Measurement device and measurement method

Abstract

A measurement device (10) is provided with an attenuator (120), a scatterer (140), and an absorber (160). The attenuator (120) transmits incident gamma rays (20) with a probability corresponding to an incident angle. The scatterer (140) scatters at least part of the gamma rays (20) transmitted through the attenuator (120). The absorber (160) absorbs at least part of the gamma rays (20) scattered by the scatterer (140). In one example, a first generation unit uses the scattering position information, absorption position information, first emission energy value, and second emission energy value of the gamma rays (20) to generate first distribution information relating to the direction of incidence of the gamma rays (20) on the attenuator (120).

Description

Measuring device and measuring method

[0001] The present invention relates to a measurement device and a measurement method.

[0002] A Compton camera is a device that detects the direction from which gamma rays arrive. Compton cameras are used in the fields of physics, astronomy, medicine, and the environment, for example.

[0003] Non-Patent Document 1 describes a technique for simultaneously imaging the distribution of two types of radiopharmaceuticals (SPECT agent and PET agent) in the human body using one Compton camera.

[0004] Non-Patent Document 2 describes a technique for simultaneously performing PET imaging and Compton imaging.

[0005] Takashi Nakano and 14 others, "Imaging of 99mTc-DMSA and 18F-FDG in humans using a Si / CdTe Compton camera," Physics in Medicine & Biology, IOP Publishing, February 28, 2020, 65 (2020) 05LT01 Mizuki Uenomachi and 7 others, "Simultaneous in vivo imaging with PET and SPECT tracers using a Compton-PET hybrid camera," Scientific Reports, Nature Research, September 9, 2021, (2021) 11:17933

[0006] However, in the technology of Non-Patent Document 1, the distribution of two drugs was imaged using only a Compton camera. As a result, the resolution of both drugs was poor compared to that of a normal SPECT device and a PET device, and there was a problem that it was not suitable for practical use. In addition, in the technology of Non-Patent Document 2, a general-purpose SPECT drug was used. ９９ｍ Tc is difficult to image, emits multiple photons, and ９９ｍ A special agent that emits gamma rays with higher energy than Tc １１１ In was used.

[0007] The present invention provides a radiation measurement device that is highly versatile and accurate.

[0008] According to one aspect of the present invention, the following measurement device and measurement method are provided.

[0009] 1. A measuring device comprising: an attenuator that transmits incident gamma rays with a probability according to the angle of incidence; a scatterer that scatters at least a portion of the gamma rays that have transmitted through the attenuator; and an absorber that absorbs at least a portion of the gamma rays scattered by the scatterer. 2. The measuring device described in 1., further comprising a first generation unit that generates first distribution information regarding the incident direction of the gamma rays on the attenuator using scattering position information of the gamma rays in the scatterer, absorption position information of the gamma rays in the absorber, a first emission energy value from the gamma rays to the scatterer, and a second emission energy value from the gamma rays to the absorber. 3. The measuring device described in 2., wherein the attenuator has an attenuation unit that attenuates the number of gamma rays, and the first generation unit generates the first distribution information further using a passage length assumed to be taken by the gamma rays through the attenuation unit. 4.3. 5. The measuring device described in any one of 1. to 4., wherein the attenuator is a parallel collimator. 6. The measuring device described in 5., further comprising a second generator configured to generate arrival information regarding the origin of a gamma ray by using absorption position information in the scatterer of gamma rays absorbed in the scatterer. 7. The measuring device described in any one of 1. to 4., wherein the attenuator is a parallel collimator. 6. The measuring device described in 5., further comprising a second generator configured to generate arrival information regarding the origin of a gamma ray by using absorption position information in the scatterer of gamma rays absorbed in the scatterer. 7. The measuring device described in 1. to 6., wherein the first generator specifies a distribution of candidate positions through which a gamma ray may have passed within the object plane, using the scattering position information, the absorption position information, the first emission energy value, and the second emission energy value of the gamma ray, 2. The measuring device according to claim 1, wherein the distance between the attenuating body and the scattering body is 5 mm or less.8. A measurement method comprising: making gamma rays incident on an attenuator that transmits the incident gamma rays with a probability according to the angle of incidence; scattering at least a portion of the gamma rays that have transmitted through the attenuator by a scatterer; and absorbing at least a portion of the gamma rays scattered by the scatterer by an absorber.

[0010] According to the present invention, it is possible to provide a radiation measuring device that is highly versatile and accurate.

[0011] FIG. 1 is a diagram illustrating a configuration of a measurement device according to a first embodiment; FIG. 2 is a diagram illustrating an example of an attenuator according to the first embodiment; FIG. 3 is a diagram illustrating a configuration of a detector for realizing a scatterer and an absorber; FIG. 4 is a diagram illustrating a configuration of a measurement device according to a first embodiment; FIG. 5 is a diagram illustrating a computer for realizing a first generation unit; and FIG. 6 is a diagram illustrating a relationship between an attenuator, a scatterer, and an absorber and gamma rays incident thereon. １ 1 is a diagram illustrating an example of the positional relationship between a point P and an ellipse. １ and point P Ｃ FIG. 1 is a diagram illustrating a positional relationship between the attenuation unit and the scattering position (point P １ ), and the candidate position (point P Ｃ 22 and 23. FIG. 23 is a diagram showing a relationship between the cumulative distribution information of the first embodiment and the cumulative distribution information of the first comparative example. FIG. 24 is a diagram showing a measurement configuration according to the first embodiment. FIG. 25 is a diagram showing cumulative distribution information according to the first comparative example. FIG. 26 is a diagram showing a line profile of the cumulative distribution information shown in each of FIGS. 18 and 19. FIG. 27 is a diagram showing a measurement configuration according to the second embodiment. FIG. 28 is a diagram showing cumulative distribution information according to the second comparative example. FIG. 29 is a diagram showing a line profile of the cumulative distribution information shown in each of FIGS. 22 and 23.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, like components are designated by like reference numerals, and the description thereof will be omitted as appropriate.

[0013] First Embodiment FIG. 1 is a diagram illustrating the configuration of a measurement device 10 according to a first embodiment. In FIG. 1, a gamma ray source is indicated by a black circle. The measurement device 10 according to this embodiment includes an attenuator 120, a scatterer 140, and an absorber 160. The attenuator 120 transmits incident gamma rays 20 with a probability according to the angle of incidence. The scatterer 140 scatters at least a portion of the gamma rays 20 that have transmitted through the attenuator 120. The absorber 160 absorbs at least a portion of the gamma rays 20 scattered by the scatterer 140.

[0014] The measurement method according to this embodiment includes making gamma rays incident on the attenuator 120, scattering at least a portion of the gamma rays 20 that have passed through the attenuator 120 by the scatterer 140, and absorbing at least a portion of the gamma rays 20 scattered by the scatterer 140 by the absorber 160. Here, the attenuator 120 transmits the incident gamma rays 20 with a probability that depends on the angle of incidence.

[0015] The measurement method according to this embodiment is realized, for example, by the measurement device 10 according to this embodiment.

[0016] According to the measurement device 10 and measurement method of this embodiment, it is possible to measure with high accuracy the direction from which the gamma rays 20 have arrived by using the attenuator 120. The measurement device 10 and measurement method of this embodiment will be described in detail below.

