Radiation detector and positron emission tomography device

Abstract

The objective is to provide a radiation detector or the like that can adjust the DOI separation characteristics of the radiation detector. [Solution] A radiation detector 1 comprises at least two scintillator sections arranged in parallel with each other, a scintillator 10 configured to allow light to flow between one end of each of the at least two scintillator sections, and a photodetection unit 20 optically connected to the other end of each of the at least two scintillator sections, wherein the scintillator includes a structure BT that controls the amount of scintillation light flowing through the scintillation light generated within the scintillator.

Description

[Technical Field]

[0001] This disclosure relates to a radiation detector and a positron emission tomography device. [Background technology]

[0002] A radiation detector is known that has a scintillator (U-shaped scintillator) having two scintillator sections arranged in parallel with each other, and configured so that light (scintillation light) can flow between one end of each of these two scintillator sections (see, for example, Patent Document 1). The scintillator section of Patent Document 1 is divided into multiple segments by a modified region (a light scattering region where the transmittance of light differs depending on the angle of incidence) formed by laser irradiation. By forming this modified region, the proportion of scintillation light reaching both ends of the scintillator changes for each segment in which scintillation light is generated. Therefore, by performing a predetermined calculation based on the output of a photodetector optically connected to both ends, the segment in which scintillation light was generated can be identified. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6726969 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, Patent Document 1 does not mention anything about adjusting the DOI separation characteristics of the radiation detector, and improvement is desired.

[0005] This disclosure is made to solve these problems and aims to provide a radiation detector and a positron emission tomography system that can adjust the DOI separation characteristics of the radiation detector. [Means for solving the problem]

[0006] A radiation detector according to a first aspect of the embodiment comprises at least two scintillator sections arranged in parallel with each other, a scintillator configured to allow light to flow between one end of each of the at least two scintillator sections, and a photodetection unit optically connected to the other end of each of the at least two scintillator sections, wherein the scintillator includes a structure that controls the amount of scintillation light flowing through the scintillation light generated within the scintillator.

[0007] Alternatively, a positron emission tomography apparatus according to a second aspect of the embodiment comprises a subject holding bed for holding a subject administered a radioactive drug, a ring-shaped radiation detector for detecting radiation emitted from the subject, means for identifying the location of the radiation emission site based on the output of the radiation detector, means for generating an image showing the location of the emission site, and a display device for displaying the image, wherein the radiation detector comprises at least two scintillator sections arranged in parallel with each other, a scintillator configured to allow light to flow between one end of each of the at least two scintillator sections, and a photodetection unit optically connected to the other end of each of the at least two scintillator sections, and the scintillator includes a structure for controlling the amount of scintillation light flowing within the scintillator.

[0008] According to the first or second aspect described above, the DOI separation characteristics of the radiation detector can be adjusted by a structure that controls the amount of scintillation light flowing within the scintillator.

[0009] Furthermore, in the first or second aspect described above, it is also preferable that the structure is such that the spacing between peaks in the multi-peaked DOI separation characteristic histogram is wider than in the case where the structure is not provided. In this way, the spacing between peaks in the DOI separation characteristic histogram can be widened by adjusting the DOI separation characteristics.

[0010] Furthermore, in the first or second aspect described above, it is also preferable that the structure is a light-absorbing material that absorbs at least a portion of the scintillation light generated within the scintillator. This is an example of such a structure.

[0011] Furthermore, in the first or second aspect described above, the light-absorbing material may preferably be black tape or black paint. This is just one example of a light-absorbing material. The light-absorbing material may be something other than black tape or black paint.

[0012] Furthermore, in the first or second aspect described above, it is also preferable that the structure is a light scattering material that scatters at least a portion of the scintillation light generated within the scintillator. This is an example of such a structure.

[0013] Furthermore, in the first or second aspect described above, the light scattering material may also preferably be a notch formed in the scintillator, a rough surface that functions as a light scattering surface, or a laser-processed surface that functions as a light scattering surface. This is just one example of a light scattering material. The light scattering material may also be something other than a notch formed in the scintillator, a rough surface that functions as a light scattering surface, or a laser-processed surface that functions as a light scattering surface.

[0014] Furthermore, in the first or second aspect described above, it is preferable that the structure is such that the spacing between peaks in the multi-peaked DOI separation characteristic histogram becomes narrower compared to the case where the structure is not provided. In this way, the spacing between peaks in the DOI separation characteristic histogram can be narrowed by adjusting the DOI separation characteristics.

[0015] Furthermore, in the first or second aspect described above, the structure may also preferably be a diffuse reflector that diffusely reflects the scintillation light generated within the scintillator. This is an example of such a structure.

[0016] A radiation detector according to an embodiment is the radiation detector according to [1], comprising: at least two scintillator portions arranged in parallel to each other; a scintillator configured to allow light to flow between respective one end portions of the at least two scintillator portions; and a light detection unit optically connected to respective the other end portions of the at least two scintillator portions, wherein the scintillator includes a structure that controls a flow amount of scintillation light generated inside the scintillator.

[0017] The radiation detector according to the embodiment may be the radiation detector according to [2] above, wherein the structure is a structure that makes an interval between peaks of a multimodal DOI separation characteristic histogram wider than that in a case where the structure is not provided, as described in [1] above.

[0018] The radiation detector according to the embodiment may be the radiation detector according to [3] above, wherein the structure is a light absorbing material that absorbs at least part of the scintillation light generated inside the scintillator, as described in [2] above.

[0019] The radiation detector according to the embodiment may be the radiation detector according to [4] above, wherein the light absorbing material is black tape or black coating, as described in [3] above.

[0020] The radiation detector according to the embodiment may be the radiation detector according to [5] above, wherein the structure is a light scattering material that scatters at least part of the scintillation light generated inside the scintillator, as described in [2] above.

[0021] The radiation detector according to the embodiment may be the radiation detector according to [6] above, wherein the light scattering material is a notch portion formed in the scintillator, a rough surface functioning as a light scattering surface, or a laser-processed surface functioning as a light scattering surface, as described in [5] above.

[0022] The radiation detector according to the embodiment may be the radiation detector according to [7] above, wherein the structure is a structure that makes an interval between peaks of a multimodal DOI separation characteristic histogram narrower than that in a case where the structure is not provided, as described in [1] above.

[0023] The radiation detector according to the embodiment may be the radiation detector according to the above [7], wherein the structure is a diffuse reflector that diffusely reflects scintillation light generated in the scintillator, as described in [8].

