WO2025109671A1 - Measurement device and measurement method - Google Patents

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

The present invention relates to a measuring device and a measuring method.

Compton cameras are devices that detect the direction from which gamma rays come. Compton cameras are used, for example, in the fields of physics, astronomy, medicine, and the environment.

Non-Patent Document 1 describes a technology that simultaneously images the distribution of two types of radiopharmaceuticals (SPECT and PET drugs) inside the human body using a single Compton camera.

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

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, 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

However, in the technology of Non-Patent Document 1, the distribution of the two drugs was imaged only by a Compton camera. As a result, the resolution of both drugs was poorer than that of normal SPECT and PET devices, and there was a problem that it was not suitable for practical use. In addition, in the technology of Non-Patent Document 2, it was difficult to image the general-purpose ^99m Tc as a SPECT drug, so a special drug ¹¹¹ In that emits multiple photons and gamma rays with higher energy than ^99m Tc was used.

The present invention provides a radiation measuring device that is highly versatile and accurate.

According to one embodiment of the present invention, the following measurement device and measurement method are provided.

1. An attenuator that transmits incident gamma rays with a probability that depends on the angle of incidence;
a scatterer that scatters at least a portion of the gamma rays that have passed through the attenuator;
and an absorber that absorbs at least a portion of the gamma rays scattered by the scatterer.
2. In the measuring device according to 1.,
The measurement device further includes a first generation unit that generates first distribution information regarding the incident direction of the gamma ray into the attenuator using scattering position information of the gamma ray in the scatterer, absorption position information of the gamma ray in the absorber, a first emission energy value from the gamma ray to the scatterer, and a second emission energy value from the gamma ray to the absorber.
3. In the measuring device according to 2.,
The attenuator has an attenuation portion that attenuates the number of gamma rays,
A measurement device in which the first generation unit generates the first distribution information by further using a path length assumed to be taken by a gamma ray passing through the attenuation unit.
4. In the measuring device according to 3.,
The first generation unit is
Identifying a distribution of candidate positions through which the gamma ray may have passed within the target 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;
deriving the path length for each of a plurality of candidate positions based on a relationship between each of the candidate positions included in the distribution and a scattering position of the gamma ray in the scatterer;
deriving a weight indicating a likelihood that the gamma ray has passed through each of the plurality of candidate positions using the path length;
A measurement device that generates the first distribution information using the plurality of candidate positions and the weights for each of the plurality of candidate positions.
5. The measurement device according to any one of 1 to 4,
The measuring device, wherein the attenuator is a parallel collimator.
6. In the measuring device according to 5.,
The measuring device further includes a second generating unit that generates arrival information regarding where the gamma rays came from, using absorption position information in the scatterer of the gamma rays absorbed in the scatterer.
7. The measurement device according to any one of 1. to 6.,
A measuring device, wherein the distance between the attenuator and the scatterer is 5 mm or less.
8. Gamma rays are made incident on an attenuating body that transmits the incident gamma rays with a probability according to the angle of incidence,
At least a portion of the gamma rays that have passed through the attenuator is scattered by a scatterer;
A measuring method in which at least a portion of the gamma rays scattered by the scatterer is absorbed by an absorber.

The present invention provides a radiation measuring device that is highly versatile and accurate.

FIG. 1 is a diagram illustrating a configuration of a measurement apparatus according to a first embodiment. 3A to 3C are diagrams illustrating an example of an attenuation body according to the first embodiment. FIG. 13 is a diagram illustrating a configuration of a detector for realizing a scatterer and an absorber. FIG. 1 is a diagram illustrating a configuration of a measurement apparatus according to a first embodiment. FIG. 11 is a diagram illustrating a computer for implementing a first generation unit. 1 is a diagram illustrating an example of the relationship between an attenuator, a scatterer, and an absorber and gamma rays incident thereon; 13 is a diagram illustrating an example of the positional relationship between a point _P1 and an ellipse. FIG. 1 is a diagram illustrating an example of the positional relationship between points _P1 and _Pc . 11 is a flowchart illustrating a process flow performed by a first generation unit. 11 is a diagram illustrating an example of an image showing first distribution information generated by a first generator. FIG. FIG. 13 is a diagram illustrating an example of cumulative distribution information according to a reference example. FIG. 4 is a diagram illustrating an example of cumulative distribution information according to the first embodiment; 13 is a perspective view illustrating an attenuation body according to a second embodiment. FIG. FIG. 11 is a diagram illustrating a functional configuration of a measurement device according to a second embodiment. 11 is a flowchart illustrating a flow of a process performed by a second generation unit. FIG. 13 is a diagram showing the relationship between an attenuation section according to the second embodiment, a scattering position (point P ₁ ), and a candidate position (point P _C ). FIG. 1 is a diagram showing a measurement configuration according to a first embodiment. FIG. 13 is a diagram showing cumulative distribution information according to the first embodiment. FIG. 13 is a diagram showing cumulative distribution information according to Comparative Example 1. 20 is a line profile of the cumulative distribution information shown in each of FIGS. 18 and 19. FIG. 11 is a diagram showing a measurement configuration according to Example 2. FIG. 13 is a diagram showing cumulative distribution information according to the second embodiment. FIG. 11 is a diagram showing cumulative distribution information according to Comparative Example 2. 24 is a line profile of the cumulative distribution information shown in each of FIG. 22 and FIG. 23.