[0017] 2 is a diagram showing an example of the attenuator 120 according to this embodiment. As described above, the attenuator 120 transmits incident gamma rays 20 with a probability that depends on the angle of incidence. Note that the attenuator 120 does not need to transmit gamma rays 20 of all energy bands with a probability that depends on the angle of incidence. The attenuator 120 only needs to transmit gamma rays 20 of at least one energy band (for example, gamma rays 20 of a high-energy band described below) with a probability that depends on the angle of incidence. For example, the attenuator 120 may be one that blocks gamma rays 20 of other energy bands regardless of the angle of incidence.

[0018] The attenuator 120 has an attenuation section 122 that attenuates the number of gamma rays 20. That is, when multiple gamma rays 20 enter the attenuation section 122, only a portion of the multiple gamma rays 20 pass through the attenuation section 122. The probability that the gamma rays 20 will pass through the attenuation section 122 depends on the energy of the gamma rays 20, etc. The attenuation section 122 is made of, for example, a metal that attenuates the number of gamma rays 20. The attenuation section 122 contains, for example, at least one of tungsten, lead, tin, and copper. Alternatively, the attenuation section 122 may contain an alloy containing at least one of tungsten, lead, tin, and copper. In the example of FIG. 2 , the attenuation section 122 is a flat metal plate. Furthermore, the entire attenuation body 120 is the attenuation section 122. The thickness of the attenuation body 120 according to this embodiment is, for example, 3 mm or more and 15 mm or less.

[0019] The probability that the gamma rays 20 will pass through the attenuation section 122 decreases as the length L of the gamma rays 20 passing through the attenuation section 122 increases. In other words, the larger the angle of incidence of the gamma rays 20 with respect to the incident surface 120a of the attenuation body 120, the lower the possibility that the gamma rays 20 will pass through the attenuation body 120 without being absorbed by the attenuation section 122.

[0020] 2 , the attenuator 120 is generally flat. An incident surface 120a of the attenuator 120 is one of the main surfaces of the attenuator 120. An exit surface 120b of the attenuator 120 is the other of the main surfaces of the attenuator 120, and is the surface opposite to the incident surface 120a of the attenuator 120. The exit angle of the gamma rays 20 from the attenuator 120 is the same as the incident angle of the gamma rays 20 into the attenuator 120.

[0021] The incident angle of the gamma rays 20 with respect to the incident surface is the angle between the normal to the incident surface and the incident direction of the gamma rays 20. The exit angle of the gamma rays 20 with respect to the exit surface is the angle between the normal to the exit surface and the exit direction of the gamma rays 20. Hereinafter, the same applies to the incident angle and exit angle with respect to each member.

[0022] The scatterer 140 scatters the gamma rays 20 that are incident on the scatterer 140. That is, the angle at which the gamma rays 20 are emitted from the scatterer 140 may differ from the angle at which the gamma rays 20 are incident on the scatterer 140. For example, the scatterer 140 is generally flat. The incident surface 140a of the scatterer 140 is one of the main surfaces of the scatterer 140. The exit surface 140b of the scatterer 140 is the other of the main surfaces of the scatterer 140, and is the surface opposite the incident surface 140a of the scatterer 140.

[0023] The exit surface 120b of the attenuator 120 faces the incident surface 140a of the scatterer 140. The exit surface 120b of the attenuator 120 is parallel to the incident surface 140a of the scatterer 140. The distance between the attenuator 120 and the scatterer 140 is preferably 5 mm or less, and more preferably 1 mm or less. The narrower the distance between the attenuator 120 and the scatterer 140, the less susceptible to external influences, improving the measurement accuracy of the measurement device 10. It is more preferable that the attenuator 120 and the scatterer 140 are in contact with each other. In other words, it is preferable that the exit surface 120b of the attenuator 120 is in contact with the incident surface 140a of the scatterer 140. However, another member that does not affect the gamma rays 20 may be interposed between the attenuator 120 and the scatterer 140.

[0024] The scatterer 140 receives energy from the gamma rays 20 scattered within the scatterer 140. That is, the energy of the gamma rays 20 attenuates within the scatterer 140. The scatterer 140 has a function of detecting the magnitude of energy emitted from the gamma rays 20 to the scatterer 140 (referred to as the "first emitted energy value"). The scatterer 140 also has a function of detecting the position at which the gamma rays 20 are scattered within the scatterer 140 (referred to as the "scattering position"). The scatterer 140 may have a function of detecting the scattering position in two dimensions or in three dimensions. The scatterer 140 is realized, for example, by a detector 30, which will be described in detail later using FIG. 3.

[0025] The absorber 160 absorbs the gamma rays 20 that are incident on the absorber 160. That is, the gamma rays 20 that are incident on the absorber 160 lose energy within the absorber 160 and are not emitted from the absorber 160. For example, the absorber 160 has a flat plate shape as a whole. The incident surface 160a of the absorber 160 is one of the main surfaces of the absorber 160.

[0026] The exit surface 140b of the scatterer 140 faces the incident surface 160a of the absorber 160. The exit surface 140b of the scatterer 140 is parallel to the incident surface 160a of the absorber 160. The distance between the scatterer 140 and the absorber 160 can be set according to the target resolution and sensitivity. The scatterer 140 and the absorber 160 may be in contact with each other or may be spaced apart. When the scatterer 140 and the absorber 160 are in contact with each other, high sensitivity is obtained but resolution decreases. Conversely, widening the distance between the scatterer 140 and the absorber 160 can increase resolution but decrease sensitivity and narrow the field of view. The distance between the scatterer 140 and the absorber 160 is preferably 30 mm or more and 50 mm or less. The distance between the scatterer 140 and the absorber 160 may be 50 mm or more.

[0027] The absorber 160 receives energy from the gamma rays 20 absorbed within the absorber 160. That is, the energy of the gamma rays 20 attenuates within the absorber 160. The absorber 160 has a function of detecting the magnitude of energy emitted from the gamma rays 20 to the absorber 160 (referred to as the "second emitted energy value"). The absorber 160 also has a function of detecting the position at which the gamma rays 20 are absorbed within the absorber 160 (referred to as the "absorption position"). The absorber 160 may have a function of detecting the absorption position in two dimensions or in three dimensions. The absorber 160 is realized, for example, by the detector 30, which will be described in detail later using FIG. 3.

[0028] The attenuating body 120, the scattering body 140, and the absorber 160 are arranged in this order in the measuring device 10. The relative positions of the attenuating body 120, the scattering body 140, and the absorber 160 are fixed relative to one another.

[0029] FIG. 3 is a diagram illustrating a configuration of a detector 30 for realizing the scatterer 140 and the absorber 160. The detector 30 includes an array of scintillators 31 and an array of photoelectric conversion elements 32. The scintillator 31 converts the energy emitted by the gamma rays 20 into light and outputs the light. The photoelectric conversion elements 32 convert the light output from the scintillator 31 into an electrical signal. The photoelectric conversion elements 32 are, for example, photomultiplier tubes (PMTs), photodiodes, or optical elements with internal amplification functions (avalanche photodiodes or silicon photomultipliers). The array of photoelectric conversion elements 32 is, for example, an array of PMTs, an array of photodiodes, an array of avalanche photodiodes, or an array of silicon photomultipliers. An example of a silicon photomultiplier that can be arrayed is a multi-pixel photon counter (MPPC).