[0024] The positron emission tomography apparatus according to the embodiment may be the positron emission tomography apparatus according to [9], comprising: a subject holding bed that holds a subject to which a radiopharmaceutical is administered; radiation detectors arranged in a ring shape to detect radiation generated from the subject; means for identifying the position of a radiation emission site based on an output of the radiation detectors; means for generating an image indicating the position of the emission site; and a display device for displaying the image, wherein each of the radiation detectors comprises at least two scintillator sections arranged in parallel to each other, a scintillator configured to allow light to flow between respective one ends of the at least two scintillator sections, and a light detection unit optically connected to the respective other ends of the at least two scintillator sections, and the scintillator includes a structure that controls the flow rate of scintillation light generated inside the scintillator. Effects of the Invention

[0025] According to the present disclosure, a radiation detector capable of adjusting the DOI separation characteristics of the radiation detector, and a positron emission tomography apparatus can be provided. Brief Description of the Drawings

[0026] [Figure 1] This is a schematic configuration diagram of the radiation detector 1 according to the first embodiment. [Figure 2] This is a perspective view of the scintillator 10 and a part of the light detection unit 20 extracted from Figure 1. [Figure 3] This is a histogram summarizing the calculation results of DOI information. [Figure 4] This is an example of a positron emission tomography apparatus 60 to which the radiation detector 1 of the present disclosure is applied. [Figure 5]This is an example of a positron emission tomography apparatus 60 to which the radiation detector 1 of this disclosure is applied. [Figure 6] (a) An example of a scintillator 10B in which the second scintillator block 13 is divided between segment (2) and segment (3) to form two scintillator blocks 13A and 13B, with an air layer between one scintillator block 13A and the other scintillator block 13B. (b) An example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in a 360-degree direction is placed and radiation (gamma rays) is uniformly irradiated onto the radiation detector 1 in Figure 6(a) for a certain period (approximately 3 minutes). [Figure 7] (a) An example in which black tape BT is attached to the upper surface of the second scintillator block 13, and (b) an example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in a 360-degree direction is placed and radiation (gamma rays) is uniformly irradiated onto the radiation detector 1 in Figure 7(a) for a certain period (approximately 3 minutes). [Figure 8] (a) An example in which the black tape BT is attached to the top and side surfaces of the second scintillator block 13, (b) An example in which the black tape BT is attached to the bottom surface of the second scintillator block 13, (c) An example in which the black tape BT is attached to the bottom and side surfaces of the second scintillator block 13, (d) An example in which the black tape BT is attached to the top, bottom, and side surfaces of the second scintillator block 13, and (e) An example in which the black tape BT is attached off-center. [Figure 9] (a)(b) This is an example in which the notched section NT is used instead of the black tape BT. [Figure 10](a) An example in which the second scintillator block 13 is divided between segment (2) and segment (3) to form two scintillator blocks 13A and 13B, with an air layer between one scintillator block 13A and the other scintillator block 13B, and the top and sides of the second scintillator block 13 are covered with a specular reflective material, a reflective member 40 (e.g., ESR). (b) An example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in a 360-degree direction is placed and radiation (gamma rays) is uniformly irradiated onto the radiation detector 1 in Figure 10(a) for a certain period (approximately 3 minutes). [Figure 11] (a) A scintillator with a configuration similar to the scintillator shown in Figure 10(a), (b) an example of a U-shaped scintillator formed by creating a notch in a single scintillator block, and (c) an example of a scintillator similar to the scintillator described in Patent Document 1. [Figure 12] This is a perspective view of the modified scintillator 10A. [Figure 13] This is a schematic perspective view of a radiation detector 2 using a modified scintillator 110. [Figure 14] This is a diagram of the scintillator 110 as seen from the direction of arrow AR1 in Figure 13. [Figure 15] (a) A diagram showing the magnitude of the output of the photodetector when light is emitted from segment (C), and (b) A diagram showing the magnitude of the output of the photodetector when light is emitted from segment (G). [Figure 16] This is a histogram summarizing the calculation results of DOI information based on the photodetector 120C with identification number n=3. [Figure 17] This diagram illustrates the DOI distribution when Black Tape BT is attached to the center in the X direction, and the DOI distribution when Black Tape BT is attached to a position shifted to the right of the center in the X direction. [Figure 18] This is an example of a flood map. [Figure 19] This is an example flowchart for determining the position in the Z direction. [Figure 20]This figure shows the frequency distribution (flood map) of gamma-ray events in two dimensions. [Figure 21] (a) An example of a scintillator 10 having a reflective material, a light-absorbing material (e.g., black tape), or a rough surface in the area indicated by symbol B1; (b) An example of a scintillator 10 having a reflective member symbol B1 on the upper surface (or side surface, etc.) of the scintillator 10. [Modes for carrying out the invention]

[0027] <Embodiment 1> Hereinafter, a radiation detector 1, which is Embodiment 1 of this disclosure, will be described with reference to the attached drawings. In each figure, corresponding components are denoted by the same reference numerals, and redundant explanations are omitted.

[0028] Figure 1 is a schematic diagram of the radiation detector 1 of Embodiment 1.

[0029] Radiation detector 1 is a DOI (Depth of Interaction) detector that identifies the location (depth direction) where high-energy gamma rays (annihilation radiation) incident into the scintillator 10 interact within the scintillator 10 and generate scintillation light.

[0030] As shown in Figure 1, the radiation detector 1 comprises a plurality of scintillators 10 and a photodetection unit 20. The plurality of scintillators 10 are arranged in a matrix in the XY direction. The scintillators 10 are covered with reflective members 17 to prevent scintillation light from passing between adjacent scintillators 10.

[0031] Figure 2 is a perspective view of the scintillator 10 and a portion of the light detection unit 20, extracted from Figure 1. For the sake of explanation, the reflective member 17 is omitted in Figure 2. For the sake of explanation, the X, Y, and Z axes are defined as shown in Figure 2. The X axis extends horizontally in Figure 2. The Z axis extends vertically in Figure 2. The Y axis extends perpendicular to the XZ plane.

[0032] As shown in Figure 2, the scintillator 10 comprises a scintillator array 12 including first scintillator blocks 11A and 11B arranged in parallel to each other in the first layer, and a second scintillator block 13 arranged in the second layer, straddling the first scintillator blocks 11A and 11B respectively. The material of the scintillator 10 is, for example, Bi4Ge3O 12 (BGO), Ce-doped Lu2SiO5(LSO), Lu2(1-X)Y2XSiO5(LYSO), Gd2SiO5(GSO), Pr-doped LuAG(Lu3Al5O 12 ), Ce-doped LaBr3 (LaBr3), Ce-doped LaCl3 (LaCl3), or Ce-doped Lu 0.7 Y 0.3 These are crystals (crystal masses) of AlO3 (LuYAP), Lutetium Fine Silicate (LFS), etc.

[0033] A reflective member 40 is placed between adjacent first scintillator blocks 11A and 11B, primarily to prevent scintillation light from traveling back and forth between the adjacent first scintillator blocks 11A and 11B. The reflective member 40 is, for example, an ESR (Enhanced Specular Reflector Film) reflective material.

[0034] First, let's describe the first scintillator blocks 11A and 11B. Since the first scintillator blocks 11A and 11B have similar configurations, we will describe the first scintillator block 11A as a representative example.