Below, an embodiment of the present invention will be described with reference to the drawings. Note that in all drawings, similar components are given similar reference numerals and descriptions will be omitted where appropriate.

First Embodiment
FIG. 1 is a diagram illustrating a configuration of a measuring device 10 according to a first embodiment. In FIG. 1, a gamma ray source is indicated by a black circle. The measuring 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.

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.

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

The measuring device 10 and measuring method according to this embodiment use an attenuator 120, making it possible to measure with high accuracy the direction from which the gamma rays 20 have arrived. The measuring device 10 and measuring method according to this embodiment are described in detail below.

FIG. 2 is a diagram showing an example of an 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 in the 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.

The attenuator 120 has an attenuation section 122 that attenuates the number of gamma rays 20. That is, when multiple gamma rays 20 are incident on 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 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 includes, for example, at least one of tungsten, lead, tin, and copper. Alternatively, the attenuation section 122 may include an alloy including at least one of tungsten, lead, tin, and copper. In the example of FIG. 2, the attenuation section 122 is a flat metal plate. Also, 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.

The probability that the gamma ray 20 will pass through the attenuation section 122 decreases as the length L through which the gamma ray 20 passes through the attenuation section 122 increases. In other words, the greater the angle of incidence of the gamma ray 20 with respect to the incidence surface 120a of the attenuation body 120, the lower the probability that the gamma ray 20 will pass through the attenuation body 120 without being absorbed by the attenuation section 122.

In the example of FIG. 2, the attenuator 120 is generally flat. The incident surface 120a of the attenuator 120 is one of the main surfaces of the attenuator 120. The exit surface 120b of the attenuator 120 is the other of the main surfaces of the attenuator 120, and is the surface opposite 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.

The incident angle of 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 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.

The scatterer 140 scatters the gamma rays 20 that are incident on the scatterer 140. That is, the exit angle of the gamma rays 20 from the scatterer 140 may differ from the angle of incidence of the gamma rays 20 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.

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, and the higher the measurement accuracy of the measuring 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, other members that do not affect the gamma rays 20 may be interposed between the attenuator 120 and the scatterer 140.

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 (called 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 (called 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.

The absorber 160 absorbs the gamma rays 20 that are incident on the absorber 160. In other words, 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 is generally flat. The incident surface 160a of the absorber 160 is one of the main surfaces of the absorber 160.

The exit surface 140b of the scatterer 140 faces the entrance surface 160a of the absorber 160. The exit surface 140b of the scatterer 140 is parallel to the entrance 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 separated from each other. When the scatterer 140 and the absorber 160 are in contact with each other, high sensitivity is obtained but the resolution is reduced. Conversely, by widening the distance between the scatterer 140 and the absorber 160, the resolution can be increased but the sensitivity is reduced and the field of view is narrowed. 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.

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 (called the "second emitted energy value"). The absorber 160 also has a function of detecting the position where the gamma rays 20 are absorbed within the absorber 160 (called 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 a detector 30, which will be described in detail later using FIG. 3.

In the measuring device 10, the attenuator 120, the scatterer 140, and the absorber 160 are arranged in this order. The relative positions of the attenuator 120, the scatterer 140, and the absorber 160 are fixed relative to one another.

Figure 3 is a diagram illustrating the configuration of a detector 30 for realizing a scatterer 140 and an 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 it. 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, PMTs (photomultiplier tubes), photodiodes, or optical elements with internal amplification functions (avalanche photodiodes or silicon photomultipliers). The array of photoelectric conversion elements 32 is, for example, arrayed PMTs, arrayed photodiodes, arrayed avalanche photodiodes, or arrayed silicon photomultipliers. An example of a silicon photomultiplier that can be arrayed is a Multi-Pixel Photon Counter (MPPC).

