JPH11237480A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector for a CT device having high sensitivity to radiation and corresponding to high resolution and high speed scanning. SOLUTION: A scintillator 3 with elements expressed by a general equation (Gd1-x-y-z Prx Rey Cez )2 O2 S where Re is at least one element selected from a group consisting of Dy, Nd, Sm, Ho, Er and Tm and 0.000003<=x<=0.2, 0,000001<=y<=0.001, and 0.000001<=z<=0.005 is optically contacted to a silicon photodiode and in between each scintillator, a separate plate 4 of molybdenum and the like for absorbing reflected light and scattered X-ray is arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radiation detector for detecting X-rays, and more particularly to a radiation detector used in an X-ray CT apparatus.

[0002]

2. Description of the Related Art As one of X-ray diagnostic apparatuses, there is a computed tomography apparatus (hereinafter referred to as a CT apparatus). The CT apparatus comprises an X-ray tube having a fan-shaped fan beam for irradiating X-rays and an X-ray detector provided with a number of X-ray detection elements, which are arranged opposite to the center of the tomographic plane of the subject. X-ray absorption data is collected by irradiating a fan beam X-ray from an X-ray tube toward the laser beam and changing the angle, for example, by one degree with respect to the tomographic plane each time irradiation is performed. The X-ray absorptance at each position on the tomographic plane is calculated by analyzing the data with a computer, and an image corresponding to the absorptivity is constructed.

Conventionally, a xenon gas detector has been used in this CT apparatus. This xenon gas detector encloses xenon gas in a gas chamber, applies voltage between a large number of arranged electrodes, and irradiates x-rays. When x-rays ionize xenon gas, a current signal corresponding to the intensity of x-rays Can be taken out, thereby forming an image. However, this xenon gas detector requires a thick window to enclose high-pressure xenon gas in the gas chamber, and thus has a problem that the use efficiency of X-rays is low and the sensitivity is low. Further, in order to obtain a high-resolution CT apparatus, it is necessary to reduce the thickness of the electrode plate as much as possible. If the electrode plate is made thinner as described above, there is a problem that the electrode plate vibrates due to external vibration and noise is generated. .

[0004]

On the other hand, CdWO ₄ single crystals and G
A detector that combines a ceramic scintillator sintered with d ₂ O ₂ S: Pr phosphor powder and a silicon photodiode has been developed and put into practical use. In a detector using these materials, it is easy to reduce the size of the detection element and increase the number of channels, so that it is possible to obtain an image with higher resolution than a xenon gas detector. However, in recent years, there has been a demand for further improvement in resolution and reduction of the radiation dose to the human body in CT apparatuses. In order to improve the resolution, it is necessary to further reduce the size of the element. However, when the element is reduced in size, the amount of X-rays incident on one element decreases, and the output decreases in a practically used scintillator, and sufficient resolution is obtained. There is a problem that can not be. In order to reduce the human exposure dose, it is necessary to shorten the scanning time.However, the time of one irradiation is shortened, and in this case, the output decreases with a practical scintillator, and There is a problem that resolution cannot be obtained. The present invention has been made in view of the above problems, and an object of the present invention is to provide a radiation detector for a CT apparatus compatible with high resolution and high speed scanning.

[0005]

Means for Solving the Problems To achieve the above object, the present inventors studied the composition of a scintillator and found that the general formula (Gd _1-xyz Pr) disclosed in Japanese Patent Application No. 9-33335 was disclosed.
_x Re _y Ce _z ) ₂ O ₂ S (where, in the above formula, Re is Dy, Nd, S
m, Ho, represents at least one element selected from the group consisting of Er and Tm, 0.000003 ≦ x ≦ 0.2, 0.000001 ≦ y ≦ 0.0
01, and a scintillator powder having a composition of 0.000001 ≦ z ≦ 0.005) is hot isostatically pressed (H
It has been found that a scintillator sintered by the IP) method is a scintillator suitable for a radiation detector of a CT apparatus. The present invention is a radiation detector characterized by using a combination of the scintillator and a photodetector that converts light of the scintillator into an electric signal.The radiation detector has a higher luminous efficiency than a conventional scintillator. High sensitivity. As a result, the resolution can be improved, and more accurate diagnosis can be performed. Also, by shortening the scanning time,
It is possible to reduce human exposure dose.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a radiation detector according to the present invention will be described below. FIG. 1 is an external view showing an embodiment of the radiation detector of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. A scintillator 3 is adhered to a silicon photodiode 2 formed on a glass epoxy substrate 1 with an optical epoxy resin. Between each scintillator, a separate plate 4 of molybdenum or the like is inserted for the purpose of reflecting light and absorbing scattered X-rays. Further, in order to prevent the light of the scintillator generated by the incident X-ray from leaking to the outside, a TiO ₂ powder is applied as a light reflection layer 5 on the top and the end face of the scintillator 3. The thickness t of the scintillator 3 shown in FIG. 2 is preferably 1.0 to 2.0 mm. When the thickness t of the scintillator is smaller than 1 mm,
The emission output of the scintillator decreases, and X-rays transmitted through the scintillator enter the silicon photodiode 2 to generate noise. The thickness t of the scintillator is 2m
If it is larger than m, the light transmittance of the scintillator is not large, so that the amount of light emitted from the upper part of the scintillator and incident on the silicon photodiode decreases, and the sensitivity of the radiation detector decreases. On the other hand, the width w of the scintillator is preferably from 0.5 to 1.5 mm. When the width w of the scintillator is smaller than 0.5 mm, the sensitivity of the radiation detector decreases, and the image quality of the tomographic image obtained by the X-ray CT apparatus decreases. When the width w of the scintillator exceeds 1.5 mm,
This is because the size of one element increases and the image resolution of the tomographic image decreases.