[0030] In the example of Fig. 3, the detector 30 detects the position at which the gamma ray 20 emits energy in two dimensions. That is, the plurality of scintillators 31 are arrayed two-dimensionally. Furthermore, the plurality of photoelectric conversion elements 32 are arrayed two-dimensionally. In other words, the plurality of scintillators 31 and the plurality of photoelectric conversion elements 32 are pixelated. The positions at which energy is emitted are scattering positions in the scatterer 140 and absorption positions in the absorber 160. When the detector 30 detects the position at which the gamma ray 20 emits energy in three dimensions, the plurality of scintillators 31 are arrayed three-dimensionally. Furthermore, the plurality of photoelectric conversion elements 32 are arrayed three-dimensionally.

[0031] The scintillator 31 is not particularly limited, but may be, for example, GAGG:Ce (Ce-doped Gd ３ (Al, Ga) ５ O １２ ), LYSO:Ce (Ce addition (Lu １－ｘ Y ｘ ) ２ SiO ５ ), and GSO(Gd ２ SiO ５ ) scintillator crystal.

[0032] The plurality of photoelectric conversion elements 32 are respectively attached to the plurality of scintillators 31. Specifically, each of the plurality of photoelectric conversion elements 32 may be attached to one scintillator 31, or two or more scintillators 31 may be attached to one photoelectric conversion element 32. That is, the photoelectric conversion elements 32 and the scintillators 31 may be paired one-to-one, or one photoelectric conversion element 32 (i.e., the photoelectric conversion element 32 of one pixel) may be provided across multiple scintillators 31 (i.e., scintillators 31 of multiple pixels). Each photoelectric conversion element 32 is configured to receive and detect (i.e., convert into an electrical signal) light output from the scintillator 31 paired with that photoelectric conversion element 32 or from two or more scintillators 31 provided for that photoelectric conversion element 32. By monitoring the signal strength (signal strength of each pixel) from the multiple photoelectric conversion elements 32 and performing a center of gravity calculation or the like, it is possible to identify which scintillator 31 the gamma ray 20 emitted energy from. In other words, it is possible to identify the position in the detector 30 at which the gamma ray 20 emitted energy. Based on the position of the photoelectric conversion element 32 that detected the light, it is possible to identify the position at which the energy was emitted as coordinates.

[0033] Furthermore, the photoelectric conversion element 32 can detect the intensity of light output from the scintillator 31, thereby detecting the magnitude of energy emitted from the gamma rays 20 to the scintillator 31. That is, the photoelectric conversion element 32 can output an electrical signal indicating the intensity of light output from the scintillator 31. The magnitude of energy emitted from the gamma rays 20 to the scintillator 31 corresponds to a first emission energy value in the scatterer 140 and a second emission energy value in the absorber 160.

[0034] Specifically, the photoelectric conversion element 32 outputs a pulse signal when it detects light. The magnitude of the amplitude of the pulse signal indicates the intensity of the detected light. Furthermore, by identifying the output timing of the pulse signal from the photoelectric conversion element 32, it is possible to identify the timing at which the gamma ray 20 emitted energy. As will be described in detail later, it is possible to associate scattering and absorption of the same gamma ray 20 (photons) based on the relationship between the timing at which the gamma ray 20 emitted energy in the scatterer 140 and the timing at which the gamma ray 20 emitted energy in the absorber 160.

[0035] However, the arrangement and relationship of the multiple scintillators 31 and the multiple photoelectric conversion elements 32 in the detector 30 are not limited to this example. Furthermore, the configurations of the scatterer 140 and the absorber 160 are not limited to this example. For example, the scatterer 140 may be a detector that converts the energy of gamma rays 20 into an electric signal using a semiconductor or the like. The absorber 160 may be a detector that converts the energy of gamma rays 20 into an electric signal using a semiconductor or the like. Furthermore, the scatterer 140 and the absorber 160 may have the same configuration as each other, or may have different configurations. For example, the scatterer 140 and the absorber 160 may be configured using detectors made of different materials.

[0036] FIG. 4 is a diagram illustrating the configuration of the measurement device 10 according to this embodiment. The measurement device 10 according to this embodiment further includes a first generation unit 170. The first generation unit 170 generates first distribution information regarding the incident direction of the gamma rays 20 to the attenuating body 120 using the scattering position information, absorption position information, first emission energy value, and second emission energy value of the gamma rays 20. The scattering position information is information indicating the scattering position of the gamma rays 20 in the scatterer 140. The absorption position information is information indicating the absorption position of the gamma rays 20 in the absorber 160. The first emission energy value is a value indicating the magnitude of energy emitted from the gamma rays 20 to the scatterer 140. The second emission energy value is a value indicating the magnitude of energy emitted from the gamma rays 20 to the absorber 160. The processing performed by the first generation unit 170 will be described in detail below.

[0037] 4 , the measurement device 10 further includes a first control unit 142 and a second control unit 162. The first control unit 142 is connected to the scatterer 140 and causes the scatterer 140 to detect energy emission from the gamma rays 20. The first control unit 142 may include, for example, a power supply circuit, a current-voltage conversion circuit, a filter circuit, an amplifier circuit, etc. When the scatterer 140 is realized as the detector 30, the first control unit 142 receives electrical signals output from a plurality of photoelectric conversion elements 32 in the scatterer 140. The first control unit 142 outputs a signal indicating the detection result of energy emission from the gamma rays 20 in the scatterer 140.

[0038] The second control unit 162 is connected to the absorber 160 and causes the absorber 160 to detect the emission of energy from the gamma rays 20. The second control unit 162 may include, for example, a power supply circuit, a current-voltage conversion circuit, a filter circuit, an amplifier circuit, etc. When the absorber 160 is realized as the detector 30, the second control unit 162 receives electrical signals output from the multiple photoelectric conversion elements 32 in the absorber 160. The second control unit 162 outputs a signal indicating the detection result of the energy emission from the gamma rays 20 in the absorber 160.

[0039] The hardware configuration of the first generating unit 170 will be described below. The first generating unit 170 may be realized by hardware that realizes the first generating unit 170 (e.g., a hardwired electronic circuit, etc.), or may be realized by a combination of hardware and software (e.g., a combination of an electronic circuit and a program that controls it, etc.). Below, a case where the first generating unit 170 of the measuring device 10 is realized by a combination of hardware and software will be further described.

[0040] FIG. 5 is a diagram illustrating a computer 1000 for realizing the first generation unit 170. The computer 1000 is any computer. For example, the computer 1000 is a system on chip (SoC), a personal computer (PC), a server machine, a tablet terminal, a smartphone, or the like. The computer 1000 may be a dedicated computer designed to realize the first generation unit 170, or may be a general-purpose computer. Furthermore, the first generation unit 170 may be realized by a single computer 1000 or by a combination of multiple computers 1000.

[0041] The computer 1000 includes a bus 1020, a processor 1040, a memory 1060, a storage device 1080, an input / output interface 1100, and a network interface 1120. The bus 1020 is a data transmission path through which the processor 1040, the memory 1060, the storage device 1080, the input / output interface 1100, and the network interface 1120 transmit and receive data to and from each other. However, the method of interconnecting the processor 1040 and other components is not limited to bus connection. The processor 1040 may be any of various processors, such as a central processing unit (CPU), a graphics processing unit (GPU), or a field-programmable gate array (FPGA). The memory 1060 is a main storage device implemented using a random access memory (RAM) or the like. The storage device 1080 is an auxiliary storage device implemented using a hard disk, a solid state drive (SSD), a memory card, a read-only memory (ROM), or the like.