In the example of FIG. 3, the detector 30 detects the position where the gamma ray 20 emits energy in two dimensions. That is, the multiple scintillators 31 are arrayed two-dimensionally. Also, the multiple photoelectric conversion elements 32 are arrayed two-dimensionally. In other words, the multiple scintillators 31 and the multiple photoelectric conversion elements 32 are pixelated. The positions where energy is emitted are the scattering positions in the scatterer 140 and the absorption positions in the absorber 160. When the detector 30 detects the positions where the gamma ray 20 emits energy in three dimensions, the multiple scintillators 31 are arrayed three-dimensionally. Also, the multiple photoelectric conversion elements 32 are arrayed three-dimensionally.

The scintillator 31 is not particularly limited, but may be any one of scintillator crystals selected from GAGG:Ce (Ce-doped Gd ₃ (Al,Ga) ₅ O ₁₂ ), LYSO:Ce (Ce-doped (Lu _1-x Y _x ) ₂ SiO ₅ ), and GSO (Gd ₂ SiO ₅ ).

Each of the photoelectric conversion elements 32 is attached to a plurality of scintillators 31. Specifically, each of the 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 element 32 and the scintillator 31 may be paired one-to-one, or one photoelectric conversion element 32 (i.e., one pixel photoelectric conversion element 32) may be provided across multiple scintillators 31 (i.e., multiple pixel scintillators 31). Each photoelectric conversion element 32 is configured to receive and detect (i.e., convert into an electrical signal) the light output from the scintillator 31 paired with the photoelectric conversion element 32, or from two or more scintillators 31 provided for the photoelectric conversion element 32. By monitoring the signal strength (signal strength of each pixel) from multiple photoelectric conversion elements 32 and performing center of gravity calculations, 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.

Furthermore, the photoelectric conversion element 32 can detect the intensity of the light output from the scintillator 31, thereby detecting the magnitude of the 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 the light output from the scintillator 31. The magnitude of the energy emitted from the gamma rays 20 to the scintillator 31 corresponds to a first emitted energy value in the scatterer 140, and corresponds to a second emitted energy value in the absorber 160.

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 released 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 released energy in the scatterer 140 and the timing at which the gamma ray 20 released energy in the absorber 160.

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

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

In the example of FIG. 4, the measuring 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 the emission of energy 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, and an amplifier circuit. When the scatterer 140 is realized by 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 the energy emission from the gamma rays 20 in the scatterer 140.

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, and an amplifier circuit. When the absorber 160 is realized by 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.

The hardware configuration of the first generating unit 170 is 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 further description is given of the case where the first generating unit 170 of the measuring device 10 is realized by a combination of hardware and software.

FIG. 5 is a diagram illustrating an example of a computer 1000 for realizing the first generation unit 170. The computer 1000 is any computer. For example, the computer 1000 is a SoC (System On Chip), a Personal Computer (PC), a server machine, a tablet terminal, or a smartphone. 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 one computer 1000, or may be realized by a combination of multiple computers 1000.

The computer 1000 has 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 connecting the processor 1040 and the like to each other is not limited to bus connection. The processor 1040 is one of various processors such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an FPGA (Field-Programmable Gate Array). The memory 1060 is a main storage device realized using a RAM (Random Access Memory) or the like. The storage device 1080 is an auxiliary storage device realized using a hard disk, an SSD (Solid State Drive), a memory card, or a ROM (Read Only Memory) or the like.

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 by a wireless connection or a wired connection.

The network interface 1120 is an interface for connecting the computer 1000 to a network. This communication network is, for example, a LAN (Local Area Network) or a WAN (Wide Area Network). The method for connecting the network interface 1120 to the network may be a wireless connection or a wired connection.

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

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

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 is explained below.

FIG. 6 is a diagram illustrating the relationship between the attenuator 120, the scatterer 140, and the absorber 160 and the path of the gamma ray 20 incident thereon. This diagram shows a phenomenon caused by a single photon of 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 is scattered at point P ₁ in the scatterer 140. The position of point P ₁ 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 point P ₂ in the absorber 160, where it is absorbed at point P _2. The position of point P ₂ corresponds to the absorption position described above. The x-axis, y-axis, and z-axis in FIG. 6 are three axes that are orthogonal to each other, with point P ₁ as the origin. The 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 side by side in the z direction. The direction from point _P2 to point _P1 is indicated by (θ, φ), and the scattering angle of Compton scattering is indicated by α.

