Radiation detection device and positron emission tomography device

Abstract

The present invention suppresses deterioration of time resolution due to a connection layer connecting a scintillator array and a light receiving element array. A radiation detection device (10) comprises: a scintillator array (11) having a plurality of scintillators (11(i)); a light receiving element array (12) having a plurality of light receiving elements (12(j)) facing the scintillator array, and a translucent connection layer (13) formed on the plurality of light receiving elements and connected to the scintillator array; and a light reflecting member (14) placed in the connection layer along a boundary between the plurality of light receiving elements. The thickness of the light reflecting member is equal to or greater than an interval between the end surfaces of the plurality of scintillator arrays and the light receiving surfaces of the plurality of light receiving elements.

Description

Radiation detection device and positron emission tomography device

[0001] The present invention relates to a radiation detection device and a positron emission tomography device.

[0002] Positron emission tomography (PECT) imaging devices are widely used to generate tomographic images of living organisms by detecting gamma rays emitted from the inside of the organism. In PECT imaging devices, gamma rays are typically detected using a radiation detection device in which detection units, each consisting of a scintillator and a photodetector, are arranged in a matrix.

[0003] To improve the quality of tomographic images, it is important to increase the number of scintillators per unit area to improve the spatial resolution of gamma-ray detection, as well as the temporal resolution. Improving the temporal resolution improves the accuracy of estimating the position of gamma-ray generation on the coincidence line, and ultimately the quality of the tomographic images.

[0004] International Publication No. 2021 / 006061 (WO, A1)

[0005] Generally, a positron emission tomography apparatus is configured by connecting a scintillator array and a photodetector array. That is, a scintillator is optically connected to the light receiving surface of the photodetector (see, for example, Patent Document 1). Generally, the photodetector array has a light-transmitting connection layer (protective layer) to protect the light receiving surface of the photodetector. That is, the scintillator array and the photodetector array are connected by the connection layer.

[0006] As a result of various considerations and experiments, the inventors have found that the time resolution can be reduced due to this connection layer.

[0007] One aspect of the present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a radiation detection device and a positron emission tomography device that suppress the reduction in time resolution caused by the connection layer that connects the scintillator array and the photodetector array.

[0008] a light-receiving element array including a scintillator array having a plurality of scintillators, a plurality of light-receiving elements facing the scintillator array, and a light-transmitting connecting layer formed on the plurality of light-receiving elements and connected to the scintillator array; and a light-reflecting member disposed within the connecting layer along boundaries of the plurality of light-receiving elements, wherein the thickness of the light-reflecting member in a direction perpendicular to a surface of the connecting layer is equal to or greater than the distance between end faces of the plurality of scintillators and light-receiving surfaces of the plurality of light-receiving elements.

[0009] According to one aspect of the present invention, it is possible to provide a radiation detection device and a positron emission tomography device that are designed to suppress a decrease in time resolution caused by a connection layer that connects a scintillator array and a photodetector array.

[0010] FIG. 1 is a perspective view showing an example of the configuration of the radiation detection device according to the first embodiment of the present invention. FIG. 2 is an exploded perspective view showing an example of the configuration of the radiation detection device according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view showing an example of the configuration of the radiation detection device according to the first embodiment of the present invention. FIG. 4 is a flow diagram showing an example of a method for manufacturing the radiation detection device according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view showing a manufactured radiation detection device. FIG. 6 is a schematic view showing an example of the configuration of the radiation detection device according to the first embodiment of the present invention. FIG. 7 is a schematic view showing an example of the configuration of the radiation detection device according to the second embodiment of the present invention. FIG. 8 is a cross-sectional view showing an example of the configuration of the radiation detection device according to the second embodiment of the present invention. FIG. 9 is a perspective view showing an example of a partial configuration of the radiation detection device according to the second embodiment of the present invention. FIG. 10 is a perspective view showing an example of the configuration of a scintillator of the radiation detection device according to the second embodiment of the present invention. FIG. 11 is a perspective view showing another example of the configuration of the scintillator of the radiation detection device according to the second embodiment of the present invention. FIG. 12 is a schematic view showing the configuration of an apparatus for measuring a timing histogram. FIG. 13 is a graph showing a timing histogram in the radiation detection device according to the first embodiment. FIG. 14 is a graph showing a timing histogram in the radiation detection device according to the second embodiment. FIG. 15 is a graph showing a change in time resolution with respect to the thickness of the light reflecting member.