[0042] The input / output interface 1100 is an interface for connecting the computer 1000 to an input / output device. For example, an input device such as a keyboard and an output device such as a display are connected to the input / output interface 1100. The input / output interface 1100 may be connected to the input device or output device via a wireless connection or a wired connection.

[0043] The network interface 1120 is an interface for connecting the computer 1000 to a network. This communication network may be, for example, a LAN (Local Area Network) or a WAN (Wide Area Network). The network interface 1120 may be connected to the network wirelessly or by wire.

[0044] The computer 1000 is connected to the first control unit 142 and the second control unit 162 via an input / output interface 1100 or a network interface 1120 .

[0045] The storage device 1080 stores a program module that implements the first generation unit 170. The processor 1040 reads this program module into the memory 1060 and executes it to implement the function corresponding to that program module.

[0046] The first generation unit 170 causes the measurement device 10 to function as a Compton camera. The principle of the imaging process performed by the first generation unit 170 will be described below.

[0047] 6 is a diagram illustrating the relationship between the attenuator 120, the scatterer 140, and the absorber 160 and the paths of the gamma rays 20 incident thereon. This diagram shows a phenomenon caused by a single-photon gamma ray 20. The gamma ray 20 incident on the attenuator 120 from the side opposite to the scatterer 140 passes through the attenuator 120 and arrives at a point P １ The light is scattered at point P １ The position of corresponds to the scattering position described above. The direction of travel of the gamma ray 20 changes due to scattering. The scattered gamma ray 20 then leaves the scatterer 140 and reaches a point P ２ At point P ２ It is absorbed at point P ２ The position of the point P corresponds to the absorption position described above. The x-axis, y-axis, and z-axis in FIG. １The xy plane is parallel to the main surface (incident surface 140a) of the scatterer 140. The attenuator 120, the scatterer 140, and the absorber 160 are arranged in the z direction. ２ From point P １ The direction toward the object is indicated by (θ, φ), and the scattering angle of Compton scattering is indicated by α.

[0048] The scatterer 140 causes Compton scattering of the gamma ray 20. １ and point P ２ When the position of the Compton cone 42 is specified, the gamma ray 20 will arrive at point P １ Then, candidates for the positions through which the gamma rays 20 have passed within the object plane 40 (referred to as "candidate positions") are found as the intersections of the conical surface of the Compton cone 42 and the object plane 40. As shown in FIG. 6 as an ellipse 44, a set of multiple candidate positions within the object plane 40 forms a perfect circle or an ellipse.

[0049] On the other hand, it is not possible to identify which of the multiple candidate positions within the target plane 40 the gamma ray 20 has actually passed through. In response to this, the first generation unit 170 according to this embodiment weights each of the multiple candidate positions based on the likelihood that the gamma ray 20 has passed through it.

[0050] FIG. 7 shows the point P １ 4 is a diagram illustrating an example of the positional relationship between the point P and the ellipse 44. As described above, the ellipse 44 is a set of multiple candidate positions. Ｃ is one of the candidate locations. In FIG. Ｃ is projected onto the xy plane. １ and point P Ｃ 8 is a diagram illustrating an example of the positional relationship between the point P １ is considered to be located within the top surface of the scatterer 140.

[0051] The gamma ray 20 is at point P Ｃ From point P １The gamma ray 20 passes through the attenuator 120 before reaching point P. Here, as described above, the attenuator 120 transmits the incident gamma ray 20 with a probability that depends on the angle of incidence. In detail, as described above, the larger the angle of incidence of the gamma ray 20 with respect to the incident surface 120a of the attenuator 120, the longer the length L that the gamma ray 20 passes through the attenuation section 122, and the lower the probability that the gamma ray 20 passes through the attenuator 120. That is, Ｃ From point P １ The longer the length L that the gamma ray 20 must pass through the attenuation section 122 before reaching point P １ In other words, it becomes difficult for the gamma ray 20 to reach the point P Ｃ From point P １ The longer the length L that must be passed through the attenuation section 122 before reaching the point P Ｃ Therefore, the first generating unit 170 can use the path length L to weight each of the multiple candidate positions based on the likelihood that the gamma ray 20 has passed through the point P Ｃ and point P １ It can be said that this is the length of the part of the straight line connecting these that overlaps with the attenuation portion 122.

[0052] The passing length L is the point P １ and point P Ｃ The path length L can be calculated using the positional relationship between the thickness T of the attenuation portion 122 in the z direction. １ Specifically, in the examples of FIGS. 7 and 8, the point P １ Point P with origin Ｃ The (x, y) coordinates of Ｃ , y Ｃ ) when point P Ｃ Projection point of onto the xy plane and point P １ The distance d between Ｃ ２ +y Ｃ ２ ) and the path length L is L = √(d ２ +T １ ２ ) is derived as follows.

[0053] 8 shows an example in which the incident surface 120a of the attenuator 120 is the target plane 40, but the target plane 40 is not limited to this example. The target plane 40 may be any plane outside the scatterer 140. "Outside the scatterer 140" means the side on which the attenuator 120 is located with the scatterer 140 as the reference.

[0054] Since one generatrix of the Compton cone 42 is one candidate path of the gamma ray 20, the same weight can be used on the same generatrix of the Compton cone 42. Therefore, even when the incident surface 120a of the attenuator 120 is not used as the target plane 40, the first generation unit 170 may specify the incident position on the incident surface 120a of the attenuator 120 of the path of the gamma ray 20 corresponding to each candidate position, and then calculate the weight in the same manner.

[0055] As described above, in FIG. １ is considered to be located within the top surface of the scatterer 140, but the processing example is not limited to this example. For example, １ may be considered to be located within the central plane in the thickness direction of the scatterer 140. In that case, in the derivation of the above-mentioned path length L, T １ Instead of (T １ +T ２ / 2) can be used. ２ is the thickness of the scatterer 140 in the z direction. １ may be considered to be located within the bottom surface of the scatterer 140. In that case, in the derivation of the path length L described above, T １ Instead of (T １ +T ２ ) can be used. １ If the three-dimensional coordinates of can be specified, the passing length L can be derived using the three-dimensional coordinates.

[0056] FIG. 9 is a flowchart illustrating the flow of processing performed by the first generation unit 170. The first generation unit 170 identifies a distribution of candidate positions through which the gamma ray 20 may have passed within the target plane 40 (S10). In S10, the first generation unit 170 can identify the distribution of the candidate positions using the scattering position information, absorption position information, first emission energy value, and second emission energy value of the gamma ray 20. The first generation unit 170 also derives a path length L for each of the multiple candidate positions (S20). In S20, the first generation unit 170 can derive the path length L based on the relationship between each of the multiple candidate positions included in the distribution and the scattering position of the gamma ray 20 in the scatterer 140. The first generation unit 170 also derives a weight w, which indicates the likelihood that the gamma ray 20 has passed through each of the multiple candidate positions, using the path length L (S30). Then, the first generating unit 170 generates first distribution information using the plurality of candidate positions and the weight w for each of the plurality of candidate positions (S40).

[0057] As will be described in detail below, the first generation unit 170 operates the measurement device 10 as a Compton camera. Therefore, the first generation unit 170 generates first distribution information using the path length L that the gamma rays 20 are assumed to have passed through the attenuation unit 122. Specifically, the first distribution information is generated that indicates not only the distribution of candidate positions but also the weight of each candidate position. This improves the measurement accuracy as a Compton camera.

