JP2003240857A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector easy to fabricate and capable of high-resolution discrimination of the incidence position of radiation. <P>SOLUTION: Photomultipliers 2a-2d are optically coupled to a scintillator group 1 with the scintillators arranged two-dimensionally to contact with each other. Optically transparent or translucent separators 3, locally covered by light reflecting masks as required, are in close contact with the plane mounted with scintillators 1 a1-1 f8. The positions and sizes of masks on the separators 3 are changed, relative to the order of arrangement of the scintillators, so that the light to be guided to the photoelectric surfaces of the photomultipliers 2a-2d is changed corresponding to the incidence position of gamma rays. The incidence position of gamma rays is determined by comparing the outputs of the photomultipliers 2a-2d with each other. <P>COPYRIGHT: (C)2003,JPO

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, it detects radiation (gamma rays) emitted from a radioisotope (RI) that is administered to a subject and accumulated in the region of interest to detect the radiation of the region of interest. Device for obtaining tomographic image of RI distribution,
For example, the present invention relates to a radiation detector used in a positron CT device, a single photon ECT device, or the like.

[0002]

2. Description of the Related Art A radiation detector of this type includes a scintillator which emits light when gamma rays emitted from a subject are incident on the scintillator.
It is composed of a photomultiplier tube that converts the light emission of this scintillator into a pulsed electric signal. In such a radiation detector, conventionally, there was a one-to-one correspondence between the scintillator and the photomultiplier tube, but in recent years, a plurality of scintillators are combined with a smaller number of photomultiplier tubes,
The resolution is enhanced by adopting a method of determining the incident position of gamma rays from the output ratio of these photomultiplier tubes. By adopting such a system, various radiation detectors having a structure for appropriately distributing the light emitted from the scintillator to a plurality of photomultiplier tubes have been proposed, and
The configuration of a conventional radiation detector will be described with reference to the drawings.

A first conventional example (Japanese Patent Publication 2-1) shown in FIG.
The radiation detector (see Japanese Patent No. 4666) includes a scintillator group 11 including four scintillators 11a, 11b, 11c, and 11d, and two photomultiplier tubes 12a and 12b. In the scintillator group 11, the boundaries of the inner scintillators 11b and 11c are optically coupled with silicone grease or the like, and the boundaries of the outer scintillators 11a and 11b and the scintillator 11c are
The boundary of 11d is optically shielded by the reflective material 13. By configuring the boundaries of the scintillators 11a to 11d as described above, the output ratio of the photomultiplier tubes 12a and 12b is changed according to the incident position of gamma rays.

A second conventional example (Japanese Patent Publication No. 6-9) shown in FIG.
The radiation detector (see Japanese Patent No. 5146) includes a scintillator group 21 partitioned by a large number of slits, and four photomultiplier tubes 22a, 22b, 22c, 22d optically coupled to the scintillator group 21. It is configured. A reflective material 23 is provided in each slit of the scintillator group 21.
Is embedded. In this radiation detector, the incident position of gamma rays is discriminated by adjusting the length of each slit so that it becomes longer from the inner side to the outer side.

A third conventional example shown in FIG.
In the radiation detector (see Japanese Patent No. 185385), a plurality of scintillators have a coupling surface that is a rough surface and / or a mirror surface, and a scintillator group 31 that optically couples the coupling surfaces with an air layer interposed therebetween. , This scintillator group 31
Four photomultiplier tubes 32a, 32b, 32 coupled to
It is composed of c and 32d. In this radiation detector, by the surface state of two scintillators facing each other,
The incident position of gamma rays is discriminated by utilizing the fact that the light transmittance between the scintillators changes.

A fourth conventional example shown in FIG.
The radiation detector of JP-A-281362) has a scintillator group 41 in which an optical reflection material 43 (thickness 0.1 to 0.2 mm) is applied to a required area of a surface facing each scintillator.
And four photomultiplier tubes 42a, 42b, 42c, 42d coupled to the scintillator group 41. In this radiation detector, the incident position of gamma rays is discriminated by changing the area where the reflecting material 43 is applied in relation to the arrangement order of the scintillators.