[0011] (Radiation detection apparatus 10 according to first embodiment) The configuration of a radiation detection apparatus 10 according to a first embodiment of the present invention will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a perspective view showing the configuration of the radiation detection apparatus 10 according to the first embodiment of the present invention. Fig. 2 is an exploded perspective view showing the configuration of the radiation detection apparatus 10 according to the first embodiment of the present invention. These figures show xyz coordinates with the vertical direction of the paper as the z direction.

[0012] The radiation detection device 10 is used to detect gamma rays in, for example, a positron emission tomography apparatus. The radiation detection device 10 includes a scintillator array 11, a light receiving element array 12 (having a connection layer 13), and a light reflecting member 14.

[0013] The scintillator array 11 has a plurality of scintillators 11(i) (i is any natural number equal to or greater than 1). Here, a total of 16 scintillators 11(i) are shown, each having a central axis along the z direction and arranged in a matrix in the x and y directions. The scintillators 11(i) are columnar crystals with square bases. The scintillators 11(i) include Ca-doped LYSO (Lutetium Yttrium Orthosilicate), Ce-doped Fast-LGSO (Ce:Lu ｘ Gd （２－ｘ） SiO ５ ), GAGG(Gd3(Ga,Al) ５ O 12 (Ce)), LGSO (Ce:Lu x Gd 2-x SiO5) and LFS (Lutetium Fine Silicate).

[0014] The scintillator array 11 has reflective materials 111 (hereinafter referred to as "inter-scintillator reflective materials") between the plurality of scintillators 11(i) to prevent the mixing of fluorescence between the scintillators 11(i). The inter-scintillator reflective materials 111 have a width W0, which corresponds to the width W of the light reflective member 14 described below.

[0015] The photodetector array 12 faces the scintillator array 11 and has a plurality of photodetectors 12(i). A total of 16 photodetector arrays 12 are shown here, arranged in a matrix in the x and y directions. Each photodetector 12(i) is a plate-shaped element with a square light-receiving surface. Examples of the photodetector 12(i) include MPPC (Multi Pixel photon counter) and PSPMT (Position Sensitive Photo Multiplier Tubes), which are types of SiPM (Silicon Photo Multiplier).

[0016] In this example, one scintillator 11(i) corresponds to one light receiving element 12(i). That is, one scintillator 11(i) faces one light receiving element 12(i) and is connected by a connection layer 13.

[0017] The connection layer 13 is translucent and connects the scintillator array 11 and the light receiving element array 12. That is, the connection layer 13 is formed on the plurality of light receiving elements 12(i) and is connected to the scintillator array 11. Here, the connection layer 13 may be integral, or may be divided into layers for each light receiving element 12(j) that constitutes the light receiving element array 12.

[0018] The multiple scintillators 11(i) are directly connected to the connection layer 13. In other words, no light-transmitting layer such as a light guide is disposed between the multiple scintillators 11(i) and the connection layer 13. The radiation detection device 10 does not have a light guide, and is therefore free from the degradation of time resolution caused by a light guide as in the centroid calculation method described below.

[0019] Some radiation detection devices use a light guide to connect a scintillator and a photodetector, and use centroid calculations to identify the location of the scintillator where gamma rays are incident (hereinafter referred to as the centroid calculation method). Light guides are typically made of transparent acrylic plates several millimeters thick. The light guide spreads the fluorescence from the scintillator and supplies it to multiple photodetectors, thereby reducing the detection error of the photodetectors, even when the scintillator is small relative to the photodetectors. Based on the output ratio of multiple photodetectors, it is possible to accurately detect small scintillators that emit fluorescence. The centroid calculation method allows for light interference between photodetectors due to the light guide, and can detect the location of gamma rays with high spatial resolution by calculating the centroid of the light intensity detected by the photodetectors. However, the centroid calculation method creates optical discontinuities at the light guide connection surface, which induces reflection and absorption at the connection surface, degrading the temporal resolution of the time of gamma ray incidence.