What occurs in the scatterer 140 is Compton scattering of the gamma ray 20. When the positions of points _P1 and _P2 are specified, it is specified that the gamma ray 20 reached point _P1 via one of the generatrix of the Compton cone 42 as an arrival path. Then, candidates for the positions through which the gamma ray 20 passed in the object plane 40 (referred to as "candidate positions") are obtained as intersections between 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 in the object plane 40 describes a perfect circle or an ellipse.

On the other hand, it is not possible to determine which of the multiple candidate positions within the target plane 40 the gamma rays 20 have 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 rays 20 have passed through them.

Fig. 7 is a diagram illustrating the positional relationship between point _P1 and an ellipse 44. As described above, the ellipse 44 is a set of multiple candidate positions. Point P _C is one of the multiple candidate positions. In Fig. 7, the ellipse 44 and point P _C are projected onto the xy plane. Fig. 8 is a diagram illustrating the positional relationship between point _P1 and point P _C. Fig. 8 shows an example in which point _P1 is considered to be located within the top surface of the scatterer 140.

The gamma ray 20 passes through the attenuator 120 while reaching the point _P1 from the point _P2C . Here, as described above, the attenuator 120 transmits the incident gamma ray 20 with a probability according to 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 passing length L of the gamma ray 20 passing through the attenuator 122, and the lower the probability of the gamma ray 20 passing through the attenuator 120. In other words, the longer the length _L that the gamma ray 20 must pass through in the attenuator 122 while reaching the point _P1 , the more difficult it becomes for the gamma ray 20 to reach the point _P1 . In other words, the longer the length L that the gamma ray 20 must pass through in the attenuator 122 while reaching the point _P1 from the point _P2C , the lower the possibility that the gamma ray 20 actually passed through the point _P2C . Therefore, the first generating unit 170 can weight each of the multiple candidate positions based on the likelihood that the gamma ray 20 has passed through it, using the passing length L. It can be said that the passing length L is, for example, the length of the portion of the straight line connecting the point P _C and the point P ₁ that overlaps with the attenuation section 122.

The pass length L can be derived using the positional relationship between the point _P1 and the point _Pc . The pass length L can also be derived using the thickness _T1 of the attenuation section 122 in the z direction. Specifically, in the examples of Fig. 7 and Fig. 8, when the (x, y) coordinates of the point _Pc with the point _P1 as ^the origin are ( _xc , _yc ), the distance d between the projection point of the point _Pc onto the xy plane and the point _P1 is derived by d = √( _xc2 + _yc2 ⁾ . And the pass length L is derived by L = √( ^d2 + _T12 ) ^.

Note that while FIG. 8 shows an example in which the incident surface 120a of the attenuator 120 is the target plane 40, the target plane 40 is not limited to this example. The target plane 40 can be any surface 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.

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 if the incident surface 120a of the attenuator 120 is not the target plane 40, the first generator 170 may identify the incident position on the incident surface 120a of the attenuator 120 of the gamma ray 20 path corresponding to each candidate position, and then calculate the weight in the same manner.

As described above, FIG. 8 shows an example in which the point P ₁ is considered to be located within the uppermost surface of the scatterer 140, but the processing example is not limited to this example. For example, the point P ₁ may be considered to be located within the central surface in the thickness direction of the scatterer 140. In that case, (T ₁ +T ₂ /2) may be used instead of T ₁ in the derivation of the above-mentioned passing length L. Here, T ₂ is the thickness of the scatterer 140 in the z direction. Alternatively, the point P ₁ may be considered to be located within the lowermost surface of the scatterer 140. In that case, (T ₁ +T ₂ ) may be used instead of T ₁ in the derivation of the above-mentioned passing length L. If the three-dimensional coordinates of the point P ₁ in the scatterer 140 can be specified, the passing length L may be derived using the three-dimensional coordinates.

9 is a flow chart illustrating the flow of processing performed by the first generation unit 170. The first generation unit 170 identifies the 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 the passage length L for each of the multiple candidate positions (S20). In S20, the first generation unit 170 can derive the passage 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. Furthermore, the first generation unit 170 derives a weight w indicating the likelihood that the gamma ray 20 has passed through each of the multiple candidate positions using the passage length L (S30). Then, the first generation unit 170 generates first distribution information using the multiple candidate positions and the weights w for each of the multiple candidate positions (S40).

