Radiation detector and positron emission tomography device

Abstract

The objective is to provide a radiation detector or the like that can omit (partially or completely) the modification region by laser irradiation. [Solution] A radiation detector 1 comprises a scintillator array 12 including a plurality of first scintillator blocks 11A, 11B arranged in parallel with each other in a first layer, a single second scintillator block 13 arranged in a second layer straddling each of the plurality of first scintillator blocks, a reflective member 40 arranged between adjacent first scintillator blocks, first optical discontinuities 14A, 14B provided between each of the plurality of first scintillator blocks and the second scintillator block, and a photodetection unit 20 optically connected to the end face 15 of one of the first scintillator blocks and the end face 16 of the other first scintillator block.

Description

Technical Field

[0001] The present disclosure relates to a radiation detector and a positron emission tomography apparatus.

Background Art

[0002] A radiation detector is known that includes a scintillator (U-shaped scintillator) which has two scintillator portions arranged in parallel to each other, and is configured such that light (scintillation light) can circulate between one end portion of each of the two scintillator portions (see, for example, Patent Document 1). The scintillator portion of Patent Document 1 is partitioned into a plurality of segments by modified regions (light scattering portions with light transmittance varying with incident angle) formed by laser irradiation. By forming these modified regions, the ratio of scintillation light reaching both end portions of the scintillator varies for each segment where scintillation light is generated. Therefore, by performing a predetermined calculation based on the outputs of light receiving elements optically connected to the both end portions, the segment where the scintillation light is generated can be identified.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] However, since a positron emission tomography apparatus (PET (Positron Emission Tomography) apparatus) to which a radiation detector is applied generally uses an extremely large number of scintillators, there is a problem that forming modified regions by laser irradiation on each scintillator requires enormous man-hours and time. For example, in the case where one processor performs laser processing one by one on scintillators (for example, 7000 pieces) used in a small-sized system, it takes 140 days at a processing rate of 50 pieces per day. This number of days varies greatly depending on the processing environment.

[0005] This disclosure is made to solve these problems and aims to provide a radiation detector and a positron emission tomography system that can omit (partially or completely omit) the laser irradiation modification region. [Means for solving the problem]

[0006] A radiation detector according to a first aspect of the embodiment includes a scintillator array including a plurality of first scintillator blocks arranged in parallel with each other in a first layer, a single second scintillator block arranged in a second layer straddling each of the plurality of first scintillator blocks, a reflective member arranged between adjacent first scintillator blocks, a first optical discontinuity provided between each of the plurality of first scintillator blocks and the second scintillator block, and a photodetection unit optically connected to the end face of one of the first scintillator blocks and the end face of the other first scintillator block.

[0007] Alternatively, a positron emission tomography apparatus according to a second aspect of the embodiment comprises: a subject holding unit for holding a subject administered a radioactive drug; a radiation detector arranged in a ring shape 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 indicating the location of the emission site; and a display device for displaying the image, wherein the radiation detector comprises: a scintillator array including a plurality of first scintillator blocks arranged in parallel with each other in a first layer; a second scintillator block arranged in a second layer straddling each of the plurality of first scintillator blocks; a reflective member arranged between adjacent first scintillator blocks; a first optical discontinuity provided between each of the plurality of first scintillator blocks and the second scintillator block; and a photodetection unit optically connected to the end face of one of the first scintillator blocks and the end face of the other first scintillator block.

[0008] According to the first or second aspect described above, since the scintillator is composed of a first scintillator block and a second scintillator block that are separate from each other, and a first optical discontinuity provided between them, the laser irradiation modification region can be omitted (partially or entirely 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 can be reduced.

[0009] Furthermore, according to the first or second aspect described above, since only one second scintillator block is needed for multiple first scintillator blocks in the first layer, the number of scintillator blocks can be reduced. In addition, the polished surface area of ​​the scintillator blocks can also be reduced. As a result, cost reduction is possible through simplification of scintillator assembly.

[0010] Furthermore, according to the first or second aspect described above, there is also the advantage that calibration in the DOI direction (for determining the gamma-ray interaction position), which was conventionally performed in scintillators that do not form a modified region by laser irradiation, is unnecessary.

[0011] Furthermore, in the first or second aspect described above, it is also preferable that each of the plurality of first scintillator blocks is divided into multiple segments by at least one second optical discontinuity. In this way, the location of scintillation light generation can be discriminated using three or more layers.