[0058] The measurement method according to this embodiment and the processing performed by the first generator 170 are described in detail below. The first generator 170 can generate first distribution information based on the detection results of gamma rays 20 having energies of 200 kiloelectron volts (200 keV) or more and 10 megaelectron volts (10 MeV) or less (referred to as "high-energy band gamma rays 20"). In other words, the first generator 170 can generate first distribution information regarding the incident direction of high-energy band gamma rays 20 onto the attenuator 120. Gamma rays in this energy band pass through a parallel collimator and are therefore difficult to measure using a single photon emission computed tomography (SPECT) device. Therefore, the use of the measurement device 10 according to this embodiment is advantageous.

[0059] Prior to measurement, the attenuator 120, the scatterer 140, and the absorber 160 are arranged so that the attenuator 120 faces the measurement target region. That is, the attenuator 120 is located between the measurement target region and the scatterer 140. For example, the measurement target region is a region where a gamma ray source is estimated to be located. When the measurement device 10 is used for a nuclear medicine examination, the measurement target region is at least a part of the subject's body.

[0060] Furthermore, the user of the measurement device 10 performs an operation on the first generation unit 170 to identify the target plane 40. The user of the measurement device 10 may input information for identifying the target plane 40 to the first generation unit 170. Note that the operation for identifying the target plane 40 may be performed ex post after the measurement. In that case, for example, the first generation unit 170 may temporarily regard the incident surface 120a of the attenuation body 120 as the target plane 40 and perform the processing described below. Thereafter, the first generation unit 170 can generate output data for any target plane 40. The user can perform operations on the measurement device 10 using an input device such as a keyboard or mouse connected to the computer 1000. The same applies hereinafter.

[0061] During measurement, a plurality of gamma rays 20 are incident on the attenuator 120 from the measurement target area. The gamma rays 20 that pass through the attenuator 120 are scattered by the scatterer 140. Furthermore, the gamma rays 20 emitted from the scatterer 140 are absorbed by the absorber 160. Note that not all of the gamma rays 20 that enter the attenuator 120 necessarily pass through the attenuator 120. Some of the gamma rays 20 may disappear inside the attenuator 120.

[0062] The scatterer 140 detects the emission of energy from the gamma rays 20 to the scatterer 140. The first generation unit 170 acquires a signal indicating the detection result of the energy emission from the first control unit 142 connected to the scatterer 140. The first generation unit 170 processes this signal to identify, for each gamma ray 20, the scattering position, the first emission energy value, and the timing of the emission of energy from the gamma ray 20 to the scatterer 140. The first generation unit 170 identifies the coordinates of the scattering position as scattering position information.

[0063] For example, when the scatterer 140 is the detector 30 as described above, the first generating unit 170 detects pulses in the signal output from the first control unit 142. Position information (coordinates) for each photoelectric conversion element 32 is predetermined in the reference information, and the first generating unit 170 identifies the photoelectric conversion element 32 that is the output source of the pulse, and sets the position information corresponding to that photoelectric conversion element 32 in the reference information as scattering position information. The first generating unit 170 also identifies a first emitted energy value based on the magnitude of the amplitude of the detected pulse. The first generating unit 170 then identifies the energy emission timing based on the timing of the detected pulse.

[0064] The absorber 160 detects the emission of energy from the gamma rays 20 to the absorber 160. The first generation unit 170 acquires a signal indicating the detection result of the energy emission from the second control unit 162 connected to the absorber 160. The first generation unit 170 processes this signal to identify, for each gamma ray 20, the absorption position, the second emission energy value, and the timing of the emission of energy from the gamma ray 20 to the absorber 160. The first generation unit 170 identifies the coordinates of the absorption position as absorption position information.

[0065] For example, when the absorber 160 is the detector 30 as described above, the first generation unit 170 detects a pulse in the signal output from the second control unit 162. Position information (coordinates) for each photoelectric conversion element 32 is predetermined in the reference information, and the first generation unit 170 identifies the photoelectric conversion element 32 that is the output source of the pulse, and sets the position information corresponding to that photoelectric conversion element 32 in the reference information as absorption position information. The first generation unit 170 also identifies a second emitted energy value based on the magnitude of the amplitude of the detected pulse. The first generation unit 170 then identifies the energy emission timing based on the timing of the detected pulse.

[0066] Note that, instead of the first generating unit 170 identifying the scattering position information, the absorption position information, the first emission energy value, the second emission energy value, the energy emission timing in the scatterer 140, and the energy emission timing in the absorber 160, at least some of this information may be generated (identified) in another device. Then, the first generating unit 170 may acquire the information generated in the other device.

[0067] Next, the first generation unit 170 associates the scattering position information, absorption position information, first emission energy value, and second emission energy value with each other based on the energy emission timing in the scatterer 140 and the energy emission timing in the absorber 160. Specifically, if the difference between the energy emission timing in the scatterer 140 and the energy emission timing in the absorber 160 is equal to or less than a predetermined value Δt, the first generation unit 170 considers that these energy emissions are caused by the same gamma ray 20. That is, the first generation unit 170 associates the scattering position information, absorption position information, first emission energy value, and second emission energy value obtained by detecting these energy emissions with each other. Here, the predetermined value Δt is, for example, equal to or less than 1 microsecond (1 μs).

[0068] The first generating unit 170 then uses the scattering position information, absorption position information, first emission energy value, and second emission energy value that are associated with each other to identify the distribution of candidate positions as follows (S10).

[0069] The first generator 170 uses the scattering position information and the absorption position information to derive a unit vector (θ, φ) of the axis of the Compton cone 42. The unit vector (θ, φ) is obtained as a unit vector (polar coordinates) in the direction from the absorption position to the scattering position.

[0070] The first generating unit 170 also calculates the value of cos α using the following equation (1): m ｅ c ２ is the rest energy of the electron, E １ is the first released energy value, E ２ is the second emission energy value, and α is the scattering angle of Compton scattering.

[0071]

[0072] Here, the scattering position (point P １ The equation of a conical surface (Compton cone) with vertices at points P and P is expressed by the following equation (2). Point P is a point on the conical surface. Vector v is a unit vector of the axis of the cone.

[0073]

[0074] Furthermore, when the unit vector (θ, φ) is converted into orthogonal coordinates, the following equation (3) holds.

[0075]

[0076] Point P １ is the origin, and the z coordinate of the target plane 40 is z ｔ When the following equation (4) in which:

[0077]

[0078] The first generation unit 170 generates a point (x, y, z) where the difference between the left and right sides of the formula (5) is smaller than a predetermined threshold. ｔ ) is identified as a point on the curve where the cone intersects with the target plane 40, i.e., as a candidate position. A plurality of such candidate positions are identified.

[0079] In this way, the first generating unit 170 can identify the positions of a plurality of candidate positions. That is, the first generating unit 170 can identify the distribution of the candidate positions.

[0080] Next, the first generating unit 170 derives the above-mentioned path length L for each of the plurality of candidate positions (S20). １ ) and the candidate position (point P Ｃ The transmission length L can be geometrically derived using at least the coordinates of the attenuation body 120 and information indicating the area occupied by the attenuation body 120. The information indicating the area occupied by the attenuation body 120 is, for example, the thickness T １ The first generation unit 170 further calculates the thickness T ２ The path length L may be derived using the following equation. An example of the method of derivation is as described above with reference to FIGS.