[0035] The first scintillator block 11A is a rectangular prism-shaped scintillator block including a pair of faces parallel to the XY plane, a pair of faces parallel to the XZ plane, and a pair of faces parallel to the YZ plane. The first scintillator block 11A may also be a polygonal prism shape other than a rectangular prism. All surfaces of the first scintillator block 11A are polished flat. This polishing may be mechanical or chemical. Note that each surface of the first scintillator block 11A is not limited to a mirror surface. That is, as long as the necessary amount of scintillation light for the photodetectors 20A and 20B is incident on them, each surface of the first scintillator block 11A may be a diffuse reflecting surface, an absorbing surface, a translucent surface, or any combination thereof.

[0036] The first scintillator blocks 11A and 11B are arranged adjacent to each other in the X direction with their respective sides (planes parallel to the YZ plane) facing each other. In this arrangement, when the first scintillator blocks 11A and 11B are projected onto the YZ plane, their respective outlines coincide on the YZ plane.

[0037] Next, we will describe the second scintillator block 13.

[0038] The second scintillator block 13 is a rectangular prism-shaped scintillator block including a pair of faces parallel to the XY plane, a pair of faces parallel to the XZ plane, and a pair of faces parallel to the YZ plane. The second scintillator block 13 may be a polygonal prism shape other than a rectangular prism. The X-direction length L1 of the second scintillator block 13 is twice the X-direction length of the first scintillator block 11A plus the X-direction thickness of the reflective member 40. On the other hand, the Y-direction length L2 and Z-direction length L3 of the second scintillator block 13 are the same as the Y-direction length and Z-direction length of the first scintillator block 11A. The Z-direction length (scintillator height) of the second scintillator block 13 may differ from that of the first scintillator block 11A. All surfaces of the second scintillator block 13 are polished flat. This polishing may be mechanical or chemical. Note that the surfaces of the second scintillator block 13 are not limited to mirror surfaces. In other words, as long as the necessary amount of scintillation light is incident on the photodetectors 20A and 20B, each surface of the second scintillator block 13 may be a diffuse reflecting surface, an absorbing surface, a semi-transparent surface, or any combination thereof.

[0039] The scintillator array 12 (first scintillator blocks 11A and 11B) and the second scintillator block 13 are arranged adjacent to each other in the Z direction, with the surfaces of the first scintillator blocks 11A and 11B parallel to the XY plane (upper surface in Figure 2) and the surface of the second scintillator block 13 parallel to the XY plane (lower surface in Figure 2) facing each other. In this arrangement, the scintillator array 12 and the second scintillator block 13 are arranged such that when projected onto the XY plane, their respective outlines coincide on the XY plane.

[0040] The first scintillator block 11A and the second scintillator block 13 are bonded together by an optical adhesive layer 14A provided between the surface of the first scintillator block 11A parallel to the XY plane (upper surface in Figure 2) and the surface of the second scintillator block 13 parallel to the XY plane (lower surface in Figure 2). Similarly, the first scintillator block 11B and the second scintillator block 13 are bonded together by an optical adhesive layer 14B provided between the surface of the first scintillator block 11B parallel to the XY plane (upper surface in Figure 2) and the surface of the second scintillator block 13 parallel to the XY plane (lower surface in Figure 2). The optical adhesive layers 14A and 14B are examples of the first optical discontinuity of this disclosure.

[0041] Hereinafter, the first scintillator blocks 11A and 11B may be referred to as segments (1) and (4), respectively. Also, the portion of the second scintillator block 13 directly above the first scintillator block 11A and the portion of the second scintillator block 13 directly above the first scintillator block 11B may be referred to as segments (2) and (3), respectively. The first scintillator block 11A and the portion of the second scintillator block 13 directly above the first scintillator block 11A are examples of the scintillator portion of this disclosure. Similarly, the first scintillator block 11B and the portion of the second scintillator block 13 directly above the first scintillator block 11B are also examples of the scintillator portion of this disclosure.

[0042] Within the scintillator 10 configured as described above, some of the scintillation light La (see Figure 1) generated in any of segments (1) to (4) propagates to one end face 15 (lower surface in Figure 2) of the first scintillator block 11A that is parallel to the XY plane, and is incident on a photodetector 20A that is optically connected to that end face 15. Similarly, some of the other scintillation light Lb generated within segments (1) to (4) propagates to the other end face 16 (lower surface in Figure 2) of the first scintillator block 11B that is parallel to the XY plane, and is incident on a photodetector 20B that is optically connected to that other end face 16. The photodetectors 20A and 20B each output an electrical signal corresponding to the light (photons) incident on them.

[0043] Next, we will explain how to identify the segment from which scintillation light was generated.

[0044] First, as shown in Figure 2, a radiation source 50 (for example, a disk source using the radioactive isotope sodium 22) that emits radiation in a 360-degree direction is placed directly facing the scintillator 10. For each time scintillation light is generated over a certain period (approximately 3 minutes), DOI information is calculated using the following equation 1 and stored in a memory device (not shown).

[0045]

number

[0046] Figure 3 is a histogram (DOI separation characteristic histogram) summarizing the calculation results of DOI information. In Figure 3, the vertical axis represents the number of event occurrences, and the horizontal axis represents the DOI information.

[0047] Referring to FIG. 3, it can be seen that valleys V1, V2, and V3 exist between segment (1) and segment (2), between segment (2) and segment (3), and between segment (3) and segment (4), respectively. In FIG. 3, reference signs DOI1, DOI2, and DOI3 respectively represent DOI information corresponding to valleys V1, V2, and V3.

[0048] The DOI information can be calculated using the above Equation 1 each time scintillation light is generated and outputs from the light receiving elements 20A and 20B are obtained. Then, by comparing the calculated DOI information with the DOI information DOI1 to DOI3 (threshold values), the light emission position in the Z direction can be determined, that is, the segment where the scintillation light is generated can be identified.

[0049] For example, if the calculated DOI information < DOI1, the segment where the scintillation light is generated can be identified as segment (1). Similarly, if DOI1 < calculated DOI information < DOI2, the segment where the scintillation light is generated can be identified as segment (2). Similarly, if DOI2 < calculated DOI information < DOI3, the segment where the scintillation light is generated can be identified as segment (3). Similarly, if DOI3 < calculated DOI information, the segment where the scintillation light is generated can be identified as segment (4).

[0050] The light detection unit 20 includes a first light receiving element 20A optically connected to the end face 15 of one first scintillator block 11A, and a second light receiving element 20B optically connected to the end face 16 of the other first scintillator block 11B. The light receiving elements 20A and 20B are, for example, semiconductor photodetectors using MPPC (Multi-Pixel Photon Counter). The MPPC is a photon counting device composed of a plurality of Geiger-mode APD pixels. The light receiving elements 20A and 20B output electrical signals corresponding to the light (photons) incident thereon. These electrical signals are input to the signal processing circuit 30 (see FIG. 5).