[0007]

Although the conventional radiation detector is constructed as described above, each of the above conventional examples has the following problems. In the first conventional example shown in FIG. 8, the scintillator array is one for the photomultiplier tube.
Since it is dimensional, the number of photomultiplier tubes is large with respect to the number of scintillators, and there is a problem that the manufacturing cost of the radiation detector increases accordingly. In addition, since two photomultiplier tubes can be used to discriminate only four types of incident positions of gamma rays, there is a problem that the resolution is low.

On the other hand, in the second conventional example shown in FIG. 9, it is necessary to uniformly embed the reflecting material in the slit formed by processing the scintillator, but this kind of work is complicated and difficult. But also. Further, in order to obtain high resolution, it is necessary to form slits in the scintillator at a fine pitch, and at this time, there is a problem that the scintillator is easily damaged.

Further, in the third conventional example shown in FIG. 10, the surface of each scintillator needs to be changed variously, but since this kind of surface processing is complicated, the production cost of the radiation detector increases. There is a point. Further, in the fourth conventional example shown in FIG. 11, it is difficult to control the thickness of the reflective material to be applied, and there is a possibility that the accuracy of finishing when arrayed may be deteriorated. Further, there is a problem that uneven filling of the adhesive occurs in a portion where the reflective material is not applied, resulting in attenuation of the light quantity or deterioration of position calculation accuracy.

The present invention has been made in view of the above circumstances, and provides a radiation detector capable of discriminating the incident position of radiation with high resolution and being easily manufactured. Is intended.

[0011]

In order to achieve the above-mentioned object, the present invention provides a plurality of scintillators closely arranged two-dimensionally and is optically coupled to the scintillator group, and In a radiation detector having a plurality of photomultiplier tubes less than the number of scintillators, each of the scintillators face each other, an optically transparent or semitransparent separator with a light reflection mask in the required area. It is characterized in that they are in close contact with each other, and the position and size or the transmittance of the light reflection mask of the separator are changed in relation to the arrangement order of the scintillators.

In another embodiment of the present invention, 2
A plurality of scintillators closely arranged in a dimension, a plurality of light guides facing the scintillator group, optically coupled, and optically coupled to the light guide, and of the scintillator In a radiation detector having a plurality of photomultiplier tubes less than the number of the photomultiplier tubes, a light reflecting material is closely adhered between all of the scintillators, and the light guide masks are provided in required areas on the surfaces facing each of the light guides. It is characterized in that the applied optically transparent or semi-transparent separator is adhered, and the position and size or transmittance of the light reflection mask of the separator are changed in relation to the arrangement order of the scintillators. . Furthermore, as another embodiment, the light reflection mask applied to the separator is formed by vapor deposition of metal, the light reflection mask applied to the separator is a mirror surface or white, the scintillator or the light guide and the separator. Is adhered with an optical adhesive, and a white light reflection mask having an optical blocking layer or a mirror surface layer formed in the middle is used as the light reflection material.

Since the radiation detector of the present invention is constructed as described above and uses the optically transparent or semi-transparent separator having a light reflection mask in the required area, the radiation detector is different from the conventional radiation detector. It is easy to manufacture, and the finishing accuracy of the array can be increased, so that the position calculation accuracy can be improved.

[0014]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the radiation detector of the present invention will be described below with reference to the drawings. 1 is an external perspective view of an embodiment of the radiation detector according to the present invention, FIG. 2 is a detailed view of a separator used in the radiation detector of FIG. 1, and FIG. 3 is an arrow AA of the radiation detector of FIG. FIG. The radiation detector of this embodiment has a scintillator group 1 in which a total of 48 scintillators 1 _a1 to 1 _f8 , six scintillators 1 _a1 to 1 _f8 in the X direction and eight in the Y direction, are closely arranged in a two-dimensional manner. Four photomultiplier tubes 2a, 2 optically coupled together
b, 2c, and 2d. Examples of the scintillator include Bi ₄ Ge ₃ O ₁₂ (BGO) and Gd ₂ S.
Inorganic crystals such as iO ₅ (GSO), NaI, BaF ₂ and CsF are used.