[0020] The connection layer 13 does not function as a light guide for diffusing light to the multiple light receiving elements 12(i). The connection layer 13 is intended to protect the light receiving surfaces of the light receiving elements 12(i), and is not intended to supply light generated by a single gamma ray to the multiple light receiving elements 12(i) as a light guide does. In order to protect the light receiving surfaces of the light receiving elements 12(i), the connection layer 13 is generally made of a more flexible material (e.g., silicone resin) than a light guide. Furthermore, the connection layer 13 is thinner than a light guide (thickness: several mm or more). For example, the thickness of the connection layer 13 is thinner than 0.5 mm (e.g., approximately 0.1 to 0.2 mm).

[0021] The connection layer 13 can be integrally configured as the entire radiation detection device 10. Alternatively, the connection layer 13 may be divided for each light receiving element 12(i). In this case, the connection layer 13 is divided into a plurality of regions corresponding to the light receiving elements 12(i).

[0022] The light reflecting member 14 is disposed within the connection layer 13 along the boundaries of the plurality of light receiving elements 12(i). The light reflecting member 14 has a lattice shape that follows the boundaries (square in this case) of the plurality of light receiving elements 12(i), and is disposed within the connection layer 13. The light reflecting member 14 is generally not disposed on the light receiving surface (sensible region: square shape) of the light receiving element 12(i), but is disposed on the insensitive region (lattice shape). The light reflecting member 14 may have an outer periphery 141 that follows the outer periphery of the light receiving element array 12.

[0023] The thickness D of light reflecting member 14, i.e., the thickness D in the direction perpendicular to the surface of connecting layer 13 (z-axis direction), is equal to or greater than the distance T between the end faces of the plurality of scintillators 11(i) and the light receiving surfaces of the plurality of light receiving elements 12(i). The width W of light reflecting member 14 is preferably equal to or less than the width W0 of inter-scintillator reflecting material 111. This is to allow light from scintillators 11(i) to reach light receiving elements 12(i) without being obstructed by light reflecting member 14.

[0024] Here, the light receiving element array 12 has grooves G at the boundaries between the multiple light receiving elements 12(i), and the light reflecting members 14 are inserted into the grooves G. Here, the grooves G are formed in the integral connection layer 13 of the entire radiation detection device 10. On the other hand, if the connection layer 13 is divided into regions for each light receiving element 12(i), the spaces (gaps) between the connection layer 13 in each region function as the grooves G, making it unnecessary to form grooves G in the connection layer 13.

[0025] The light reflecting member 14 may be formed of a solid such as a reflective film (for example, a film of a resin material containing a metal oxide), or may be made of powder. ４ The light reflecting member 14 can be formed by filling the powder of the above-mentioned material.

[0026] 3 is a cross-sectional view showing an example of the configuration of the radiation detection device according to the first embodiment of the present invention, which shows a state in which a gamma ray is incident on position P of scintillator 11(2) among scintillators 11(1) to 11(3) and light is generated.

[0027] Fluorescence is generated at position P. Fluorescence L1 travels through the connection layer 13 toward the scintillator 11(1), and fluorescence L2 travels through the connection layer 13 toward the scintillator 11(3). In this respect, the connection layer 13 functions, albeit to a small extent, as a light guide. If the light reflecting member 14 were not present, these fluorescence beams L1 and L2 would not be incident on the light receiving surface (sensitive region) of the light receiving element 12(2), but would tend to be incident on the insensitive region between the light receiving elements 12(i). The light receiving element array 12 has insensitive regions between the light receiving elements 12(i) that are, for example, about 10 to 20 percent of the sensitive region (light receiving surface), and fluorescence that enters the insensitive region would not be detected.