[0051] Next, a positron emission tomography (PET) system using the radiation detector 1 of this disclosure will be briefly described.

[0052] Figures 4 and 5 show an example of a positron emission tomography (POSTO) system 60 to which the radiation detector 1 of this disclosure is applied. As shown in Figures 4 and 5, the positron emission tomography system 60 includes a subject holding unit 62 that holds a subject 61 administered with a radioactive drug, a plurality of radiation detectors 1 arranged in a ring shape to detect radiation (annihilation gamma rays) emitted from the subject 61, and means (for example, a signal station circuit 30) that, based on the output of the radiation detectors 1 (photodetection unit 20), identify the segment (location) where scintillation light was generated, record the identified location in a memory (not shown), identify the location of the radiation emission site from the recorded location using mathematical methods, and display the identified location on a display device 63. At that time, the signal processing circuit 30 performs a process to identify the location (segment) where scintillation light was generated by comparing the DOI information calculated as described above with DOI information DOI1 to DOI3 (thresholds) stored in a memory device (not shown). The subject support unit 62 may be a bed on which the subject 61 lies, or a chair on which the subject 61 sits.

[0053] Next, we will explain the method for adjusting the DOI separation characteristics of radiation detector 1.

[0054] The DOI separation characteristic is represented by a histogram (hereinafter referred to as the DOI separation characteristic histogram) that summarizes the DOI information calculated from the outputs of the light-receiving elements 20A and 20B when the radiation detector 1 is uniformly irradiated with gamma rays and the above Equation 1, along with the calculation results. Figure 6(a) shows an example of the scintillator 10B in which the second scintillator block 13 is divided between segment (2) and segment (3) to form two scintillator blocks 13A and 13B, with an air layer interposed between one scintillator block 13A and the other scintillator block 13B. Figure 6(b) shows an example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in 360-degree directions is arranged, and the radiation detector 1 in Figure 6(a) is uniformly irradiated with radiation (gamma rays) for a certain period. Note that the irradiation time varies depending on the source position and source intensity. For example, when the distance from the top surface of the scintillator to the source is 5 cm and the dose is about 2 MBq, the irradiation time is about three minutes.

[0055] In this way, when the second layer is composed of two scintillator blocks 13A and 13B, and an optical discontinuity (here, an air layer) is provided between the two (see Figure 6(a)), as shown in Figure 6(b), the peak interval W2 (peak-to-peak interval) between the peaks respectively corresponding to segment (2) and segment (3) is sufficiently wide. If the peak interval W2 (peak-to-peak interval) respectively corresponding to segment (2) and segment (3) is clearly separated in this manner, there is an advantage that event discrimination becomes easy.

[0056] In contrast, when the second layer is composed of a single second scintillator block 13 as in the present embodiment (see Figure 2), as shown in Figure 3, the peak interval W1 between the peaks respectively corresponding to segment (2) and segment (3) becomes narrow. This peak interval W1 is desirably wider to facilitate event discrimination. This peak interval W1 can be widened by adopting the following DOI separation characteristic adjustment methods 1 and 2.

[0057] <DOI Separation Characteristic Adjustment Method 1> The inventors have discovered that the DOI separation characteristics of the radiation detector 1 can be adjusted by attaching black tape to the second scintillator block 13. This point will be explained below in comparison with a comparative example.

[0058] A comparative example is a radiation detector 1 (see Figure 2) in which black tape is not attached to the second scintillator block 13.

[0059] Figure 3 shows an example of a DOI separation characteristic histogram when radiation (gamma rays) is uniformly irradiated to the comparative example radiation detector 1 (see Figure 2) for a certain period (approximately 3 minutes). On the other hand, Figure 7(a) shows an example where black tape BT is attached to the upper surface of the second scintillator block 13, and Figure 7(b) shows an example of a DOI separation characteristic histogram when radiation (gamma rays) is uniformly irradiated to the radiation detector 1 in Figure 7(a) for a certain period (approximately 3 minutes) with a radiation source 50 that emits radiation in a 360-degree direction. As the black tape BT, industrial tape CP743 manufactured by Shurtape was used. Width W of the black tape BT BT (See Figure 7(a)) The thickness is approximately 1 mm. It is assumed that similar effects can be achieved using other types of black tape.

[0060] Referring to Figure 7(b), it can be seen that the interval W3 between peaks corresponding to segment (2) and segment (3) is wider than the interval W1 between peaks in the comparative example without black tape BT (see Figure 3), meaning that the DOI separation characteristics can be adjusted (improved) by applying black tape BT.

[0061] As described above, the DOI separation characteristics of the radiation detector 1 can be adjusted by attaching black tape BT to the second scintillator block 13. This is because attaching black tape BT, which is a light absorber, to the scintillator surface at the boundary position where the DOI separation characteristics are to be improved (in this case, the upper surface of the second scintillator block 13) changes the ratio of the amount of scintillation light incident on the photodetectors 20A and 20B.

[0062] The black tape BT can be attached to any scintillator surface at the boundary where separation characteristics are to be improved, and is not limited to the top surface of the second scintillator block 13 (see Figure 7(a)). For example, the black tape BT may be attached to the locations shown in Figures 8(a) to 8(d). Figure 8(a) shows an example where the black tape BT is attached to the top and side surfaces of the second scintillator block 13, Figure 8(b) shows an example where the black tape BT is attached to the bottom surface of the second scintillator block 13, Figure 8(c) shows an example where the black tape BT is attached to the bottom and side surfaces of the second scintillator block 13, and Figure 8(d) shows an example where the black tape BT is attached to the top, bottom, and side surfaces of the second scintillator block 13.

[0063] Furthermore, the placement of the black tape BT is not limited to the center of the second scintillator block 13 in the X direction (see Figures 7(a), 8(a) to 8(d)), but may be at a location offset from the center (see Figure 8(e)). Figure 8(e) shows an example where the black tape BT is placed at a location offset from the center. When the black tape BT is placed at the center in the X direction, the DOI distribution is generally symmetrical (the valley VA is at the center in the X direction), as shown on the left side of Figure 17. In contrast, when the black tape BT is placed at a position shifted to the right of the center in the X direction, the DOI distribution is asymmetrical (the valley VA is at a position shifted to the right of the center in the X direction), as shown on the right side of Figure 17. Figure 17 is an illustrative diagram of the DOI distribution when the black tape BT is placed at the center in the X direction and when the black tape BT is placed at a position shifted to the right of the center in the X direction.

[0064] Furthermore, other light-absorbing materials, such as black paint, may be used instead of black tape BT. The locations where other light-absorbing materials (e.g., black paint) are applied may be the same as the locations where black tape BT is applied. Note that black tape BT and black paint are examples of structures in which the spacing between peaks in the multi-peaked DOI separation characteristic histogram (see Figure 7(b)) is wider compared to when black tape BT and black paint are not applied.