[0081] Then, the first generator 170 derives a weight w for each of the plurality of candidate positions using the derived passage length L (S30). The likelihood that the gamma ray 20 will pass through the passage thickness L is calculated using the linear attenuation coefficient μ as follows: －μＬ The first generation unit 170 is expressed by, for example, e －μＬ The first generation unit 170 uses e －μＬ The weight w may be a value obtained by further multiplying e by some coefficient or the like. e is a natural number. μ is a coefficient that depends on the material that constitutes the attenuation portion 122 and the energy of the gamma ray 20. The first generation unit 170 can use a predetermined value of μ to calculate the weight w.

[0082] As another example, weight reference information (e.g., a table) may be prepared in advance that indicates the relationship between the positional relationship between the scattering positions and the candidate positions and the weight w. In this case, after identifying multiple candidate positions in S10, the first generator 170 may identify the weight w using the scattering position information, the coordinates of the candidate positions, and the weight reference information, instead of deriving the path length L.

[0083] The first generation unit 170 generates information in which the calculated weight w is associated with each of the multiple candidate positions as first distribution information (S40). The first distribution information is, for example, information in which the weight w is associated with each of multiple position coordinates (i.e., the position coordinates of the multiple candidate positions).

[0084] The first generation unit 170 may further generate first distribution information for each of the plurality of gamma rays 20 that pass through the attenuator 120. Then, the generated plurality of pieces of first distribution information may be accumulated to generate cumulative distribution information. In this case, a weight w is added up for each coordinate in the target plane 40. The number of gamma rays 20 for which information is accumulated is not particularly limited, but may be, for example, 1000 or more.

[0085] The first generating unit 170 can output at least one of the first distribution information and the cumulative distribution information as output data. The first generating unit 170 can output the output data in the form of a table or the like, or as an image. In the image, the distribution can be represented by a color or brightness corresponding to the weight w or the cumulative value of the weight w. The first generating unit 170 can also output the output data by superimposing it on an image of the measurement target area. The first generating unit 170 can display the output data on a display connected to the computer 1000 that implements the first generating unit 170, or can output the output data to be stored in the storage device 1080 of the computer 1000 that implements the first generating unit 170 or in an external storage device of the measurement device 10.

[0086] 10 is a diagram illustrating an example of an image showing the first distribution information generated by the first generator 170. An ellipse representing a set of multiple candidate positions is displayed, and the magnitude of the weight w, i.e., the likelihood, for each candidate position is indicated by color. This makes it possible to distinguish the magnitude of the weight w, i.e., the likelihood, for multiple candidate positions.

[0087] FIG. 11 is a diagram illustrating an image of cumulative distribution information according to a reference example. FIG. 12 is a diagram illustrating an image of cumulative distribution information according to this embodiment. The reference example of FIG. 11 shows an example in which candidate positions are not weighted, and all of the multiple candidate positions (i.e., ellipses) for each gamma ray 20 are uniformly displayed. In this case, unless information about many gamma rays 20 is accumulated, it is not possible to determine the actual location of the gamma ray source (indicated by a star in FIG. 11 ). On the other hand, the cumulative distribution information according to this embodiment is weighted based on the likelihood, so that the most likely location of the gamma ray source (indicated by a star in FIG. 12 ) can be determined even from information about a smaller number of gamma rays 20.

[0088] Next, the operation and effect of this embodiment will be described. According to this embodiment, by using the attenuator 120 that transmits the incident gamma rays 20 with a probability according to the angle of incidence, it becomes possible to weight the candidate positions, and it is possible to detect the direction from which the gamma rays have arrived with a simple configuration and with high accuracy.

[0089] 13 is a perspective view illustrating an attenuation body 120 according to a second embodiment. The measurement device 10 and the measurement method according to this embodiment are the same as the measurement device 10 and the measurement method according to the first embodiment, except for the points described below.

[0090] The attenuator 120 according to this embodiment is a parallel collimator. In the example of FIG. 13 , the attenuator 120 has a plurality of walls of attenuating sections 122. The thickness of the walls of the attenuator sections 122 is, for example, 0.1 mm or more and 3 mm or less. In the attenuator 120, the walls of the attenuator sections 122 are arranged in a lattice pattern. In other words, in the attenuator 120, the attenuator sections 122 are arranged, for example, to form a plurality of rectangles. The insides of these rectangles may be empty. It can be said that the attenuator 120 is provided with a plurality of through holes. The shape of the through holes (i.e., the shape of the cross section perpendicular to the axis of the through holes) is not particularly limited, and may be, for example, a polygon such as a triangle, a rectangle, or a hexagon, a circle, or an ellipse.

[0091] Regarding gamma rays 20 in the low energy band described below, only the gamma rays 20 that pass through the through-holes pass through the attenuator 120 without entering the attenuator section 122. On the other hand, gamma rays 20 that enter the attenuator section 122 are absorbed by the attenuator section 122 and do not pass through the attenuator 120. Therefore, only the attenuator 120 that enters the attenuator 120 at a position and angle that allows it to pass through the through-holes reaches the scatterer 140. On the other hand, regarding gamma rays 20 in the high energy band described above, the attenuator 120 transmits the gamma rays 20 with a probability that depends on the angle of incidence, as explained in the first embodiment.

[0092] In the attenuator 120 according to this embodiment, the distance between the walls of the attenuation sections 122 facing each other is, for example, 0.5 mm or more and 5 mm or less. The thickness of the attenuator 120 according to this embodiment in the direction perpendicular to the incident surface 120 a is, for example, 3 mm or more and 15 mm or less. Note that the positional relationship between the walls of the attenuation sections 122 in the attenuator 120 and the scintillator 31 and photoelectric conversion element 32 in the detector 30 is not particularly limited.

[0093] According to this embodiment, the attenuator 120 is a parallel collimator, so that the measurement apparatus 10 can also function as a SPECT apparatus.

[0094] 14 is a diagram illustrating an example of the functional configuration of the measurement device 10 according to this embodiment. The measurement device 10 according to this embodiment further includes a second generation unit 180. The second generation unit 180 generates arrival information regarding the origin of the gamma rays 20, using absorption position information in the scatterer 140, of the gamma rays 20 absorbed by the scatterer 140. The second generation unit 180 causes the measurement device 10 to function as a SPECT device.

[0095] The hardware configuration of the computer that realizes the second generation unit 180 is, for example, shown in Fig. 5 , similar to the first generation unit 170. However, a program module that realizes the functions of the second generation unit 180 is stored in a storage device 1080 of the computer 1000 that realizes the second generation unit 180. The computer 1000 that realizes the second generation unit 180 may also serve as the computer 1000 that realizes the first generation unit 170, or may be provided separately.

[0096] The second generation unit 180 can generate arrival information based on the detection results of gamma rays 20 having an energy of, for example, 20 kiloelectron volts (20 keV) or more and 200 kiloelectron volts (200 keV) or less (referred to as "low-energy band gamma rays 20"). In other words, the second generation unit 180 can generate arrival information regarding where the low-energy band gamma rays 20 have come from. In other words, the arrival information can be said to be information regarding gamma rays 20 with lower energy than the first distribution information.

[0097] In this embodiment, the attenuator 120 is a parallel collimator, and therefore it is possible to block gamma rays 20 in the low energy band as described above that are incident obliquely onto the attenuator 120. Therefore, only gamma rays 20 that are incident on the incident surface 120a of the attenuator 120 from approximately the normal direction thereof pass through the attenuator 120 and enter the scatterer 140. The gamma rays 20 that are incident on the scatterer 140 are then absorbed by the scatterer 140. In other words, the scatterer 140 can also function as an absorber. The gamma rays 20 that are incident on the scatterer 140 do not pass through the scatterer 140, i.e., are not emitted from the scatterer 140.