[0028] However, in this embodiment, the fluorescence L1 and L2 are reflected by the light reflecting member 14 disposed at the boundary between the light receiving elements 12(i) and are incident on the light receiving surface of the light receiving element 12(2). As a result, the proportion of the fluorescence generated in the scintillator 11(2) that is incident on the light receiving element 12(2) (light collection efficiency) can be improved. This contributes to improving the time resolution of the fluorescence, as will be shown in the examples described later.

[0029] Fig. 4 is a flow chart showing an example of a method for manufacturing the radiation detection device 10 according to the first embodiment of the present invention, and Fig. 5 is a cross-sectional view showing the radiation detection device 10 to be manufactured.

[0030] (1) Preparation of Light-Receiving Element Array 12 (Step S11, FIG. 5(a)) The light-receiving element array 12 is prepared. The light-receiving element array 12 has a connection layer 13 formed on the light-receiving elements 12(i). The connection layer 13 may be formed so as to be separated for each light-receiving element 12(i), but in this example, the connection layer 13 is formed to integrally cover the entire upper surface of the light-receiving element array 12.

[0031] (2) Formation of Grooves G (Step S12, FIG. 5(b)) A lattice-shaped groove G is formed in the connection layer 13 along the boundaries of the light-receiving elements 12(i). If the connection layer 13 is formed so as to be divided into sections for each light-receiving element 12(i), this step is unnecessary because the gaps between the divided connection layer 13 function as the grooves G.

[0032] (3) Formation of Light Reflecting Member 14 in Groove G (Step S13, FIG. 5C) The light reflecting member 14 is formed in the groove G. For example, the light reflecting member 14 can be formed by filling the groove G with a light reflecting material having light reflectivity. As this light reflecting material, for example, powder, for example, barium sulfate (BaSO ４ ) powder can be used.

[0033] (4) Connecting the light-receiving element array 12 and the scintillator array 11 (step S14) For example, the scintillator array 11 is connected and fixed to the light-receiving element array 12 by an optical adhesive. At this time, the connection layer 13 is interposed between the light-receiving element array 12 and the scintillator array 11, so that the scintillator 11(i) prevents damage to the light-receiving surfaces of the light-receiving elements 12(i).

[0034] (Configuration and Operation of Positron Emission Tomography Apparatus) The configuration and operation of a positron emission tomography apparatus 50 including the radiation detection device 10 described above will be described with reference to FIG.

[0035] 6 is a block diagram of a positron emission tomography apparatus 50. The positron emission tomography apparatus 50 includes the radiation detection apparatus 10 described above and a signal processing apparatus 20 that processes output signals from the radiation detection apparatus 10. When a gamma ray is incident on any of the scintillators 11(i) that make up the scintillator array 11, the radiation detection apparatus 10 outputs a detection signal. The signal processing apparatus 20 processes the detection signal to generate a cross-sectional image of the location where the gamma ray is emitted.

[0036] As described above, in the first embodiment, by arranging the light reflecting member 14 at the boundary of the light receiving element 12(i), the proportion (light collection rate) of the fluorescence generated in the scintillator 11(i) that is incident on the light receiving element 12(i) that is directly optically connected to the scintillator 11(i) can be improved, thereby improving the time resolution of the fluorescence.

[0037] (Radiation detection apparatus 10 according to second embodiment) The configuration of a radiation detection apparatus 10 according to a second embodiment of the present invention will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing an example of the configuration of the radiation detection apparatus 10 according to the second embodiment of the present invention. Fig. 7(a) shows the radiation detection apparatus 10 according to the second embodiment as viewed from the negative direction of the Y axis. Fig. 7(b) shows the radiation detection apparatus 10 according to the second embodiment as viewed from the positive direction of the Z axis.