[0012] Furthermore, in the first or second aspect described above, it is also preferable that the plurality of first scintillator blocks are arranged in a matrix in the first layer. In this way, only one second scintillator block is needed for the plurality of first scintillator blocks in the first layer, thus reducing the number of scintillator blocks. In addition, the polished surface of the scintillator blocks can also be reduced. As a result, cost reduction is possible through simplification of scintillator assembly.

[0013] Furthermore, in the first or second aspect described above, the first optical discontinuity may preferably be an optical adhesive layer or an air layer. This is an example of the first optical discontinuity. The first optical discontinuity may also be something other than an optical adhesive layer or an air layer.

[0014] Furthermore, in the first or second aspect described above, the second optical discontinuity may also be a modified layer, an optical adhesive layer, or an air layer formed by laser irradiation of the first scintillator block. This is an example of the second optical discontinuity. The second optical discontinuity may also be something other than a modified layer, an air layer, or an optical adhesive layer.

[0015] Furthermore, in the first or second aspect described above, the photodetector unit may also preferably include at least one first photodetector optically connected to the end face of one of the first scintillator blocks, and at least one second photodetector optically connected to the end face of the other first scintillator block. That is, one or more first photodetectors may be optically connected to the end face of one of the first scintillator blocks. Similarly, one or more first photodetectors may be optically connected to the end face of the other first scintillator block.

[0016] The radiation detector of the embodiment is a [1] "radiation detector comprising: a scintillator array including a plurality of first scintillator blocks arranged in parallel with each other in a first layer; a single second scintillator block arranged in a second layer straddling each of the plurality of first scintillator blocks; a reflective member arranged between adjacent first scintillator blocks; a first optical discontinuity provided between each of the plurality of first scintillator blocks and the second scintillator block; and a photodetection unit optically connected to the end face of the first scintillator block and the end face of the second scintillator block."

[0017] The radiation detector of the embodiment may be [2] "the radiation detector according to [1] above, wherein each of the plurality of first scintillator blocks is partitioned into a plurality of segments by at least one second optical discontinuity."

[0018] The radiation detector of the embodiment may be [3] "the radiation detector described in [1] above, wherein the plurality of scintillator blocks are arranged in a matrix in the first layer."

[0019] The radiation detector of the embodiment may be [4] "the radiation detector described in [1] above, wherein the first optical discontinuity is an optical adhesive layer or an air layer."

[0020] The radiation detector of the embodiment may be [5] "the radiation detector according to [2] above, wherein the second optical discontinuity is a modified layer, an air layer, or an optical adhesive layer formed by laser irradiation of the first scintillator block."

[0021] The radiation detector of the embodiment may be [6] "the radiation detector according to [1] to [5] above, wherein the photodetector unit includes at least one first photodetector optically connected to the end face of the first scintillator block and at least one second photodetector optically connected to the end face of the second scintillator block."

[0022] The positron emission tomography apparatus according to the embodiment may be [7] "a positron emission tomography apparatus comprising: a subject holding unit configured to hold a subject to which a radiopharmaceutical has been 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 configured to display the image, wherein the radiation detectors each comprise: a scintillator array including a plurality of first scintillator blocks arranged in parallel with each other in a first layer; one second scintillator block arranged in a second layer so as to straddle each of the plurality of first scintillator blocks; a reflective member arranged between the adjacent first scintillator blocks; a first optical discontinuity provided between each of the plurality of first scintillator blocks and the second scintillator block; and a photodetection unit optically connected to an end face of the first scintillator block and an end face of the second scintillator block". [Effects of the Invention]

[0023] According to the present disclosure, it is possible to provide a radiation detector and a positron emission tomography apparatus in which a modified region formed by laser irradiation can be omitted (partially or entirely omitted). [Brief Description of the Drawings]

[0024] [Figure 1] FIG. 2 is a schematic configuration diagram of a radiation detector according to Embodiment 1. [Figure 2] FIG. 2 is a perspective view of a scintillator extracted from FIG. 1 and a part of a photodetection unit. [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 to which the radiation detector of the present disclosure is applied. [Figure 5] This is an example of a positron emission tomography apparatus to which the radiation detector of the present disclosure is applied. [Figure 6] FIG. 2 is a perspective view of a scintillator according to a modified example. [Figure 7] This is a schematic perspective view of a radiation detector 2 using a modified scintillator 110. [Figure 8] This is a diagram of the scintillator 110 as seen from the direction of arrow AR1 in Figure 7. [Figure 9] (a) A diagram showing the output magnitude of the photodetector when light is emitted from segment (C), and (b) A diagram showing the output magnitude of the photodetector when light is emitted from segment (G). [Figure 10] This is a histogram summarizing the calculation results of DOI information based on the photodetector 120C with identification number n=3. [Figure 11] This is an example of a flood map. [Figure 12] This is an example flowchart for determining the position in the Z direction. [Figure 13] This figure shows the frequency distribution (flood map) of gamma-ray events in two dimensions. [Modes for carrying out the invention]

[0025] <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.