A separator 3 as shown in FIG. 2 is adhered to each surface of the scintillators 1 _a1 to 1 _f8 excluding the bonding surface with the photomultiplier tube by a light-transmissive adhesive. This separator 3 is made of transparent PE as shown in FIG.
Aluminum deposition part 5 with aluminum deposited on both sides of T film 4
Is formed. The area of the aluminum vapor deposition portion 5 is changed in relation to the arrangement order of the scintillators 1 _a1 to 1 _f8 .

That is, as shown in FIG. 3 which is a sectional view taken along the line AA of the radiation detector of FIG. 1, for example, scintillators 1 _ai to 1 _fi (i is 1 to 8 are arranged in the X direction). The ratio of the light reflection mask portion (portion having an aluminum vapor deposition surface) and the transparent portion (portion having no aluminum vapor deposition surface) of the separator 3 to be inserted on the surfaces facing each other is the photoelectrons arranged in the X direction. Multiplier tube 2a (2d) and photomultiplier tube 2
The output ratio of b (2c) is experimentally determined so as to change at a constant rate. Assuming that the output of the photomultiplier tube 2a is Pa and the output of the photomultiplier tube 2b is Pb, (Pa−Pb) / (Pa + Pb) is the scintillator 1 _ai ...
The area of the mask portion of the separator 3 (the area of the aluminum vapor deposition portion 5) was determined so that it changed at a constant rate depending on the position of 1 _fi .

The ratio of the mask portion to the transparent portion of the separator 3 differs depending on the width W and height H of the scintillator. For example, when the width W is 3.7 mm and the height H is 30 mm, the scintillator faces each other. The ratio of forming the aluminum vapor-deposited surface with respect to the entire surface to be formed is 90 to 100% between the scintillators 1 _ai and 1 _bi in FIG. 3 and 30 to 40% between 1 _bi and 1 _ci.
0 to 5% between _ci and 1 _di , 30 to between 1 _di and 1 _ei
40%, 90-100% was suitable between 1 _ei and 1 _fi .

Scintillators 1 _j1 to 1 arranged in the Y direction
Similarly, in the case of _j8 (where j is any of a to f), the photomultiplier tubes 2a (2b) and the photomultiplier tubes 2 arranged in the Y direction are also arranged.
A photomasked separator is inserted at an appropriate ratio on the facing surfaces of the scintillators 1 _j1 to 1 _j8 so that the output ratio of d (2c) changes at a constant ratio.

In FIGS. 1, 2 and 3, the thickness of the separator 3, that is, the transparent PET film 4 and the aluminum vapor deposition portion 5 is emphasized, but in reality, the transparent PET is used.
The film 4 has a thickness of approximately 0.1 mm, and the aluminum vapor deposition part 5 has a vapor deposition thickness of approximately 0.5 μm. The outer surfaces of the scintillators 1 _a1 to 1 _{f8 which} are not opposed to each other are covered with a separator 3 which is vapor-deposited with aluminum except for the optical coupling surface with the photomultiplier tube.

Next, the operation of the above radiation detector will be described with reference to FIG. Now, _assume that a gamma ray is incident on the scintillator 1 _ci . This gamma ray is scintillator 1 _ci
It is absorbed inside and emits light. This light is scintillator 1 _ci
While being repeatedly reflected by the aluminum vapor-deposited surfaces of the separators provided on both surfaces of the photomultiplier, the light is guided to the photocathode of the photomultiplier tube 2a. At this time, a part of the light in the scintillator 1 _ci is also diffused to the adjacent scintillators 1 _bi and 1 _di via the transparent portion of the separator 3. The interface between the scintillator 1 _ci and 1 _di, compared to the interface between the scintillator 1 _bi and 1 _ci, since there are many portions of the transparent portion, the light in the scintillator 1 _ci diffuses much towards the scintillator 1 _di , A considerable amount of light is also guided to the photocathode of the photomultiplier tube 2b. As a result, the amount of light having a distribution according to the incident position of gamma rays is guided to each photomultiplier tube 2a, 2b. On the other hand, when the gamma ray is incident on the scintillator 1 _ai at the end, most of the light is photoelectron-enhanced because there are few transparent parts (unmasked regions) on the facing surfaces of the scintillators 1 _ai and 1 _bi. It is guided to the double tube 2a.