[0007]

Next, an embodiment of the radiation detector of the present invention will be described. (Example 1) The Gd ₂ O ₃ 362.14g, the Pr ₆ O ₁₁ 0.34g, and Sm ₂
The O ₃ was 0.0174g weighed. Next, Ce (NO ₃ ) ₃・
1.3 g of 6H ₂ O was dissolved, and 4 ml of the solution was added to the raw material with a pipette, followed by wet mixing and drying. Then, the raw materials, the Na ₂ CO ₃ 95.72g, 10.10g a Li ₂ B ₄ O _7, the K ₃ PO ₄ · 3H ₂ O
32.33 g and 105.49 g of S were added and dry mixed. next,
This raw material mixed powder was placed in an alumina crucible, covered with alumina, and fired at 1300 ° C. for 8 hours. After cooling, the crucible and the fired product were left in pure water for 1 hour to loosen the raw materials. This raw material is thoroughly washed with pure water, and then, using a stirrer, with 1N hydrochloric acid.
Washing was performed for 1 hour with warm water at 90 ° C. for 1 hour. Thus, (Gd _0.999 Pr _0.001 Sm _0.00005 Ce _0.000012 ) ₂ O _{2 having} an average particle size of 42 μm
S scintillator powder was obtained. 0.1% by weight of Li ₂ GeF ₆ was added to this powder as a sintering aid, and the powder was filled in a mild steel capsule and then vacuum sealed. Then, hot isostatic pressing (HIP) sintering was performed at 1350 ° C., 1000 atm, and 2 hours. The obtained sintered body was machined into a rod shape having a length of 30 mm, a width of 0.9 mm, and a thickness of 1.25 mm, and then heat-treated at 1100 ° C. for 1 hour in an Ar gas containing a small amount of oxygen to obtain a scintillator. The scintillators and molybdenum plates were alternately arranged and bonded to a silicon photodiode. Then, TiO ₂ powder was applied to the scintillator surface. Table 1 shows the characteristics of the obtained radiation detector.

(Example 2) A radiation detector was manufactured in the same procedure as in Example 1. However, instead of adding Sm ₂ O ₃ , 0.0168 g of Nd ₂ O ₃ was added, and (Gd _0.999 Pr _0.001 Nd _0.00005
A scintillator having a composition of Ce _0.000012 ) ₂ O ₂ S was used. Table 1 shows the characteristics of the obtained radiation detector.

Comparative Example 1 A radiation detector was manufactured in the same procedure as in Example 1. However, Sm ₂ O ₃ was not added, and a scintillator having a composition of (Gd _0.999 Pr _0.001 Ce _0.000012 ) ₂ O ₂ S was used. Table 1 shows the evaluation results of the characteristics. (Comparative Example 2) A radiation detector was manufactured in the same procedure as in Example 1. However, the scintillator has a thickness of 2 mm.
A CdWO ₄ single crystal scintillator was used. This radiation detector was used as a criterion for characteristic evaluation.

Table 1 shows the relative sensitivities of various radiation detectors. Here, the relative value of the signal output when X-rays (W target) with a tube voltage of 120 kV and a tube current of 5 mA are applied to various radiation detectors is shown.

[0011]

[Table 1]

[0012]

As is apparent from the detailed description of the present invention, it is possible to increase the sensitivity, improve the resolution of the CT apparatus, and realize high-speed scanning with respect to the conventional radiation detector.

[Brief description of the drawings]

FIG. 1 is an external view of a radiation detector according to the present invention.

FIG. 2 is a sectional view taken along line AA of the radiation detector according to the present invention.

[Explanation of symbols]

1 substrate, 2 silicon photodiode, 3 scintillator, 4 separate plate, 5 light reflection layer

Claims (3)

[Claims] 1. A radiation detector comprising a scintillator which emits light by irradiation with X-rays or the like and means for converting the amount of light emitted into an electric signal, wherein the scintillator has a general formula
_1-xyz Pr _x Re _y Ce _z ) ₂ O ₂ S, where Re is Dy, Nd, Sm, H
o, at least one element selected from the group consisting of Er and Tm, 0.000003 ≦ x ≦ 0.2, 0.000001 ≦ y ≦ 0.001,
And a composition in the range of 0.000001 ≦ z ≦ 0.005. 2. The radiation detector according to claim 1, wherein the composition of the scintillator is such that y in the general formula is in the range of 0.000001 ≦ y ≦ 0.0005. 3. The method according to claim 1, wherein
The scintillator has a width of 0.5 to 1.5 mm and a thickness of 1 to
A radiation detector characterized by being 2 mm.