[0026] Figure 1 is a schematic diagram of the radiation detector 1 of Embodiment 1.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Next, we will describe the second scintillator block 13.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Hereinafter, the first scintillator blocks 11A and 11B may be referred to as segments (1) and (4), respectively. Additionally, 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.

[0039] 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.

[0040] Next, we will explain how to identify the segment from which scintillation light was generated.

[0041] 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).

[0042]

number

[0043] Figure 3 is a 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.

[0044] Referring to Figure 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 Figure 3, the symbols DOI1, DOI2, and DOI3 represent the DOI information corresponding to valleys V1, V2, and V3, respectively.

[0045] DOI information can be calculated using Equation 1 above each time scintillation light is generated and there is output from the photodetectors 20A and 20B. By comparing the calculated DOI information with DOI1 to DOI3 (threshold values), the emission position in the Z direction can be determined, that is, the segment in which scintillation light was generated can be identified.

[0046] For example, when the calculated DOI information is less than DOI1, the segment where scintillation light is generated can be identified as Segment (1). Similarly, when DOI1 < the calculated DOI information < DOI2, the segment where scintillation light is generated can be identified as Segment (2). Similarly, when DOI2 < the calculated DOI information < DOI3, the segment where scintillation light is generated can be identified as Segment (3). Similarly, when the calculated DOI information is greater than DOI3, the segment where scintillation light is generated can be identified as Segment (4).

[0047] 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 Figure 5).

[0048] Next, a brief description will be given of a positron emission tomography apparatus 60 (PET (Positron Emission Tomography) apparatus) to which the radiation detector 1 of the present disclosure is applied.

[0049] 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.

[0050] As described above, 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 6 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.

[0051] 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.

[0052] Furthermore, this embodiment has the advantage that calibration in the DOI direction (for determining the gamma-ray interaction position), which was conventionally performed in scintillators that do not form a modified region by laser irradiation, is unnecessary.

[0053] 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 6), and in this way, the generation of scintillation light can be detected in three or more layers.

[0054] 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 7). 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 area of ​​the scintillator blocks can also be reduced. As a result, cost reduction is possible through simplification of scintillator assembly.

[0055] Next, I will explain some variations.

[0056] 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 6 is a perspective view of a modified scintillator 10A. For example, as shown in Figure 6, 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, 11B to each of the first scintillator blocks 11A, 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 of this disclosure.

[0057] Next, we will describe a modified example, scintillator 110.

[0058] Figure 7 is a schematic perspective view of a radiation detector 2 using a modified scintillator 110.

[0059] As shown in Figure 7, the radiation detector 2 includes a scintillator 110 and a photodetection unit 120.

[0060] 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 7). 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 7).

[0061] The material of scintillator 110 is the same as that of scintillator 10, so its explanation is omitted.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Next, the second scintillator block 113 will be described.

[0067] 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.

[0068] 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 7) and the surface of the second scintillator block 113 parallel to the XY plane (lower surfaces in Figure 7) 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.

[0069] 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 7) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 7). 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 7) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 7). 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 7) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 7). 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 7) and the surface of the second scintillator block 113 parallel to the XY plane (lower surface in Figure 7). 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.

[0070] 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.

[0071] Within the scintillator 110 configured as described above, that is, in any of segments (A) to (H), the scintillation light generated propagates to the end faces (lower faces in Figure 7) of the first scintillator blocks 111A, 111B, 111C, and 111D, which are parallel to the XY plane, 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.

[0072] 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.

[0073] First, let's explain how to determine the position in the X and Y directions.

[0074] Figure 8 shows the scintillator 110 as viewed from the direction of arrow AR1 in Figure 7.

[0075] 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.

[0076] 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)").

[0077] Figure 11 is an example of a flood map. In Figure 11, the codes Energy0 to 3 represent the output of the photodetectors 120A to 120D.

[0078] A flood map can be created as follows:

[0079] 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.

[0080]

number

[0081]

number

[0082] Figure 12 is an example flowchart of a method for determining the position in the Z direction.

[0083] 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.

[0084] First, using equations 2-5 above, the emission position in the two-dimensional direction (sum_v xg , sum_h yg Calculate (Step S10).