FIG. 4 is a block diagram showing a schematic configuration of a position detection calculation unit for detecting the incident position of gamma rays based on the outputs of the photomultiplier tubes 2a to 2d. As shown in the figure, in order to detect the incident position of the gamma ray in the X direction,
The output Pa of the photomultiplier tube 2a and the output Pd of the photomultiplier tube 2d are input to the adder 61, and the output Pb of the photomultiplier tube 2b and the output Pc of the photomultiplier tube 2c are added to each other. Entered in. The addition outputs Pa + Pd and Pb + Pc of both adders 61 and 62 are input to the position discriminating circuit 71, and the incident position of the gamma ray in the X direction is obtained based on the ratio of both addition outputs. Similarly, in order to detect the incident position of the gamma ray in the Y direction, the output P of the photomultiplier tube 2a is
a and the output Pb of the photomultiplier tube 2b are input to the adder 63, and the output Pd of the photomultiplier tube 2d and the output Pc of the photomultiplier tube 2c are input to the adder 64. Each addition output Pa + Pb and Pc + Pd of both adders 63 and 64
Are input to the position discriminating circuit 72, and the incident position of the gamma ray in the Y direction is obtained based on the ratio of both addition outputs.

In the above embodiment, the light in the scintillator group 1 is directly guided to the photomultiplier tubes 2a to 2d. However, if there is local sensitivity unevenness on each photocathode, the amount of incident light and the photomultiplier tube are increased. Since the relationship with the outputs of 2a to 2d changes, the detection accuracy of the incident position of the gamma ray decreases. In such a case, a light guide made of, for example, a transparent acrylic resin plate is inserted between the scintillator group 1 and the photomultiplier tubes 2a to 2d, and the light in the scintillator group 1 is passed through this light guide. It may be guided to the photomultiplier tubes 2a to 2d. In this way, by using the light guide,
Since the light incident on each photocathode of the photomultiplier tubes 2a to 2d is dispersed, local sensitivity unevenness on the photocathode is suppressed, and the detection accuracy of the incident position of the gamma ray can be improved.

Further, in the above-described embodiment, the position and area of the mask portion provided on the separator inserted in each facing surface of the scintillator were changed, but as shown in FIG. 5, the entire surface of the separator inserted between each scintillator is changed. Similar effects can be obtained by depositing aluminum, changing the thickness of the deposited aluminum film in relation to the arrangement order of the scintillators, and changing the light transmittance thereof. In the embodiment shown in FIG. 5, the transmittance is 0%, the transmittance is 50%, the transmittance is 90%, the transmittance is 50%, and the transmittance is 0%, but the transmittance value is not limited to this. The output ratio of the photomultiplier tube 2a (2d) and the photomultiplier tube 2b (2c) can be appropriately experimentally determined so as to change at a constant rate depending on the incident position of the gamma ray.

Next, another embodiment of the radiation detector of the present invention will be described with reference to FIG. In FIG. 6, a white reflective film or a light-reflecting material 7 that has been entirely subjected to a light-reflecting mask is closely attached between the scintillators of the scintillator group 1. A plurality of light guides 6 face each scintillator and are optically coupled. Each light guide 6
A transparent separator 3 provided with a light reflection mask in a required area is closely attached to the surfaces facing each other.
By changing the position and size of the light reflection mask of 1 in relation to the arrangement order of the scintillators, the same effect as that of the radiation detector of FIG. 1 can be obtained. When a white reflective film is used as the light reflecting material 7, when 0.1 mm to 0.2 mm, which is the substantial thickness, light generated in the scintillator leaks to the adjacent scintillator to some extent, causing crosstalk, which results in positional resolution. As shown in FIG. 7, after forming the aluminum vapor deposition surface 5 on one surface of the two white PET films 8 and then adhering the light shielding layer (aluminum vapor deposition film 0.5 μm thick). By providing this and using this as the light reflecting material 7, crosstalk can be prevented.