[0065] <Method 2 for Adjusting DOI Separation Characteristics> The present inventors have found that the DOI separation characteristics of the radiation detector 1 can be adjusted by providing a notch portion in place of the black tape in the second scintillator block 13. This point will be described below.

[0066] FIGS. 9(a) and 9(b) are examples in which a notch portion NT is used in place of the black tape BT.

[0067] As shown in FIGS. 9(a) and 9(b), the notch portion NT may be used in place of the black tape BT. The width W of the notch portion NT NT (see FIG. 9(a)) is about 1 mm. The position where the notch portion NT is provided may be the upper surface or the lower surface of the scintillator at the boundary position where the separation characteristics are desired to be improved. FIG. 9(a) is an example in which the notch portion NT is provided on the upper surface of the second scintillator block 13. FIG. 9(b) is an example in which the notch portion NT is provided on the lower surface of the second scintillator block 13. Note that the notch depth D1 (see FIG. 9(a)) is preferably shallow so that the notch portion NT functions as a scattering surface and prevents sensitivity loss. On the other hand, if the separation is insufficient, adjustment can be performed by deepening the notch.

[0068] As described above, the DOI separation characteristics of the radiation detector 1 can be adjusted by providing the notch portion in the second scintillator block 13 in place of the black tape. This is because by providing the notch portion NT functioning as a scattering surface on the upper surface or the lower surface of the scintillator at the boundary position where the DOI separation characteristics are desired to be improved, the ratio of the amounts of scintillation light incident on the light receiving elements 20A and 20B changes, similarly to the above-described method 1 for adjusting DOI separation characteristics.

[0069] The position where the notch portion NT is provided is not limited to the center of the second scintillator block 13 in the X direction (see Fig. 9(a) and Fig. 9(b)), and may be a position displaced from the center. Note that a specular reflector (for example, ESR) or a diffuse reflector (for example, Teflon tape, barium sulfate paint) may be inserted into the notch portion NT. This can be expected to enhance the effect of varying the light throughput compared to the case where only the notch portion NT is provided.

[0070] Further, instead of the notch portion NT (notch processing), another light scattering material (light scattering processing), for example, a rough surface (rough surface processing) functioning as a light scattering surface, or a laser-processed surface functioning as a light scattering surface may be used. The position where the other light scattering member is provided may be the same as the position where the notch portion NT is provided. Note that the notch portion, the rough surface, and the laser-processed surface are examples of the structure of the present disclosure, that is, a structure in which the interval between peaks in the multimodal DOI separation characteristic histogram is wider than in the case where the notch portion NT, the rough surface, and the laser-processed surface are not provided.

[0071] <Method 3 for Adjusting DOI Separation Characteristics> The present inventors have found that the DOI separation characteristics of the radiation detector 1 can be adjusted by providing a diffuse reflector in the second scintillator block 13 in place of the black tape and the notch portion. This point will be described below.

[0072] Fig. 10(a) shows an example in which the second scintillator block 13 is divided between segment (2) and segment (3) to form two scintillator blocks 13A and 13B, an air layer is formed between one scintillator block 13A and the other scintillator block 13B, and the top surface and side surfaces of the second scintillator block 13 are covered with a reflecting member 40 (for example, ESR) which is a specular reflector. Fig. 10(b) shows an example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in 360-degree directions is arranged, and the radiation detector 1 in Fig. 10(a) is uniformly irradiated with radiation (gamma rays) for a certain period (about 3 minutes).

[0073] Figure 10(c) shows an example in which the second scintillator block 13 is divided between segment (2) and segment (3) to form two scintillator blocks 13A and 13B, with an air layer between one scintillator block 13A and the other scintillator block 13B, and a portion of the upper surface of the second scintillator block 13 (the upper surface of scintillator block 13A) is covered with a diffuse reflector 19 (Teflon (registered trademark; the same applies hereinafter)). The other portion of the upper surface of the second scintillator block 13 (the upper surface of scintillator block 13B) is covered with a reflective member 40 (e.g., ESR). Figure 10(d) shows an example of a DOI separation characteristic histogram when a radiation source 50 that emits radiation in a 360-degree direction is placed and radiation (gamma rays) is uniformly irradiated onto the radiation detector 1 in Figure 10(c) for a certain period (approximately 3 minutes).

[0074] Referring to Figure 10(d), it can be seen that the spacing W5 of the peaks corresponding to segment (2) and segment (3) is narrower (the amount of light flow increases) compared to the spacing W4 of the peaks in the example without the diffuse reflector 19 (Teflon) (see Figure 10(b)), meaning that the DOI separation characteristics can be adjusted.

[0075] As described above, the DOI separation characteristics of the radiation detector 1 can be adjusted by providing a diffuse reflector in place of the black tape and notches in the second scintillator block 13. This is because the diffuse reflector 19 (Teflon) reduces the scintillation light trapped within the scintillator 10, promoting its incidence to the photodetectors 20A and 20B, thereby increasing the amount of light detected by the photodetectors 20A and 20B. The diffuse reflector 19 (Teflon) is an example of a structure in which the spacing between peaks in the multi-peaked DOI separation characteristic histogram (see Figure 10(d)) becomes narrower compared to the case where the diffuse reflector 19 (Teflon) is not provided.

[0076] Furthermore, a diffuse reflective surface (e.g., a rough surface, a diffuse reflective material) may be provided on the scintillator surface around the boundary of the U-shaped unit for light (scintillation light) to flow to the adjacent scintillator (the surface of the second scintillator block 13 of the second layer). In this case as well, light trapping is prevented and the amount of light flow is improved. As a result, the spacing between peaks in the multi-peaked DOI separation characteristic histogram (see Figure 10(d)) becomes narrower.

[0077] The above describes an example of applying DOI separation characteristic adjustment method 3 to scinturator 10B shown in Figure 10(c). However, it can be assumed that similar results will be obtained if DOI separation characteristic adjustment method 3 is applied to scinturator 10 shown in Figure 2.

[0078] Figure 21(a) shows an example of a scintillator 10 in which a reflective material, a light-absorbing material (e.g., black tape), or a rough surface is provided in the area indicated by the symbol B1.

[0079] As shown in Figure 21(a), instead of black tape on the second scintillator block 13 and notches, a reflective material, a light-absorbing material (e.g., black tape), or a rough surface may be provided at the boundary BD (within the light flow path) within the scintillator 10, for example, at the first optical discontinuity (e.g., optical adhesive layers 14A, 14B). In Figure 21(a), the symbol B1 represents the area where the reflective material, light-absorbing material (e.g., black tape), or rough surface is provided. This restricts the flow of light (scintillation light) within the scintillator 10, thereby allowing the DOI separation characteristics of the radiation detector 1 to be adjusted.