As described in detail below, the first generation unit 170 operates the measurement device 10 as a Compton camera. The first generation unit 170 generates first distribution information using the path length L that is assumed to be the path of the gamma rays 20 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.

The measurement method according to this embodiment and the processing performed by the first generation unit 170 are described in detail below. The first generation unit 170 can generate first distribution information based on the detection result of gamma rays 20 having an energy of, for example, 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 generation unit 170 can generate first distribution information regarding the incident direction of high-energy band gamma rays 20 into the attenuator 120. Gamma rays in such an energy band pass through a parallel collimator, making it difficult to measure them with a Single Photon Emission Computed Tomography (SPECT) device. Therefore, the use of the measurement device 10 according to this embodiment is beneficial.

Prior to measurement, the attenuator 120, the scatterer 140, and the absorber 160 are positioned so that the attenuator 120 faces the area to be measured. In other words, the attenuator 120 is located between the area to be measured and the scatterer 140. For example, the area to be measured is an area where a gamma ray source is estimated to be located. When the measurement device 10 is used for a nuclear medicine examination, the area to be measured is at least a part of the subject's body.

The user of the measuring device 10 also operates the first generating unit 170 to identify the target plane 40. The user of the measuring device 10 may input information for identifying the target plane 40 to the first generating 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 generating unit 170 may tentatively regard the incident surface 120a of the attenuating body 120 as the target plane 40 and perform the process described below. Thereafter, the first generating unit 170 can generate output data for any target plane 40. The user can operate the measuring device 10 using an input device such as a keyboard or mouse connected to the calculator 1000. The same applies below.

During measurement, multiple gamma rays 20 enter the attenuator 120 from the area to be measured. The gamma rays 20 that pass through the attenuator 120 are scattered by the scatterer 140. 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.

The scatterer 140 detects the emission of energy from the gamma ray 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.

For example, when the scatterer 140 is a detector 30 as described above, the first generating unit 170 detects a pulse in the signal output from the first control unit 142. The position information (coordinates) for each photoelectric conversion element 32 is determined in advance 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 timing of energy emission based on the timing of the detected pulse.

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.

For example, when the absorber 160 is a detector 30 as described above, the first generating unit 170 detects a pulse in the signal output from the second control unit 162. The position information (coordinates) for each photoelectric conversion element 32 is determined in advance 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 the absorption position information. The first generating unit 170 also identifies the second emission energy value based on the magnitude of the amplitude of the detected pulse. The first generating unit 170 then identifies the timing of energy emission based on the timing of the detected pulse.

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.

Then, 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 timing of energy emission in the scatterer 140 and the timing of energy emission in the absorber 160. Specifically, when the difference between the timing of energy emission in the scatterer 140 and the timing of energy emission 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).

The first generation 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).

The first generator 170 uses the scattering position information and the absorption position information to derive the 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.

The first generator 170 also calculates the value of cosα using the following formula (1): _{m e} c ² is the rest energy of the electron, E ₁ is the first emitted energy value, E ₂ is the second emitted energy value, and α is the scattering angle of Compton scattering.

Here, the equation of a conical surface (Compton cone) with the scattering position (point P ₁ ) as its apex is expressed by the following formula (2): Point P is a point on the conical surface. Vector v is a unit vector of the axis of the cone.

Furthermore, when the unit vector (θ, φ) is converted to Cartesian coordinates, the following equation (3) holds.

When the following equation (4), in which the point _P1 is the origin and the z coordinate of the target plane 40 is _zt , is substituted into equation (2) together with equation (3), the following equation (5) is obtained.

The first generator 170 identifies a point (x, y, _zt ) where the difference between the left and right sides of formula (5) is smaller than a predetermined threshold as a point on the curve where the cone intersects with the target plane 40, that is, as a candidate position. A plurality of such candidate positions are identified.

In this manner, the first generation unit 170 can identify the positions of multiple candidate positions. In other words, the first generation unit 170 can identify the distribution of the candidate positions.

Next, the first generating unit 170 derives the above-mentioned path length L for each of the multiple candidate positions (S20). The first generating unit 170 can geometrically derive the path length L using at least the scattering position information (point P ₁ ), the coordinates of the candidate position (point P _C ), and information indicating the area occupied by the attenuation section 122 in the attenuation body 120. The information indicating the area occupied by the attenuation section 122 in the attenuation body 120 is, for example, the thickness T ₁ of the attenuation section 122. The first generating unit 170 may further derive the path length L using the thickness T ₂ of the scatterer 140. An example of the derivation method is as described above with reference to FIG. 7 and FIG. 8.