[0038] Similar to the radiation detection device 10 according to the first embodiment, the radiation detection device 10 according to the second embodiment includes a scintillator array 11, a light receiving element array 12, a connection layer 13, and a light reflecting member 14. However, whereas in the first embodiment, one scintillator 11(i) corresponds to one light receiving element 12(i), in the second embodiment, multiple scintillators 11(i) correspond to one light receiving element 12(i) among the multiple light receiving elements 12(i). In other words, multiple (four in this case) scintillators 11(i) face one light receiving element 12(i) and are connected by the connection layer 13. However, on the outer periphery of the light receiving element array 12, one scintillator 11(i) faces and is connected to one light receiving element 12(i).

[0039] Fig. 8 is a cross-sectional view showing an example of the configuration of a radiation detection device 10 according to a second embodiment of the present invention. (a), (b), and (c) of Fig. 8 respectively show the radiation detection device 10 cut along planes Sa, Sb, and Sc parallel to the xy plane shown in Fig. 7. Fig. 7 shows parts of the scintillator array 11 and the photodetector array 12 as a basic scintillator array 11p and a basic photodetector array 12p.

[0040] The basic scintillator array 11p includes multiple scintillators 11(1-1) to 11(4-2). Scintillators 11(i-1) and 11(i-2) form pairs to form scintillator units 11U(i) (i = 1 to 4). The shapes and configurations of the scintillators 11(i-1) and 11(i-2) are similar to those of the scintillators (i) according to the first embodiment, and therefore detailed descriptions thereof will be omitted.

[0041] The basic light receiving element array 12p includes a plurality of light receiving elements 12(1) to 12(9) arranged in a matrix. The area of ​​the bottom surface of the light receiving element 12(j) is four times the area of ​​the bottom surfaces of the scintillators 11(i-1) and 11(i-2). The shape and configuration of the light receiving element 12(j) are similar to those of the light receiving element 12(j) according to the first embodiment, and therefore detailed description thereof will be omitted.

[0042] The bottom surfaces of the scintillators 11(1-1), 11(2-1), 11(3-1), and 11(4-1) are optically connected to the light-receiving surface of the light-receiving element 12(1) located at the center of the basic light-receiving element array 12p. The bottom surfaces of the scintillators 11(1-2), 11(2-2), 11(3-2), and 11(4-2) are optically connected to the light-receiving surfaces of the light-receiving elements 12(2), 12(3), 12(4), and 12(5) adjacent to the light-receiving element 12(1).

[0043] The configuration of the scintillator unit 11U(i), i.e., the scintillators 11(i-1) and 11(i-2), will be described with reference to Figures 10 and 11. Figures 10 and 11 are perspective views showing an example of the configuration of the scintillators of the radiation detection device 10 according to the second embodiment of the present invention.

[0044] The scintillators 11(i-1) and 11(i-2) have one or two roughened sides.

[0045] In Figure 10, one side surface of each of scintillators 11(i-1) and 11(i-2) is roughened. The side surface F1(i-1) of scintillator 11(i-1) is roughened and is optically connected to scintillator 11(i-2). The area of ​​the side surface F1(i-1) below the z-axis is covered with a reflective material. In addition, the side surfaces F2(i-1) to F4(i-1) and the bottom surface F6(i-1) of scintillator 11(i-1) are entirely covered with a reflective material.

[0046] Of the side surfaces F1(i-1) and F1(i-2), the areas above the z axis that are not covered with the reflective material are bonded with an optical adhesive. That is, the upper z axis sides of the scintillators 11(i-1) and 11(i-2) are optically connected.

[0047] In FIG. 11, two side surfaces of each of scintillators 11(i-1) and 11(i-2) are roughened. Side surfaces F1(i-1) and F4(i-1) of scintillator 11(i-1) are roughened. Side surface F1(i-1) is optically connected to scintillator 11(i-2). The area of ​​side surface F1(i-1) below the z-axis is covered with a reflective material. In addition, side surfaces F2(i-1) to F4(i-1) and the bottom surface F6(i-1) of scintillator 11(i-1) are entirely covered with a reflective material.

[0048] Of the side surfaces F1(i-1) and F1(i-2), the areas above the z axis that are not covered with the reflective material are bonded with an optical adhesive. That is, the upper z axis sides of the scintillators 11(i-1) and 11(i-2) are optically connected.