[0080] Thus, when there is a structure within the light path, the flow of light (scintillation light) within the scintillator 10 is restricted, and the spacing between peaks (see, for example, the symbol W3 in Figure 7(b)) widens. Examples of such structures include notches, laser-processed walls, rough surfaces provided on the boundary BD within the scintillator 10, reflective materials, and notches.

[0081] Figure 21(b) shows an example of a scintillator 10 in which a reflective member Ref. B1 is provided on the upper surface (or side surface, etc.) of the scintillator 10.

[0082] As shown in Figure 21(b), instead of black tape and notches on the second scintillator block 13, a reflective member Ref (e.g., a diffuse reflector, a rough surface as a diffuse reflecting surface) may be provided on the upper surface (or side, etc.) of the scintillator 10. This causes the light trapped in the scintillator 10 (scintillation light) to be diffusely reflected by the reflective member Ref, disrupting the path pattern of the trapped light and increasing the amount of light (scintillation light) flowing through the scintillator 10, thereby adjusting the DOI separation characteristics of the radiation detector 1. The above describes an example of applying DOI separation characteristic adjustment methods 1 to 3 to the scintillator 10 shown in Figure 2, but it is not limited to this. That is, DOI separation characteristic adjustment methods 1 to 3 can be applied to any scintillator as long as it is configured to allow light to flow between at least two scintillator sections arranged in parallel and between one end of each of the at least two scintillator sections.

[0083] For example, the DOI separation characteristics adjustment methods 1 to 3 shown in Figures 11(a) to 11(c) may be applied to scintillators other than the scintillator 10 shown in Figure 2. Figure 11(a) is an example of a scintillator 10B with a similar configuration to the scintillator shown in Figure 10(a). Figure 11(b) is an example of a U-shaped scintillator 10C constructed by forming a notch N in one scintillator block. Figure 11(c) is an example of a scintillator similar to the scintillator described in Patent Document 1, that is, a U-shaped scintillator 10D having two scintillator sections 10D1 and 10D2 arranged in parallel with each other, and configured so that light (scintillation light) can flow between one end of each of these two scintillator sections 10D1 and 10D2. Each scintillator section 10D1 and 10D2 is divided into multiple segments by a modified region A1 formed by laser irradiation.

[0084] As described above, according to this embodiment, the DOI separation characteristics of the radiation detector 1 can be adjusted by a structure that controls the amount of scintillation light flowing within the scintillator 10, such as the black tape BT, the notched portion NT, and the diffuse reflector 19 (Teflon).

[0085] Furthermore, according to this embodiment, since the scintillator 10 is composed of a first scintillator block 11A, 11B and a second scintillator block 13, which are separate from each other, and optical adhesive layers 14A, 14B (first optical discontinuity) provided between them, the laser irradiation modification region can be omitted (partially or entirely omitted). Figure 2 shows an example in which the modification region is completely omitted, and Figure 12 shows an example in which the modification region is partially omitted. As a result, compared to Patent Document 1, in which a laser irradiation modification region is formed in each scintillator, the manufacturing cost and manufacturing time of the scintillator 10 can be reduced.

[0086] Furthermore, according to this embodiment, since only one second scintillator block 13 is required for multiple first scintillator blocks 11A, 11B in the first layer, the number of scintillator blocks can be reduced. In addition, according to this embodiment, the polished surface of the scintillator blocks can also be reduced. As a result, cost reduction is possible by simplifying the assembly of scintillators 11A, 11B, and 13.

[0087] Furthermore, this embodiment has the advantage that calibration in the DOI direction, which was conventionally performed in scintillators that do not form a modified region by laser irradiation, is unnecessary.

[0088] Furthermore, according to this embodiment, each of the multiple first scintillator blocks 11A and 11B may be divided into multiple segments by at least one modified layer 18 (second optical discontinuity) (see Figure 12), and in this way, the generation of scintillation light can be detected in three or more layers.

[0089] Furthermore, according to this embodiment, the multiple first scintillator blocks 111A, 111B, 111C, and 111D may be arranged in a matrix in the first layer (see Figure 13). In this case, only one second scintillator block 113 is needed for the multiple first scintillator blocks 111A, 111B, 111C, and 111D in the first layer, thus reducing the number of scintillator blocks. The polished surface of the scintillator blocks can also be reduced. As a result, cost reduction is possible through simplification of scintillator assembly.

[0090] Next, I will explain some variations.

[0091] In the above embodiment, an example using a scintillator 10 in which two layers of scintillator blocks are arranged has been described, but the invention is not limited to this. Figure 12 is a perspective view of a modified scintillator 10A. For example, as shown in Figure 12, a scintillator 10A in which three or more layers of scintillator blocks are arranged may be constructed by forming a modified layer 18 by laser processing on each of the first scintillator blocks 11A and 11B. Also, although not shown, a scintillator in which three or more layers of scintillator blocks are arranged may be constructed by bonding another first scintillator block 11A or 11B to each of the first scintillator blocks 11A or 11B via an optical adhesive layer. Furthermore, in the above embodiment, an air layer may be used instead of the modified layer 18. The modified layer 18, the air layer, and the optical adhesive layer are examples of the second optical discontinuity in this disclosure. The above DOI separation characteristic adjustment methods 1 to 3 may also be applied to the modified scintillator 10A shown in Figure 12.

[0092] Next, we will describe a modified example, scintillator 110.

[0093] Figure 13 is a schematic perspective view of a radiation detector 2 using a modified scintillator 110.

[0094] As shown in Figure 13, the radiation detector 2 includes a scintillator 110 and a photodetection unit 120.

[0095] The scintillator 10 of the above embodiment had two first scintillator blocks 11A and 11B arranged in parallel with each other in the first layer (see Figure 2), whereas the scintillator 110 of this modified example has four first scintillator blocks 111A, 111B, 111C, and 111D arranged in parallel with each other in the first layer (see Figure 13). Furthermore, the scintillator 10 of the above embodiment had one second scintillator block 13 arranged in the second layer, straddling each of the two first scintillator blocks 11A and 11B (see Figure 2), whereas the scintillator 110 of this modified example has one second scintillator block 113 arranged in the second layer, straddling each of the four first scintillator blocks 111A, 111B, 111C, and 111D (see Figure 13).

[0096] The material of scintillator 110 is the same as that of scintillator 10, so its explanation is omitted.

[0097] Reflective members 140 are placed between adjacent first scintillator blocks 111A, 111B, 111C, and 111D to prevent scintillation light from traveling back and forth between them. The reflective members 140 are, for example, ESR (Enhanced Specular Reflector Film) reflective materials.

[0098] First, we will describe the first scintillator blocks 111A, 111B, 111C, and 111D. Since the first scintillator blocks 111A, 111B, 111C, and 111D have similar configurations, we will describe the first scintillator block 111A as a representative example.