Then, the first generating unit 170 uses the derived passage length L for each of the multiple candidate positions to derive a weight w (S30). The likelihood that the gamma ray 20 will pass through the passage thickness L is expressed as e ^-μL using the linear attenuation coefficient μ. The first generating unit 170 sets e ^-μL as the weight w, for example. The first generating unit 170 may further set a value obtained by multiplying e ^-μL by some coefficient or the like as the weight w. e is a natural number. μ is a coefficient that depends on the material constituting the attenuation unit 122 and the energy of the gamma ray 20. The first generating unit 170 may use a predetermined value of μ to calculate the weight w.

As another example, weight reference information (e.g., a table) may be prepared in advance that indicates the positional relationship between the scattering positions and the candidate positions, and the relationship with the weight w. In that 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.

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 the multiple position coordinates (i.e., the position coordinates of the multiple candidate positions).

The first generation unit 170 may further generate first distribution information for each of the multiple gamma rays 20 that pass through the attenuator 120. The multiple generated first distribution information may then be accumulated to generate cumulative distribution information. In this case, a weight w is added 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.

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 may output the output data in the form of a table or the like, or may output the output data as an image. In the image, the distribution may be shown with a color or brightness according to the weight w or the cumulative value of the weight w. The first generating unit 170 may also output the output data by superimposing it on an image of the measurement target area. The first generating unit 170 may display the output data on a display connected to the computer 1000 that realizes the first generating unit 170, or may output the output data to be stored in the storage device 1080 of the computer 1000 that realizes the first generating unit 170 or in a storage device external to the measuring device 10.

FIG. 10 is a diagram illustrating an example of an image showing the first distribution information generated by the first generation unit 170. An ellipse is displayed as a collection of multiple candidate positions, and the magnitude of the weight w, i.e., the likelihood, for each candidate position is indicated by color. In this way, the magnitude of the weight w, i.e., the likelihood, can be identified for multiple candidate positions.

11 is a diagram illustrating an example of cumulative distribution information according to a reference example. FIG. 12 is a diagram illustrating an example of cumulative distribution information according to this embodiment. The reference example in FIG. 11 shows an example in which no weighting is applied to the candidate positions, and all of the multiple candidate positions (i.e., ellipses) for each gamma ray 20 are uniformly shown. In this case, unless information on many gamma rays 20 is accumulated, it is not possible to determine where the gamma ray source is actually located (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 on a smaller number of gamma rays 20.

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

Second Embodiment
13 is a perspective view illustrating an attenuation body 120 according to the 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.

The attenuation body 120 according to this embodiment is a parallel collimator. In the example of FIG. 13, the attenuation body 120 has a plurality of walls of the attenuation section 122. The thickness of the wall of the attenuation section 122 is, for example, 0.1 mm or more and 3 mm or less. In the attenuation body 120, the walls of the attenuation section 122 are arranged in a lattice pattern. In other words, in the attenuation body 120, the attenuation section 122 is arranged, for example, to draw a plurality of rectangles. The inside of these rectangles may be empty. It can be said that the attenuation body 120 has 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.

For gamma rays 20 in the low energy band described below, only the gamma rays 20 that do not enter the attenuation section 122 and pass through the through hole pass through the attenuator 120. On the other hand, gamma rays 20 that enter the attenuation section 122 are absorbed by the attenuation 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 hole reaches the scatterer 140. On the other hand, for 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.

In the attenuator 120 according to this embodiment, the distance between the opposing walls of the attenuation section 122 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 120a is, for example, 3 mm or more and 15 mm or less. Note that the positional relationship between the walls of the attenuation section 122 in the attenuator 120 and the scintillator 31 and photoelectric conversion element 32 in the detector 30 is not particularly limited.

In this embodiment, the attenuator 120 is a parallel collimator, so that the measuring device 10 can also function as a SPECT device.

FIG. 14 is a diagram illustrating the functional configuration of the measuring device 10 according to this embodiment. The measuring device 10 according to this embodiment further includes a second generating unit 180. The second generating unit 180 generates arrival information regarding where the gamma rays 20 have come from, using absorption position information in the scatterer 140 of the gamma rays 20 absorbed by the scatterer 140. The second generating unit 180 causes the measuring device 10 to function as a SPECT device.

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

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, it can be said that the arrival information is information regarding gamma rays 20 with lower energy than the first distribution information.