In the above embodiment, the radiation detector constructed by optically coupling 48 scintillators and 4 photomultiplier tubes has been described as an example. However, the present invention is not limited to this.
The number of scintillators and photomultiplier tubes is not limited to this, and can be set arbitrarily. In addition, although the aluminum vapor-deposited portions are formed on both surfaces of the transparent PET film in the embodiments of FIGS. 1 to 3, the aluminum vapor-deposited portions can be provided on only one surface to obtain a sufficient effect. The same effect can be obtained even if a semitransparent member is used as the constituent member.

[0026]

As described above, the radiation detector of the present invention is such that a plurality of scintillators each have an optically transparent or semi-transparent separator provided with a light-reflective mask in a required area on the surface facing each other, Further, since the position and size of the light reflection mask of the separator or the transmittance is changed in relation to the arrangement order of the scintillators, the position and area of the light reflection mask of the separator or the transmittance of each scintillator are finely divided. By changing it, the incident position of the gamma ray can be accurately detected. Further, since a masked separator is inserted between a plurality of scintillators, it is easier to manufacture as compared with the conventional example, and further, the finishing accuracy of the array is increased, so that the position calculation accuracy is improved. Therefore, a high-resolution radiation detector can be easily realized at low cost.

[Brief description of drawings]

FIG. 1 is an external perspective view of an embodiment of a radiation detector of the present invention.

FIG. 2 is a diagram showing a separator used in the radiation detector of FIG.

3 is a cross-sectional view taken along the line AA of the radiation detector of FIG.

FIG. 4 is a block diagram showing a schematic configuration of a position detection calculation unit.

FIG. 5 is a diagram showing another embodiment of the separator used in the radiation detector of the present invention.

FIG. 6 is an external perspective view of another embodiment of the radiation detector of the present invention.

FIG. 7 is a diagram showing a configuration of a light reflecting material used in the radiation detector of FIG.

FIG. 8 is an external perspective view of a first conventional radiation detector.

FIG. 9 is an external perspective view of a second conventional radiation detector.

FIG. 10 is an external perspective view of a third conventional radiation detector.

FIG. 11 is an external perspective view of a fourth conventional radiation detector.

[Explanation of symbols]

1 scintillator group 2a-2d photomultiplier tube 3 separator 4 Transparent PET film 5 Aluminum vapor deposition department 6 Light guide 7 Light reflector 8 White PET film

Claims (6)

[Claims] 1. A plurality of scintillators closely arranged two-dimensionally and optically coupled to the scintillator group,
And, in a radiation detector having a plurality of photomultiplier tubes less than the number of the scintillators, the respective scintillators face each other, optically transparent or semi-transparent with a light reflection mask in a required area. The radiation detector is characterized in that the separator is closely attached, and the position and size or the transmittance of the light reflection mask of the separator are changed in relation to the arrangement order of the scintillators. 2. A plurality of scintillators closely arranged two-dimensionally, a plurality of light guides facing the scintillator group and optically coupled, and optically coupled to the light guides, In a radiation detector provided with a plurality of photomultiplier tubes less than the number of the scintillators, a light reflecting material is brought into close contact with all of the scintillators, and the light guides are respectively opposed to each other.
Adhering an optically transparent or semi-transparent separator provided with a light reflection mask in a required area, and changing the position and size or transmittance of the light reflection mask of the separator in relation to the arrangement order of the scintillators. A radiation detector characterized in that 3. The radiation detector according to claim 1, wherein the light reflection mask formed on the separator is formed by vapor deposition of metal. 4. The radiation detector according to claim 1, wherein the light reflection mask applied to the separator is a mirror surface or white. 5. The radiation detector according to claim 1 or 2, wherein the scintillator or the light guide and the separator are bonded together by an optical adhesive. 6. The radiation detector according to claim 2, wherein a white light reflection mask having an optical blocking layer or a mirror surface layer formed in the middle is used as the light reflecting material. vessel.