[0049] 10 and 11, the plurality of light receiving elements 12(j) includes a first light receiving element 12(j) and a second light receiving element 12(k) adjacent to the first light receiving element. The plurality of scintillators 11(i) includes a first scintillator 11(i-1) including a first bottom surface F5(i-1) and a first side surface F1(i-1) connected to the light receiving surface of the first light receiving element 12(j) by the connection layer 13, and a second scintillator 11(i-2) having a second bottom surface F5(i-2) connected to the light receiving surface of the second light receiving element 12(k) by the connection layer 13 and a second side surface F2(i-2) optically connected to a portion of the first side surface F1(i-1).

[0050] In this way, the upper z-axis sides of the scintillators 11(i-1) and 11(i-2) are optically connected. This allows the fluorescence generated in one of the scintillators 11(i-1) and 11(i-2) to enter the other. As a result, the multiple light-receiving elements 12(j) detect the fluorescence.

[0051] For example, fluorescence generated in one of scintillators 11(1-1) and 11(1-2) enters the other and is detected by both light-receiving elements 12(1) and 12(2). When fluorescence is generated in scintillator 11(1-1), light-receiving elements 12(1) and 12(2) detect relatively strong and weak fluorescence, respectively. On the other hand, when fluorescence is generated in scintillator 11(1-2), light-receiving elements 12(1) and 12(2) detect relatively weak and strong fluorescence, respectively.

[0052] That is, in the radiation detection device 10 according to the second embodiment, a pair of adjacent light receiving elements 12(j) and 12(k) receive fluorescence upon incidence of a single radiation. At this time, it is considered that the radiation is incident on a pair of scintillators 11(i-1) and 12(i-2) corresponding to the light receiving elements 12(j) and 12(k), respectively. By comparing the detection intensities of the light receiving elements 12(j) and 12(k), it is possible to determine that the radiation is incident on the scintillator 11(i-1) or 12(i-2) corresponding to the stronger detection intensity. As a result, it is possible to improve the resolution of radiation detection rather than the size of the light receiving element 12(i) itself. In the second embodiment, the signal processing device 20 executes a first identification process and a second identification process, which will be described later, to identify the scintillator on which the radiation is incident and the position of incidence of the radiation on that scintillator.

[0053] In this way, in the radiation detection device 10 according to the second embodiment, by associating a plurality of scintillators with one light receiving element 12(i), it is possible to improve the detection resolution. Furthermore, as in the first embodiment, by arranging light reflecting members 14 at the boundaries of the light receiving elements 12(i), it is possible to improve the proportion (light collection efficiency) of the fluorescence generated in the scintillator 11(i) that is incident on the light receiving element 12(i), and thereby improve the time resolution of the fluorescence.

[0054] (Configuration and Operation of Positron Emission Tomography Apparatus) As in the first embodiment, a positron emission tomography apparatus 50 can be configured that includes the radiation detection apparatus 10 according to the second embodiment, as shown in FIG. 6 . In this case, the signal processing device 20 executes the following first identification process and second identification process. In the first identification process, the pair of scintillators 11(i-1) and 11(i-2) onto which radiation is incident is identified based on the combination of two light receiving elements 12(j) and 11(k) that detect fluorescence in the light receiving element array 12. In the second identification process, the scintillators (i-1) and 11(i-2) onto which radiation is incident and the position of incidence of the radiation on these scintillators are identified based on the ratio (magnitude relationship) of the fluorescence intensities detected by the two light receiving elements 12(i-1) and 11(i-2).

[0055] (Example of Radiation Detector 10) An example of the radiation detector 10 according to the first and second embodiments will be described with reference to Fig. 6 and Fig. 7. The radiation detector 10 according to the first and second embodiments was created and timing histograms were measured as follows.