In this embodiment, since the attenuator 120 is a parallel collimator, it is possible to block gamma rays 20 in the low energy band as described above that are incident on the attenuator 120 at an angle. Therefore, only gamma rays 20 that are incident on the incident surface 120a of the attenuator 120 from approximately the normal direction 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., they are not emitted from the scatterer 140.

The measurement flow when the measuring device 10 is made to function as a SPECT device is described in detail below. Prior to measurement, the attenuator 120, the scatterer 140, and the absorber 160 are positioned so that the attenuator 120 faces the region to be measured. In other words, the attenuator 120 is positioned between the region to be measured and the scatterer 140. For example, the region to be measured is an area where a gamma ray source is estimated to be located. When the measuring device 10 is used for nuclear medicine examination, the region to be measured is at least a part of the subject's body.

During measurement, multiple gamma rays 20 enter the attenuator 120 from the area to be measured. 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 enter the attenuator 120 necessarily pass through the attenuator 120. Gamma rays 20 that enter the attenuator 120 at an angle disappear inside the attenuator 120.

When the gamma ray 20 is absorbed by the scatterer 140, the release of energy from the gamma ray 20 to the scatterer 140 is detected. The second generation unit 180 acquires a signal indicating the detection result of the energy release 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 attenuator 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.

The second generation unit 180 further determines the magnitude of the energy (i.e., the 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 manner as the first generation unit 170 determines the first energy value. The second generation unit 180 associates this energy value with the absorption position information.

In addition, instead of the second generating unit 180 identifying 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 (identified) in another device. Then, the second generating unit 180 may acquire the information generated in the other device.

FIG. 15 is a flowchart illustrating the flow of processing performed by the second generation unit 180.

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.

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 about which information regarding where they came from is desired. If the energy absorbed by the scatterer 140 is within the target energy band, the second generation unit 180 treats 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 treat 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.

The second generation unit 180 may further generate arrival information for each of the multiple gamma rays 20 that pass through the attenuator 120. The multiple pieces of arrival information thus generated may then be accumulated to generate cumulative arrival information. Specifically, the second generation unit 180 adds up the number of gamma rays 20 detected (the 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.

The second generating unit 180 can output at least one of the arrival information and the accumulated 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 may output the data as an image. In the image, the distribution may be shown with a color or brightness according to the accumulated number of gamma rays 20. The second generating unit 180 may also output the output data by superimposing it 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 realizes the second generating unit 180, or may output the output data to be stored in the storage device 1080 of the computer 1000 that realizes the second generating unit 180 or in a storage device external to the measuring device 10.

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

The processing performed by the first generating unit 170 according to this embodiment is described below. The processing performed by the first generating unit 170 according to this embodiment is the same as the processing performed by the first generating unit 170 according to the first embodiment, except for the method of deriving the passing length L.

Fig. 16 is a diagram showing the relationship between the attenuation section 122 according to this embodiment, the scattering position (point _P1 ), and the candidate position (point _Pc ). In Fig. 16, the ellipse 44 and point _Pc are projected onto the xy plane. In Fig. 16, the wall of the attenuation section 122 is shown by vertical and horizontal straight lines. Also, a set of multiple candidate positions is shown by an ellipse, and point _Pc is one candidate position.

The first generating unit 170 according to this embodiment derives the passage 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., intervals) of the multiple walls of the attenuation unit 122 and the thickness of the walls. In this embodiment, the first generating 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 generating unit 170 can then derive the passage length L by multiplying the thickness of the wall 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 one wall in the vertical direction and two walls in the horizontal direction while traveling from point P _C to point P _1. Therefore, the number of walls through which the gamma ray 20 passes is three. The first generator 170 multiplies the wall thickness of the attenuation section 122 by 3 to obtain a value as the pass length L of the candidate position. The first generator 170 derives the weight w by using the pass length L in the same manner as in the first embodiment.

In this embodiment, as another example, weight reference information (e.g., a table) may be prepared in advance that indicates the positional relationship between the scattering positions and the candidate positions, and the relationship with the weight w. In that 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.

Next, the action and effect of this embodiment will be described. In this embodiment, the same action 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 the low energy band.

The present embodiment will be described in detail below with reference to examples. Note that the present embodiment is not limited in any way to the description of these examples.

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

Figure 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 about 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 Figure 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.

Further, a gamma ray source 92 was placed on the attenuator 120. ¹³³ Ba (356 keV) was used as the gamma ray source 92. The distance between the center of the attenuator 120 and the center of the gamma ray source 92 was 2 cm.