[0098] The measurement flow when the measurement device 10 functions as a SPECT device will be described in detail below. Prior to measurement, the attenuator 120, the scatterer 140, and the absorber 160 are arranged so that the attenuator 120 faces the measurement target region. That is, the attenuator 120 is located between the measurement target region and the scatterer 140. For example, the measurement target region is a region where a gamma ray source is estimated to be located. When the measurement device 10 is used for nuclear medicine examination, the measurement target region is at least a part of the subject's body.

[0099] During measurement, a plurality of gamma rays 20 are incident on the attenuator 120 from the measurement target area. The gamma rays 20 that pass through the attenuator 120 are absorbed by the scatterer 140. As described above, not all of the gamma rays 20 that are incident on the attenuator 120 necessarily pass through the attenuator 120. The gamma rays 20 that are incident obliquely on the attenuator 120 disappear inside the attenuator 120.

[0100] When the gamma rays 20 are absorbed by the scatterer 140, the scatterer 140 detects the emission of energy from the gamma rays 20 to the scatterer 140. The second generation unit 180 acquires a signal indicating the detection result of the energy emission from the first control unit 142 connected to the scatterer 140. The second generation unit 180 processes this signal to identify absorption position information in the scatterer-attenuating body 120 for each gamma ray 20. Specifically, the second generation unit 180 can identify the coordinates of the absorption position in the scatterer 140 as absorption position information in the scatterer 140, in the same way that the first generation unit 170 identifies scattering position information.

[0101] The second generating unit 180 further specifies the magnitude of energy (i.e., absorbed energy) emitted from the gamma ray 20 to the scatterer 140 when the gamma ray 20 is absorbed by the scatterer 140, in the same way as the first generating unit 170 specifies the first energy value. The second generating unit 180 associates this energy value with the absorption position information.

[0102] Note that, instead of the second generating unit 180 specifying the absorption position information and the magnitude of the absorbed energy when the gamma rays 20 are absorbed by the scatterer 140, at least one of these pieces of information may be generated (specified) in another device. Then, the second generating unit 180 may acquire the information generated in the other device.

[0103] FIG. 15 is a flowchart illustrating the flow of processing performed by the second generating unit 180.

[0104] The second generating unit 180 generates arrival information including absorption position information when the gamma rays 20 are absorbed by the scatterer 140 (S60). The second generating unit 180 can use this absorption position information itself as the arrival information.

[0105] Alternatively, the second generation unit 180 may determine whether the energy absorbed by the scatterer 140 is within a predetermined target energy band. Here, the target energy band can be determined according to the energy band of the gamma rays 20 for which information about where the gamma rays 20 originate is desired to be obtained. If the energy absorbed by the scatterer 140 is within the target energy band, the second generation unit 180 regards the absorption position information associated with that energy as arrival information. On the other hand, if the energy absorbed by the scatterer 140 is not within the target energy band, the second generation unit 180 does not regard the absorption position information associated with that energy as arrival information. In this way, information about the gamma rays 20 in the desired energy band can be obtained.

[0106] The second generation unit 180 may further generate arrival information for each of the multiple gamma rays 20 that pass through the attenuator 120. Then, the multiple pieces of arrival information generated may be accumulated to generate cumulative arrival information. Specifically, the second generation unit 180 adds up the number of detected gamma rays 20 (number of pieces of arrival information) for each coordinate. The cumulative arrival information provides a distribution of where the gamma rays have come from. The number of gamma rays 20 for which information is accumulated is not particularly limited, but may be, for example, 1000 or more.

[0107] The second generating unit 180 can output at least one of the arrival information and the cumulative arrival information as output data. The second generating unit 180 may output the output data in the form of a table or the like, or as an image. In the image, the distribution may be shown using colors or brightness corresponding to the cumulative number of gamma rays 20. The second generating unit 180 may also output the output data superimposed on an image of the measurement target area. The second generating unit 180 may display the output data on a display connected to the computer 1000 that implements the second generating unit 180, or may output the output data to be stored in the storage device 1080 of the computer 1000 that implements the second generating unit 180 or in a storage device external to the measurement device 10.

[0108] In the measurement device 10 according to this embodiment, it is possible to switch between causing the measurement device 10 to function as a Compton camera and as a SPECT device. That is, in the measurement device 10 according to this embodiment, it is possible to switch between causing the first generation unit 170 to perform processing to generate first distribution information and causing the second generation unit 180 to perform processing to generate arrival information. For example, a user can perform a predetermined operation on the measurement device 10 to switch between generating the first distribution information and generating arrival information.

[0109] The processing performed by the first generator 170 according to this embodiment will be described below. The processing performed by the first generator 170 according to this embodiment is the same as the processing performed by the first generator 170 according to the first embodiment, except for the method of deriving the path length L.

[0110] FIG. 16 shows the attenuation section 122 according to this embodiment and the scattering position (point P １ ), and the candidate position (point P Ｃ 16 is a diagram showing the relationship between the ellipse 44 and the point P Ｃ is projected onto the xy plane. In FIG. 16, the wall of the attenuation section 122 is shown by vertical and horizontal straight lines. A set of multiple candidate positions is shown by an ellipse, and the point P Ｃ is one candidate location.

[0111] The first generation unit 170 according to this embodiment derives the path length L of the gamma ray 20 passing through the attenuation unit 122 based on the scattering position, the candidate position, and the structure of the attenuation unit 122. Information indicating the structure of the attenuation unit 122 is determined in advance. The information indicating the structure of the attenuation unit 122 includes information indicating the positions (e.g., spacing) of the multiple walls of the attenuation unit 122 and the thickness of the walls. In this embodiment, the first generation unit 170 derives the number of walls through which the gamma ray 20 passes based on the scattering position, the candidate position, and the positions of the multiple walls of the attenuation unit 122. The first generation unit 170 can then derive the path length L by multiplying the wall thickness of the attenuation unit 122 by the number of walls through which the gamma ray 20 passes. In the example of FIG. 16 , the gamma ray 20 passes through the point P Ｃ From point P １On the way to the candidate position, the gamma ray 20 passes through one wall in the vertical direction and two walls in the horizontal direction. Therefore, the number of walls through which the gamma ray 20 passes is three. The first generator 170 sets the value obtained by multiplying the thickness of the wall of the attenuation section 122 by 3 as the pass length L of the candidate position. The first generator 170 derives the weight w using the pass length L, as in the first embodiment.

[0112] In this embodiment, as another example, weight reference information (for example, a table) may be prepared in advance that indicates the relationship between the positional relationship between the scattering positions and the candidate positions and the weight w. In this case, after identifying multiple candidate positions in S10, the first generator 170 may identify the weight w using the scattering position information, the coordinates of the candidate positions, and the weight reference information, instead of deriving the path length L.

[0113] Next, the operation and effect of this embodiment will be described. In this embodiment, the same operation and effect as in the first embodiment can be obtained. In addition, according to this embodiment, since the attenuator 120 is a parallel collimator, the measurement device 10 can also function as a SPECT device capable of measuring gamma rays 20 in a low energy band.

[0114] The present embodiment will be described in detail below with reference to examples, but the present embodiment is not limited to the descriptions of these examples.

[0115] Example 1 In Example 1, measurements were performed using the measurement method according to the second embodiment.