[0056] A Fast LGSO was used as the scintillator array 11, and an MPPC was used as the light-receiving element array 12. A 75 μm-thick lumirror was used as the inter-scintillator reflector 111. The MPPC had a connection layer 13 made of a 15 μm-thick silicone resin film. A lattice-shaped groove G (slit) was formed in the light-receiving element array 12, and a barium sulfate powder was filled in the groove G to form a light-reflecting member 14. The groove G was formed along the boundary (insensitive region) between the light-receiving elements 12(i) of the light-receiving element array 12. The groove G had a width W of 80 μm, and a thickness D of 50 μm, 100 μm, 150 μm, and 350 μm. A radiation detection device 10 without a light-reflecting member 14 was used as a comparative example. The thickness D of the light-reflecting member 14 of this comparative example can be treated as zero.

[0057] FIG. 12 is a schematic diagram showing the configuration of an apparatus for measuring a timing histogram. A pair of radiation detection devices 10a and 10b, created under the same conditions, are arranged facing each other, with a gamma-ray source SP located midway between them. A pair of gamma rays is emitted from the source SP in opposite directions. Therefore, the radiation detection devices 10a and 10b essentially detect the pair of gamma rays simultaneously. For this reason, a histogram was created based on the difference in detection time between the radiation detection devices 10a and 10b. The half-width of this histogram represents the time resolution of the radiation detection devices 10a and 10b.

[0058] 13 and 14 are graphs showing timing histograms for the radiation detection apparatuses according to the first and second embodiments, respectively. (a), (b), (c), (d), and (e) in Fig. 13 and Fig. 14 correspond to thicknesses D of the light reflecting member 14 of 0, 50, 100, 150, and 350 μm, respectively. The width (half-width) of the timing histogram varies from 235.5 to 211.0 ps in Fig. 13 and from 207.8 to 198.0 ps in Fig. 14 in response to the thickness D.

[0059] FIG. 15 is a graph showing the change in temporal resolution (half-width) versus the thickness D of the light-reflecting member 14. (a) and (b) of FIG. 15 correspond to FIGS. 13 and 14, respectively. In both the first and second embodiments, the temporal resolution is improved by providing the light-reflecting member 14. The temporal resolution improves as the thickness D of the light-reflecting member 14 increases. The temporal resolution is particularly improved when the thickness D of the light-reflecting member 14 reaches the distance T between the end face of the scintillator 11(i) and the light-receiving surface of the light-receiving element 12(i) (here, D = T = 150 μm). In this case, in the first embodiment, the temporal resolution improves by 13 ps, from 235.5 ps to 212.5 ps, and in the second embodiment, the temporal resolution improves by 8.9 ps, from 207.8 ps to 198.9 ps.

[0060] (Summary) A radiation detection device according to a first aspect of this embodiment includes a light-receiving element array including a scintillator array having a plurality of scintillators, a plurality of light-receiving elements facing the scintillator array, and a light-transmitting connection layer formed on the plurality of light-receiving elements and connected to the scintillator array, and a light-reflecting member disposed within the connection layer along the boundaries of the plurality of light-receiving elements, wherein the thickness of the light-reflecting member in a direction perpendicular to a surface of the connection layer is equal to or greater than the distance between end faces of the plurality of scintillators and the light-receiving surfaces of the plurality of light-receiving elements, thereby enabling improvement of time resolution.

[0061] A radiation detection device according to Aspect 2 of this embodiment is the same as Aspect 1, except that the photodetector array has grooves at boundaries between the plurality of photodetectors, and the light reflecting member is inserted into the grooves, thereby enabling further improvement in time resolution.

[0062] A radiation detection device according to Aspect 3 of the present embodiment is the same as Aspect 1 or 2, in that the plurality of scintillators are directly connected to the connection layer, thereby eliminating the need for a light guide or the like between the scintillators and the connection layer, thereby enabling further improvement in time resolution.

[0063] A radiation detection device according to Aspect 4 of this embodiment is any one of Aspects 1 to 3, wherein the thickness of the connection layer is less than 0.5 mm. A thin light-reflecting member can reduce light leakage between adjacent light-receiving elements. This prevents the connection layer from performing the function of diffusing light between light-receiving elements, as a light guide would, thereby improving the time resolution.