The cumulative distribution information shown in FIG. 18 was obtained by processing performed by the first generating 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 events (number of gamma rays) detected was 12,000. As shown in this figure, the position of the gamma ray source 92 was detected by the measuring device 10. Note that in FIG. 18, a plane including the bottom surface of the gamma ray source 92 is set as the target plane, and an XY plane with the center of the attenuator 120 as the origin is shown. The same applies to the subsequent FIGS. 19, 20, 22, 23, and 24.

(Comparative Example 1)
Measurements were performed in the same manner as in Example 1, except that no attenuator 120 was used and no weighting was applied to each of the multiple candidate positions. That is, the gamma ray source 92 was placed directly on the housing 91, and the multiple candidate positions obtained were treated uniformly. The distribution data of the multiple candidate positions of gamma rays thus obtained 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 events (number of gamma rays) detected was 24,000.

FIG. 20 is a profile 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 are integrated for each X coordinate, and the values are plotted in FIG. 20. From FIG. 20, it was confirmed that a sharper peak was obtained in Example 1 than in Comparative Example 1, and measurements were made with a high S/N ratio.

Example 2
Measurements were carried out in the same manner as in Example 1, except that two gamma ray sources 92 were placed on the attenuator 120 .

FIG. 21 is a diagram showing the measurement configuration for Example 2. The 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.

The cumulative distribution information shown in FIG. 22 was obtained by processing performed by the first generating 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 events (number of gamma rays) detected was 11,000. As shown in this figure, the positions of the two gamma ray sources 92 were detected by the measuring device 10.

(Comparative Example 2)
The measurements were performed in the same manner as in Example 2, except that no attenuator 120 was used and no weighting was applied to each of the multiple candidate positions. The gamma ray sources used and their arrangement were the same as in Example 2.

Similar to Comparative Example 1, the obtained multiple position candidates were treated uniformly to obtain the cumulative distribution information shown in Figure 23. The imaging time when the cumulative distribution information shown in Figure 23 was obtained was 10 minutes, and the number of events detected (number of gamma rays) was 20,000.

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

The above describes embodiments of the present invention with reference to the drawings, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted. For example, in the sequence diagrams and flow charts used in the above explanation, multiple steps (processing) are described in order, but the order in which the steps are executed in each embodiment is not limited to the order described. In each embodiment, the order of the steps shown in the figures can be changed to the extent that does not cause any problems in terms of content. Furthermore, the above-mentioned embodiments can be combined to the extent that the content is not contradictory.

10 Measuring device 20 Gamma ray 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 Attenuator 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 (8)

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 passed through the attenuator;
and an absorber that absorbs at least a portion of the gamma rays scattered by the scatterer. 2. The measuring device according to claim 1,
The measurement device further includes a first generation unit that generates first distribution information regarding the incident direction of the gamma ray into the attenuator using scattering position information of the gamma ray in the scatterer, absorption position information of the gamma ray in the absorber, a first emission energy value from the gamma ray to the scatterer, and a second emission energy value from the gamma ray to the absorber. 3. The measuring device according to claim 2,
The attenuator has an attenuation portion that attenuates the number of gamma rays,
A measurement device in which the first generation unit generates the first distribution information by further using a path length assumed to be taken by a gamma ray passing through the attenuation unit. 4. The measuring device according to claim 3,
The first generation unit is
Identifying a distribution of candidate positions through which the gamma ray may have passed within the target 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;
deriving the path length for each of a plurality of candidate positions based on a relationship between each of the candidate positions included in the distribution and a scattering position of the gamma ray in the scatterer;
deriving a weight indicating a likelihood that the gamma ray has passed through each of the plurality of candidate positions using the path length;
A measurement device that generates the first distribution information using the plurality of candidate positions and the weights for each of the plurality of candidate positions. The measuring device according to any one of claims 1 to 4,
The measuring device, wherein the attenuator is a parallel collimator. 6. The measuring device according to claim 5,
The measuring device further includes a second generating unit that generates arrival information regarding where the gamma rays came from, using absorption position information in the scatterer of the gamma rays absorbed in the scatterer. The measuring device according to any one of claims 1 to 6,
A measuring device, wherein the distance between the attenuator and the scatterer is 5 mm or less. Gamma rays are made to enter an attenuating body that transmits the incident gamma rays with a probability that depends on the angle of incidence,
At least a portion of the gamma rays that have passed through the attenuator is scattered by a scatterer;
A measuring method in which at least a portion of the gamma rays scattered by the scatterer is absorbed by an absorber.

Images