[0116] FIG. 17 is a diagram showing the measurement configuration according to Example 1. A scatterer 140 and an absorber 160 were placed inside a housing 91, and an attenuator 120 was placed on top of the housing 91. That is, a plate (made of resin) constituting the upper surface of the housing 91 was interposed between the attenuator 120 and the scatterer 140. The distance between the attenuator 120 and the scatterer 140 was approximately 4 mm. As the attenuator 120, a parallel collimator (made of tungsten, 5 mm thick in the Z direction, 1.5 mm thick walls arranged in a lattice pattern, and 0.5 mm spacing between the walls arranged in a lattice pattern) as shown in FIG. 13 was used. As the scatterer 140 and the absorber 160, the detector 30 described in the first embodiment was used. As the scintillator 31, a GAGG:Ce scintillator crystal was used.

[0117] A gamma ray source 92 was placed on the attenuator 120. The gamma ray source 92 was １３３ Ba (356 keV) was used. The distance between the center of the attenuator 120 and the center of the gamma ray source 92 was 2 cm.

[0118] The cumulative distribution information shown in Fig. 18 was obtained by processing performed by the first generation unit 170 according to the second embodiment. The imaging time when the cumulative distribution information shown in Fig. 18 was obtained was 10 minutes, and the number of detected events (number of gamma rays) was 12,000. As shown in this figure, the position of the gamma ray source 92 was detected by the measurement device 10. Note that Fig. 18 shows an XY plane with the plane including the bottom surface of the gamma ray source 92 as the target plane, and the center of the attenuation body 120 as the origin. The same applies to Figs. 19, 20, 22, 23, and 24 below.

[0119] (Comparative Example 1) Measurement was performed in the same manner as in Example 1, except that the attenuator 120 was not used and weighting was not performed for each of the multiple candidate positions. That is, the gamma ray source 92 was placed directly on the housing 91, and the multiple resulting candidate positions were treated uniformly. The resulting distribution data for the multiple candidate gamma ray positions was accumulated to obtain Figure 19. The imaging time when the cumulative distribution information shown in Figure 19 was obtained was 10 minutes, and the number of detected events (number of gamma rays) was 24,000.

[0120] Fig. 20 shows profiles of the cumulative distribution information shown in Fig. 18 and Fig. 19. The pixel values ​​in the range from Y = -1.5 mm to Y = 6 mm of the images shown in Fig. 18 and Fig. 19 were integrated for each X coordinate, and the values ​​obtained were plotted in Fig. 20. Fig. 20 confirms that Example 1 produced a sharper peak than Comparative Example 1, and that measurements were made with a higher S / N ratio.

[0121] Example 2 Measurement was carried out in the same manner as in Example 1, except that two gamma ray sources 92 were arranged on the attenuation body 120 .

[0122] Fig. 21 is a diagram showing the measurement configuration according to Example 2. The center-to-center distance between the two gamma ray sources 92 was 5 cm. The center between the two gamma ray sources 92 was aligned with the center of the attenuator 120. The gamma ray source 92 on the right in Fig. 21 had a gamma ray intensity about twice that of the gamma ray source 92 on the left.

[0123] The cumulative distribution information shown in Fig. 22 was obtained by processing performed by the first generation unit 170 according to the second embodiment. The imaging time when the cumulative distribution information shown in Fig. 22 was obtained was 10 minutes, and the number of detected events (number of gamma rays) was 11,000. As shown in this figure, the positions of two gamma ray sources 92 were detected by the measurement device 10.

[0124] Comparative Example 2 Measurement was performed in the same manner as in Example 2, except that the attenuator 120 was not used and weighting was not performed for each of the multiple candidate positions. The gamma ray sources used and their arrangement were the same as in Example 2.

[0125] As in Comparative Example 1, the obtained multiple position candidates were treated uniformly to obtain the cumulative distribution information shown in Fig. 23. When the cumulative distribution information shown in Fig. 23 was obtained, the imaging time was 10 minutes, and the number of detected events (number of gamma rays) was 20,000.

[0126] Figure 24 shows profiles of the cumulative distribution information shown in Figures 22 and 23. The pixel values ​​within the range of Y = -1.5 mm to Y = 6 mm of the images shown in Figures 22 and 23 were integrated for each X coordinate, and the values ​​obtained were plotted in Figure 24. It was confirmed from Figure 24 that the two peaks in Example 2 were more clearly separated than in Comparative Example 2, and measurements were made with a higher S / N ratio.

[0127] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations may be adopted. For example, although the sequence diagrams and flowcharts used in the above description show multiple steps (processes) in order, the order of execution of the steps in each embodiment is not limited to the order shown. In each embodiment, the order of the steps shown in the drawings may be changed to the extent that the content is not affected. Furthermore, the above-described embodiments may be combined to the extent that the content is not contradictory.

[0128] REFERENCE SIGNS LIST 10 Measuring device 20 Gamma rays 30 Detector 31 Scintillator 32 Photoelectric conversion element 40 Target plane 42 Compton cone 44 Ellipse 91 Housing 92 Gamma ray source 120 Attenuator 122 Attenuation section 140 Scatterer 142 First control section 160 Absorber 162 Second control section 170 First generation section 180 Second generation section 1000 Computer 1020 Bus 1040 Processor 1060 Memory 1080 Storage device 1100 Input / output interface 1120 Network interface

Claims

1. A measuring device comprising: an attenuator that transmits incident gamma rays with a probability according to the incident angle; a scatterer that scatters at least a part of the gamma rays transmitted through the attenuator; and an absorber that absorbs at least a part of the gamma rays scattered by the scatterer.

2. The measuring device according to claim 1, further comprising a first generation unit that generates first distribution information regarding the incident direction of the gamma rays to the attenuator by using the scattering position information of the gamma rays at the scatterer, the absorption position information of the gamma rays at the absorber, the first emission energy value of the gamma rays from the scatterer, and the second emission energy value of the gamma rays from the absorber.

3. The measuring device according to claim 2, wherein the attenuator has an attenuation part that attenuates the number of gamma rays, and the first generation unit generates the first distribution information by further using the passing length assumed that the gamma rays have passed through the attenuation part.

4. The measuring device according to claim 3, wherein the first generation unit: identifies the distribution of candidate positions where the gamma rays may have passed within the target plane by using the scattering position information, the absorption position information, the first emission energy value, and the second emission energy value of the gamma rays; derives the passing length for each of the plurality of candidate positions included in the distribution based on the relationship between each of the plurality of candidate positions included in the distribution and the scattering position of the gamma rays at the scatterer; derives a weight indicating the likelihood that the gamma rays have passed through each of the plurality of candidate positions by using the passing length; and generates the first distribution information by using the plurality of candidate positions and the weights for each of the plurality of candidate positions.

5. The measuring device according to any one of claims 1 to 4, wherein the attenuator is a parallel collimator.

6. The measuring device according to claim 5, further comprising a second generation unit that generates arrival information regarding where the gamma rays have arrived by using the absorption position information of the gamma rays absorbed by the scatterer at the scatterer.

7. The measuring device according to any one of claims 1 to 6, wherein the distance between the attenuator and the scatterer is 5 mm or less.

8. A measurement method in which gamma rays are made incident on an attenuator that transmits the incident gamma rays with a probability according to the incident angle, at least a part of the gamma rays transmitted through the attenuator is scattered by a scatterer, and at least a part of the gamma rays scattered by the scatterer is absorbed by an absorber.

Images