[0085] 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 threshold values ​​of the flood map (Thx, Thy shown in Figure 13) with the outputs of the photodetectors 120A to 120D. Figure 13 is a diagram showing the frequency distribution (flood map) of gamma-ray events in the two-dimensional direction. In Figure 13, the symbols A1 to A4 each represent regions where gamma-ray events are concentrated (white regions in Figure 13). The threshold values ​​Thx and Thy in Figure 13 may be manually set by visually inspecting the flood map (see, for example, Figure 13), automatically set to an intermediate position between adjacent regions A1 to A4 in the two-dimensional direction, or set by other methods.

[0086] Next, the DOI information is calculated using the following equation 6 (step S12).

[0087]

number

[0088] Figure 9(a) shows the magnitude of the output of the photodetector when scintillation light is generated in segment (C), and Figure 9(b) shows the magnitude of the output of the photodetector when scintillation light is generated in segment (G). Each circle in Figure 9(a) represents the magnitude of the output of photodetectors 120A to 120D when scintillation light is generated in segment (C). Similarly, each circle in Figure 9(b) represents the magnitude of the output of photodetectors 120A to 120D when scintillation light is generated in segment (G). Thus, the ratio of the output of the photodetector 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 DOI information based on photodetector 120C with identification number n=3 is shown in Figure 10, for example. Figure 10 is a histogram summarizing the calculation results of DOI information based on photodetector 120C with identification number n=3. In Figure 10, the vertical axis represents the number of event occurrences, and the horizontal axis represents the DOI information.

[0089] Referring to Figure 10, it can be seen that a valley Va exists between segment (C) and segment (G). In Figure 10, the code DOIa represents the DOI information relative to the photodetector 120C with identification number n=3, which corresponds to the valley Va.

[0090] The DOI information can be calculated using the above Equation 6 each time scintillation light is generated in the segment (C) or segment (G) and outputs are obtained from the light receiving elements 120A to 120D. Then, by comparing the calculated DOI information with the 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.

[0091] For example, when the calculated DOI information < DOIa, the segment where the scintillation light is generated can be identified as the segment (C). Similarly, when DOIa < the calculated DOI information, the segment where the scintillation light is generated can be identified as the segment (G).

[0092] In the same manner as described above, even when scintillation light is generated in the segment (A) or segment (E), the segment (B) or segment (F), or the segment (D) or segment (H), the segment where the scintillation light is generated can be identified.

[0093] Also according to this modified example, the same effects as those of the above-described embodiment can be obtained. 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 there is a one-to-one correspondence between the first scintillator blocks and the light receiving elements, a combination of 3×3, 4×4, 6×12, etc. first scintillator blocks and light receiving elements may be used.

[0094] All the numerical values shown in the above-described embodiment are merely examples, and it goes without saying that appropriate numerical values different from these can be used.

[0095] 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 Symbols

[0096] 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

[0097] (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 array comprising a plurality of first scintillator blocks arranged in parallel to each other in the first layer, A second scintillator block is arranged in the second layer, straddling each of the aforementioned plurality of first scintillator blocks, A reflective member is disposed between the adjacent first scintillator blocks, A first optical discontinuity is provided between each of the plurality of first scintillator blocks and the second scintillator block, A radiation detector comprising a photodetector optically connected to the end face of one of the first scintillator blocks and to the end face of the other first scintillator block.

2. The radiation detector according to claim 1, wherein each of the plurality of first scintillator blocks is partitioned into a plurality of segments by at least one second optical discontinuity.

3. The radiation detector according to claim 1, wherein the plurality of first scintillator blocks are arranged in a matrix in the first layer.

4. The radiation detector according to claim 1, wherein the first optical discontinuity is an optical adhesive layer or an air layer.

5. The radiation detector according to claim 2, wherein the second optical discontinuity is a modified layer, an air layer, or an optical adhesive layer formed by laser irradiation of the first scintillator block.

6. The radiation detector according to claim 1, wherein the photodetection unit includes at least one first photodetector optically connected to the end face of one of the first scintillator blocks, and at least one second photodetector optically connected to the end face of the other first scintillator block.

7. 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 array comprising a plurality of first scintillator blocks arranged in parallel to each other in the first layer, A second scintillator block is arranged in the second layer, straddling each of the aforementioned plurality of first scintillator blocks, A reflective member is disposed between the adjacent first scintillator blocks, A first optical discontinuity is provided between each of the plurality of first scintillator blocks and the second scintillator block, A positron emission tomography apparatus comprising a photodetector optically connected to the end face of one of the first scintillator blocks and to the end face of the other first scintillator block.

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