[0099] The first scintillator block 111A is a rectangular prism-shaped scintillator block, similar to the first scintillator block 11A, and includes a pair of faces parallel to the XY plane, a pair of faces parallel to the XZ plane, and a pair of faces parallel to the YZ plane. The first scintillator block 111A may have a polygonal prism shape other than a rectangular prism. All surfaces of the first scintillator block 111A are polished flat. This polishing may be mechanical or chemical. The surfaces of the first scintillator block 111A are not limited to mirror surfaces. That is, as long as the scintillation light of the required intensity for the photodetectors 120A to 120D is incident on them, the surfaces of the first scintillator block 111A may be diffuse reflectors, absorbers, translucent surfaces, or any combination thereof.

[0100] The first scintillator blocks 111A, 111B, 111C, and 111D are arranged adjacent to each other in a matrix (2x2) in the X and Y directions, with their respective sides facing each other. In this arrangement, the first scintillator blocks 111A and 111B are positioned such that their outlines coincide when projected onto the YZ plane. The same applies to the first scintillator blocks 111C and 111D.

[0101] Next, we will describe the second scintillator block 113.

[0102] The second scintillator block 113, like the second scintillator block 13, is a rectangular prism-shaped scintillator block including a pair of faces parallel to the XY plane, a pair of faces parallel to the XZ plane, and a pair of faces parallel to the YZ plane. The second scintillator block 113 may have a polygonal prism shape other than a rectangular prism. The X-direction length L1 and Y-direction length L2 of the second scintillator block 113 are twice the X-direction length and Y-direction length of the first scintillator block 11A, and the Z-direction length L3 of the second scintillator block 113 is the same as the Z-direction length of the first scintillator block 11A. The Z-direction length (scintillator height) of the second scintillator block 113 may differ from that of the first scintillator block 11A. All surfaces of the second scintillator block 113 are polished flat. This polishing may be mechanical or chemical. The surfaces of the second scintillator block 113 are not limited to mirror finishes. In other words, as long as the necessary amount of scintillation light is incident on the photodetectors 120A to 120D, each surface of the second scintillator block 113 may be a diffuse reflecting surface, an absorbing surface, a semi-transparent surface, or any combination thereof.

[0103] The scintillator array 112 (first scintillator blocks 111A, 111B, 111C, 111D) and the second scintillator block 113 are arranged adjacent to each other in the Z direction, with the surfaces of the first scintillator blocks 111A, 111B, 111C, and 111D parallel to the XY plane (upper surfaces in Figure 13) and the surface of the second scintillator block 113 parallel to the XY plane (lower surfaces in Figure 13) facing each other. In this arrangement, the scintillator array 112 and the second scintillator block 113 are arranged such that when projected onto the XY plane, their respective outlines coincide on the XY plane.

[0104] The first scintillator block 111A and the second scintillator block 113 are bonded together by an optical adhesive layer 114A provided between the surface of the first scintillator block 111A parallel to the XY plane (upper surface in Figure 13) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 13). Similarly, the first scintillator block 111B and the second scintillator block 113 are bonded together by an optical adhesive layer 114B provided between the surface of the first scintillator block 111B parallel to the XY plane (upper surface in Figure 13) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 13). Similarly, the first scintillator block 111C and the second scintillator block 113 are bonded together by an optical adhesive layer 114C provided between the surface of the first scintillator block 111C parallel to the XY plane (upper surface in Figure 13) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 13). Similarly, the first scintillator block 111D and the second scintillator block 113 are bonded together by an optical adhesive layer 114D provided between the surface of the first scintillator block 111D parallel to the XY plane (upper surface in Figure 13) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 13). Note that an air layer may be used instead of the optical adhesive layers 114A, 114B, 114C, and 114D. The optical adhesive layers 114A, 114B, 114C, 114D and the air layer are examples of the first optical discontinuity of this disclosure. The above DOI separation characteristics adjustment methods 1 to 3 may also be applied to the modified scintillator 110 shown in Figure 13.

[0105] Hereinafter, the first scintillator blocks 111A, 111B, 111C, and 111D may be referred to as segments (A), (B), (C), and (D), respectively. Additionally, the portion of the second scintillator block 113 directly above the first scintillator block 111A, the portion of the second scintillator block 113 directly above the first scintillator block 111B, the portion of the second scintillator block 113 directly above the first scintillator block 111C, and the portion of the second scintillator block 113 directly above the first scintillator block 111D may be referred to as segments (E), (F), (G), and (H), respectively.

[0106] Within the scintillator 110 configured as described above, that is, in any of segments (A) to (H), scintillation light propagates to the end faces (lower faces in Figure 13) parallel to the XY plane of each of the first scintillator blocks 111A, 111B, 111C, and 111D, and is incident on the photodetectors 120A to 120D that are optically connected to these end faces. The photodetectors 120A to 120D output an electrical signal corresponding to the light (photons) incident on them.

[0107] Next, we will explain how to identify the segment from which scintillation light was generated. The segment from which scintillation light was generated is identified by its position in the XY direction and its position in the Z direction.

[0108] First, let's explain how to determine the position in the X and Y directions.

[0109] Figure 14 shows the scintillator 110 as viewed from the direction of arrow AR1 in Figure 13.

[0110] First, calibration data for discriminating gamma-ray emission positions in two dimensions is acquired. Calibration data refers to reference data that associates known gamma-ray emission positions with the outputs of photodetectors 120A to 120D in order to accurately identify gamma-ray emission positions in two dimensions (XY direction). This calibration data can be acquired, for example, by known methods using a collimated radiation source (for example, a radiation source using the radioactive isotope sodium-22) and a reference radiation detector.

[0111] Next, a flood map is created from the outputs of the photodetectors 120A to 120D to set a threshold for two-dimensional position discrimination. The flood map is data that is calculated by determining the output ratio of the photodetectors 120A to 120D detected for each event and representing it as a frequency distribution in two dimensions (XY direction). This flood map can be calculated using a known method based on the outputs of the photodetectors 120A to 120D. By comparing this flood map with the outputs of the photodetectors 120A to 120D, it is possible to discriminate in two dimensions the segment in which the target event occurred (for example, "segment (A) or (E)" or "segment (D) or (H)").

[0112] Figure 18 is an example of a flood map. In Figure 18, the codes Energy0 to 3 represent the output of the photodetectors 120A to 120D.

[0113] A flood map can be created as follows:

[0114] First, the sum of the outputs in the Y and X directions (sum_Vx, sum_h) from the four photodetectors 120A to 120D is calculated using equations 2 and 3 below.

[0115]

number

[0116]

number

[0117] Next, we will explain how to determine the position in the Z direction.

[0118] Figure 19 is an example flowchart of a method for determining the position in the Z direction.

[0119] The following explanation assumes that the flood map and its thresholds have been created in advance and stored in a memory unit (not shown). Steps S10 to S13 below are executed for each event.