[0064] A radiation detection device according to Aspect 5 of the present embodiment is the radiation detection device of any one of Aspects 1 to 4, wherein the light reflecting member is made of powder. The light reflecting member can be easily formed using a powder reflective material.

[0065] A radiation detection device according to Aspect 6 of the present embodiment is the radiation detection device of any one of Aspects 1 to 5, wherein one scintillator among the plurality of scintillators corresponds to one light receiving element among the plurality of light receiving elements. The light receiving elements and scintillators are in one-to-one correspondence, making it possible to clarify the correspondence relationship.

[0066] A radiation detection device according to Aspect 7 of the present embodiment is the radiation detection device of any one of Aspects 1 to 5, wherein a plurality of scintillators among the plurality of scintillators correspond to one light receiving element among the plurality of light receiving elements. By associating a plurality of scintillators with one light receiving element, spatial resolution can be improved.

[0067] A radiation detection device according to Aspect 8 of the present embodiment is the radiation detection device of any of Aspects 1 to 7 above, wherein the plurality of light receiving elements include a first light receiving element and a second light receiving element adjacent to the first light receiving element, and the plurality of scintillators include a first scintillator including a first bottom surface and a first side surface connected to a light receiving surface of the first light receiving element by the connection layer, and a second scintillator having a second bottom surface connected to a light receiving surface of the second light receiving element by the connection layer and a second side surface optically connected to a portion of the first side surface. By connecting the first and second scintillators, portions of which are optically connected, to the first and second light receiving elements, respectively, it is possible to determine which of the first and second scintillators has been incident on, with the plurality of scintillators corresponding to one light receiving element.

[0068] A positron emission tomography apparatus according to Aspect 9 of this embodiment includes the radiation detection apparatus according to any one of Aspects 1 to 8. This makes it possible to improve the time resolution of the positron emission tomography apparatus.

[0069] (Additional Notes) The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0070] REFERENCE SIGNS LIST 10 Radiation detection device 11 Scintillator array 11(i) Scintillator 12 Light receiving element array 12(j) Light receiving element 13 Connection layer 14 Light reflecting member 20 Signal processing device 50 Positron emission tomography device

Claims

1. A radiation detection device comprising: a scintillator array having a plurality of scintillators; a plurality of light receiving elements facing the scintillator array; and a light receiving element array having a translucent connecting layer formed on the plurality of light receiving elements and connected to the scintillator array; and a light reflecting member disposed within the connecting layer along the boundaries of the plurality of light receiving elements, wherein the thickness of the light reflecting member in a direction perpendicular to the surface of the connecting layer is equal to or greater than the distance between the end faces of the plurality of scintillators and the light receiving surfaces of the plurality of light receiving elements.

2. The radiation detection device according to claim 1, wherein the light receiving element array has grooves at boundaries between the plurality of light receiving elements, and the light reflecting member is inserted into the grooves.

3. The radiation detection device according to claim 1 or 2, wherein the plurality of scintillators are directly connected to the connection layer.

4. A radiation detection device according to any one of claims 1 to 3, wherein the thickness of the connection layer is less than 0.5 mm.

5. A radiation detection device according to any one of claims 1 to 4, wherein the light reflecting member is made of powder.

6. A radiation detection device according to any one of claims 1 to 5, wherein one of said plurality of scintillators corresponds to one of said plurality of light receiving elements.

7. A radiation detection device according to any one of claims 1 to 5, wherein a plurality of scintillators among said plurality of scintillators correspond to one light receiving element among said plurality of light receiving elements.

8. A radiation detection device as claimed in any one of claims 1 to 7, wherein the plurality of light receiving elements include a first light receiving element and a second light receiving element adjacent to the first light receiving element, and the plurality of scintillators include a first scintillator including a first bottom surface and a first side surface connected to the light receiving surface of the first light receiving element by the connection layer, and a second scintillator having a second bottom surface connected to the light receiving surface of the second light receiving element by the connection layer, and a second side surface optically connected to a portion of the first side surface.

9. A positron emission tomography apparatus comprising a radiation detection device according to any one of claims 1 to 8.

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