between, and the X-ray source and detection device are rotated around the patient to transmit X-rays from the X-ray source to the patient. Rotational tomography is performed by emitting X-rays and receiving the X-rays that have passed through the patient with a detection device. Conventionally, the detection device used in this X-ray CT device is generally an ionization chamber type, but recently a solid-state type using a detection element array that combines a scintillator and a photodiode as a light receiving element has been used. A detection device has been proposed. In this solid-state detection device, when X-rays that have passed through the patient enter the scintillator of the detection element array, the scintillator emits light, which is detected by a photodiode. , small and S/
It has the characteristics that an image with a high N ratio and high sharpness can be obtained. (Problems to be Solved by the Invention) However, after repeated experiments in which this solid-state detection device was installed in an X-ray CT apparatus to perform X-ray photography, it was found that the following problem occurred. That is, scintillators used in solid-state detection devices have a phenomenon called radiation deterioration or X-ray exposure history. This phenomenon is one of the physical properties of scintillator materials, and it is necessary to suppress the influence of this phenomenon as much as possible. Radiation deterioration in the scintillator and the effects of this radiation deterioration will be explained. Radiation deterioration in a scintillator is a phenomenon in which when a scintillator material has lattice defects, it is colored by X-ray irradiation and the optical output is reduced by absorbing the generated visible light. This results in a decrease in the sensitivity of the detector array. As an effect of this decrease in sensitivity, X-ray CT
Variations in CT values and artifacts (pseudo-images) occur in the device. FIG. 6 shows a state in which X-rays are irradiated from the X-ray tube 1 to a subject 2, and the X-rays transmitted through the subject 2 are received by the detection device 3 and detected. As shown in this figure, when photographing a large subject 2B after photographing a small subject 2A several times, the channel 3a of the detection device 3 that was involved in the small subject 2A (which was in the shadow) is Subject 2 outside
Since the amount of X-ray irradiation is smaller than that of the channel of the detection device 3 that is not in the shadow of B, the sensitivity decreases less. Conversely, the sensitivity of the outer detection device channels is greatly reduced. The detection device 3, which had uniform sensitivity between each channel before photographing, has a step-like sensitivity distribution between channels after photographing two small subjects. If a large object 2B is photographed at this time, artifacts will appear due to the difference in sensitivity. If only a large object is photographed from the beginning, there will be no difference in sensitivity in the detection device, but the sensitivity of all the detection devices will uniformly decrease, causing the above-mentioned CT value fluctuation. The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a detection device for an X-ray CT apparatus in which the influence of radiation deterioration of a scintillator is suppressed. [Structure of the Invention] (Means and Effects for Solving the Problems) The inventor of the present invention has conducted various studies on the phenomenon in which scintillary sensitivity decreases in solid-state detection devices. The inventor investigated the relationship between the X-ray irradiation dose received by the scintillator and the detection sensitivity of the detection device. Generally, as shown in FIG. 4, as the amount of X-ray irradiation increases, the detection sensitivity of the detection device decreases. However, as shown in Figure 5, when the scintillator is colored by X-ray irradiation and the detection sensitivity is reduced, when light of a certain wavelength is irradiated, the scintillator fades and the colored state of the scintillator disappears, resulting in detection. A phenomenon in which the sensitivity returned to its original level was confirmed. The inventor focused on utilizing this phenomenon in which the colored state of a scintillator disappears due to light of a certain specific wavelength as a means for avoiding the influence of a decrease in detection sensitivity of the scintillator due to X-ray irradiation. They have also discovered that a light reflecting layer formed on the surface of the scintillator is used as a simple and reliable method for causing the above-mentioned recovery phenomenon by irradiating the scintillator with light of a certain wavelength. However, the detection element array used in the detection device is composed of a photodiode array provided on a substrate and a scintillator superimposed on the photodiode array, and the photodiode detects the light emitted by the scintillator when it receives X-rays. be. For this reason, a light reflecting layer is provided on the X-ray incident surface of the scintillator in order to efficiently condense the light emitted by the scintillator onto the photodiode. Therefore, by using a substance that emits light at a wavelength that can cause the above-mentioned recovery phenomenon in the scintillator for this light-reflecting layer, when the light-reflecting layer receives X-rays, the light-reflecting layer causes the scintillator to recover. It is possible to emit light at a certain wavelength and feed it to the scintillator. It was also found that the wavelength of light that can cause a recovery phenomenon in the scintillator is in the same range as the wavelength of light emitted from the phosphor. Among them, as a phosphor (La
It was found that the wavelength of CePr)F is suitable. This is because the sensitivity of the photodiode is at the minimum wavelength. Therefore, when the light-reflecting layer of the scintillator is formed of a material containing a phosphor, when the light-reflecting layer receives X-rays, the light-reflecting layer generates light that can erase and fade the coloring in the scintillator. Then, the scintillator that receives the light emitted from the light reflection layer loses its colored state, fades, and returns to its original state. The present invention has been made based on this knowledge. The detection device of the X-ray CT apparatus of the present invention has the following features:

[/-A photodiode stacked on the evening X-ray emission side, and a reflective layer containing a phosphor is formed on the X-ray incident side of the scintillator. (Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figure 2 is a cross-sectional view showing the solid-state detection device of this embodiment.
The figure is an enlarged 7-inch cross-sectional view of the scintillator. In the figure, 11ζJ: 7 meters, a large number of plates 1.2 arranged in an arc shape in an upright state, a holder made of arc-shaped lead that supports the upper ends of the large number of plates 12] 3, and a large number of plates 12, and a holder 14 made of arc-shaped lead that supports the lower end of the holder 12. Reference numeral 15 denotes a detection element array, and a plurality of detection element arrays are arranged on the outer circumferential side of the collimator 1 in its longitudinal direction. The configuration of one detection element γ ray] 5 will be explained. 16 is a vertically long board, and wiring is formed in a predetermined manner on this board 16. A photodiode array 7 is provided on the surface of the plate 12 at a position opposite to the row 1, and this photodiode array 17 has a plurality of photodiodes 17a arranged side by side. - A plurality of scintillators] 8 are arranged on the outer surface of the door L/A] 7 with spacers 19 interposed therebetween.
Furthermore, a light reflecting layer 20 is provided covering the scintillator I/-ta 172 and the spacer 18. This light reflecting layer 20 is made of (La Ce Pr)F. An intensifying screen made of phosphor is connected to a scintillator 17 and a spacer 1.
8 and adhered with adhesive. The fermentation wavelength of this <La Ce Pr) F, phosphor is 280
It is ll1m. Note that the photodiodes 17. of the photodiode array 17. a is this (La Ce P
r) Light at the wavelength of F3 phosphor 1. Sensitivity to ``is low.'' Furthermore, by increasing the thickness of layer 1) of the photodiode 17a, the wavelength sensitivity of this (La Ce Pr) F,+ phosphor can be eliminated. 7. Then, each detection element r-ray 15 is placed on a substrate] 6, and the side edges on both sides of the substrate 16 are brought into contact with each other so that = 1 meter 1
1 are arranged side by side in the longitudinal direction. One operation of the detection device configured as described above will be explained. In an X-ray CT device, an X-ray tube irradiates a subject with X-rays. The X-rays that have passed through the object pass through the collimator 1 of the detection device, where scattered components are removed. Next, the X-ray is scintillated

[/-] The light passes through the light reflection layer 20 provided on the front surface of the scintillator J8 and enters each part of the scintillator J8. Each part of the scintillator which received the X-rays emits light according to the intensity of the X-rays [2, This light is reflected by the light reflecting layer 20] Each of the photodiodes of 7 It reaches 1.7a. Each photodiode 17a outputs an electric signal corresponding to the amount from the wrench 1 and 18. Showed off by Kosai'1
A tomography scan of the i7 body will be performed. However, when the scintillator 8 of the detection device is irradiated with X-rays, coloring occurs. When the scintillator 18 becomes colored, it absorbs visible light generated by itself. For this reason,
The optical output of the scintillator 18 is reduced, and the degree to which the photodiode 1.7a receives light from the scintillator 8 and converts it into a °C electric signal also becomes low. On the other hand, the light reflecting layer 20 i of the detection device;! When receiving X-rays from the collimator 11, the coloring generated on the light reflection layer 20 or the scintillator 8 disappears, and light with a wavelength 1 or 2 times higher is emitted. -ru. Eliminate the coloring generated on the scintillator 18 from the light reflective layer 201. 7. When the scintillator 18 enters the scintillator 18, the colored state of the scintillator 18 disappears and fades, and the scintillator 8 recovers to its uncolored state. Therefore, the generated visible light 17 is not absorbed by the scintillator 18 and reaches each photodiode 17a of the photodiode array 7. As a result, each photodiode 17a receives light from the scintillator 18 and outputs an electric signal in its original state. The coloration generated in the scintillator 18 in this way is eliminated by light of a specific wavelength emitted by the light reflection layer 20, thereby maintaining the scintillator 18 in its original uncolored state and suppressing a decrease in sensitivity as a detection device. I can do it. Therefore, by preventing radiation deterioration of the scintillator 18, it is possible to prevent, for example, from photographing a large subject after photographing a small subject. Note that the phosphor used in the light reflection layer of the scintillator is not limited to (La Ce Pr) Fi shown in the example. The form in which the light reflecting layer is provided with the phosphor is not limited to the embodiment. [Effects of the Invention] As explained above, according to the detection device of the X-ray CT apparatus of the present invention, since the light reflection layer is provided with a phosphor that emits light of a wavelength that eliminates the colored state of the scintillator, It is possible to suppress the effects caused by the coloring of the scintillator due to the coloring of the scintillator.

[Brief Description of the Drawings] Fig. 1 is a sectional view of the detection element array, Fig. 2 is a sectional view of the detection device seen from the side, Fig. 3 is a perspective view of the detection device, and Fig. 4 is a sectional view of the detection element array.
The figure is a diagram showing the relationship between the X-ray irradiation dose to the detection device and the sensitivity of the detection device, Figure 5 is a diagram showing the relationship between the light irradiation dose to the detection device and the sensitivity of the detection device, and Figure 6 is a diagram showing the relationship between the X-ray irradiation dose to the detection device and the sensitivity of the detection device. It is an explanatory view showing the state of X, *irradiation to the device. 11... Collimator, 15... Detection element array, 1
6... Substrate, 17... Photodiode array, 1
8...Scintillator, 20...Light reflecting layer. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 2 Figure

Claims (2)

[Claims] (1) An X-ray CT comprising a scintillator and a photodiode located on the X-ray emission side of the scintillator, and a reflective layer containing a phosphor is provided on the X-ray incident side of the scintillator. Device detection device. (2) The detection device for an X-ray CT apparatus according to claim 1, wherein the light reflecting layer contains (LaCePr)F_3.