[0120] First, using equations 2-5 above, the emission position in the two-dimensional direction (sum_v xg , sum_h yg Calculate (Step S10).

[0121] Next, the reference Energy (here, Energy) and the emission position in the two-dimensional direction (here, "segment (D) or (H)") are determined by comparing the output of the photodetectors 120A to 120D with the threshold values ​​of the flood map (Thx, Thy shown in Figure 20). Figure 20 is a diagram showing the frequency distribution (flood map) of gamma-ray events in the two-dimensional direction. In Figure 20, the symbols A1 to A4 each represent regions where gamma-ray events are concentrated (white regions in Figure 20). The threshold values ​​Thx and Thy in Figure 20 may be manually set by visually inspecting the flood map (see, for example, Figure 20), automatically set to an intermediate position between adjacent regions A1 to A4 in the two-dimensional direction, or set by other methods.

[0122] Next, the DOI information is calculated using the following equation 6 (step S12).

[0123]

number

[0124] Figure 15(a) is a diagram showing the magnitude of the output of the light receiving elements when scintillation light is generated in the segment (C), and Figure 15(b) is a diagram showing the magnitude of the output of the light receiving elements when scintillation light is generated in the segment (G). Each circle in Figure 15(a) represents the magnitude of the output of the light receiving elements 120A to 120D when scintillation light is generated in the segment (C). Similarly, each circle in Figure 15(b) represents the magnitude of the output of the light receiving elements 120A to 120D when scintillation light is generated in the segment (G). As described above, the ratio of the outputs of the light receiving elements differs depending on the segment (position in the Z direction) where the scintillation light is generated. As a result, a histogram summarizing the calculation results of the DOI information based on the light receiving element 120C with the identification number n=3 is, for example, as shown in Figure 16. Figure 16 is a histogram summarizing the calculation results of the DOI information based on the light receiving element 120C with the identification number n=3. In Figure 16, the vertical axis represents the number of event occurrences, and the horizontal axis represents the DOI information.

[0125] Referring to Figure 16, it can be seen that a valley Va exists between the segment (C) and the segment (G). In Figure 16, the reference sign DOIa represents the DOI information based on the light receiving element 120C with the identification number n=3 corresponding to the valley Va.

[0126] DOI information can be calculated using Equation 6 above each time scintillation light is generated in the segment (C) or the segment (G) and outputs are produced from the light receiving elements 120A to 120D. Then, by comparing the calculated DOI information with a threshold value of the DOI information (DOI information DOIa), the light emission position in the Z direction can be determined (step S13), that is, the segment where the scintillation light is generated can be identified.

[0127] For example, when the calculated DOI information is less than DOIa, the segment where the scintillation light is generated can be identified as the segment (C). Similarly, when DOIa is less than the calculated DOI information, the segment where the scintillation light is generated can be identified as the segment (G).

[0128] In the same manner as described above, even when scintillation light is generated in the segment (A) or the segment (E), the segment (B) or the segment (F), or the segment (D) or the segment (H), the segment where the scintillation light is generated can be identified.

[0129] This modified example can also achieve the same effects as the above-described embodiment. Note that in this modified example, an example using a combination of 2×2 first scintillator blocks and light receiving elements has been described, but the present invention is not limited to this. That is, as long as the first scintillator blocks and the light receiving elements are in a one-to-one correspondence, a combination of 3×3, 4×4, 6×12, or other numbers of first scintillator blocks and light receiving elements may be used.

[0130] All numerical values shown in the above-described embodiment are merely examples, and it goes without saying that appropriate different numerical values can be used.

[0131] The above-described embodiment is merely an example in all respects. The present disclosure should not be construed as being limited by the description of the above-described embodiment. The present disclosure can be implemented in various other forms without departing from the spirit or main features thereof. [Description of Reference Signs]

[0132] 1, 2... Radiation detectors 10, 10A... Scintillator 11A, 11B...First scintillator block 12... Scintillator array 13…Second scintillator block 14A, 14B...Optical adhesive layer 15, 16...end face 17…Reflective material 18…Modified layer 20…Light detection unit 20A, 20B... Photodetector 30... Signal processing circuits 40…Reflective material 50…Radiation source 60…Positron Emission Fault Device 61…Subject 62...Subject holding part 63…Information Processing Devices 64…Display device 110... Scintillator 111A, 111B, 111C, 111D... First scintillator block 112...Scintillator array 113...Second scintillator block 114A, 114B, 114C, 114D...Optical adhesive layer 120... Light detection unit 120A, 120B, 120C, 120D… Photodetector 140…Reflective material 150…Radiation source

[0133] (1)~(4), (A)~(H)...Segments DOI1~DOI3, DOIa... DOI information La, Lb... Scintillation light V1~V3, Va... Valley n...Identification number

Claims

1. A scintillator comprising at least two scintillator sections arranged in parallel with each other, and a scintillator configured to allow light to flow between one end of each of the at least two scintillator sections, A photodetector unit optically connected to the other end of each of the at least two scintillator sections, Equipped with, The scintillator is a radiation detector that includes a structure for controlling the amount of scintillation light flowing through the scintillator.

2. The radiation detector according to claim 1, wherein the structure is such that the spacing between peaks in a multi-peaked DOI separation characteristic histogram is wider than in the case where the structure is not provided.

3. The radiation detector according to claim 2, wherein the structure is a light-absorbing material that absorbs at least a portion of the scintillation light generated in the scintillator.

4. The radiation detector according to claim 3, wherein the light-absorbing material is black tape or black paint.

5. The radiation detector according to claim 2, wherein the structure is a light scattering material that scatters at least a portion of the scintillation light generated in the scintillator.

6. The radiation detector according to claim 5, wherein the light scattering material is a notch formed in the scintillator, a rough surface that functions as a light scattering surface, or a laser-processed surface that functions as a light scattering surface.

7. The radiation detector according to claim 1, wherein the structure is such that the spacing between peaks in a multi-peaked DOI separation characteristic histogram is narrower compared to the case where the structure is not provided.

8. The radiation detector according to claim 7, wherein the structure is a diffuse reflector that diffusely reflects scintillation light generated in the scintillator.

9. The system comprises: a subject holding unit for holding a subject administered a radioactive drug; a ring-shaped radiation detector for detecting radiation emitted from the subject; and means for identifying the location where scintillation light is generated based on the output of the radiation detector, recording the identified location, using mathematical methods to identify the location of the radiation emission site from the recorded location, and displaying the identified location on a display device. The aforementioned radiation detector is A scintillator comprising at least two scintillator sections arranged in parallel with each other, and a scintillator configured to allow light to flow between one end of each of the at least two scintillator sections, A photodetector unit optically connected to the other end of each of the at least two scintillator sections, Equipped with, The scintillator is a positron emission tomography device that includes a structure for controlling the amount of scintillation light flowing within the scintillator.

Images