Radiation diagnostic device, Compton scattering event correction method and program

Abstract

To improve image quality.SOLUTION: A radiodiagnosis device according to an embodiment comprises: a first detector; a second detector; an identification unit; and a determination unit. The first detector is configured to detect Cherenkov light generating when radiation passes through. The second detector, which is provided oppositely on a distant side from a generation source of the radiation with respect to the first detector, is configured to detect energy information on the radiation. The identification unit is configured to identify a Compton scattering event to be detected by the second detector. The determination unit is configured to determine an event corresponding to an incidence channel of the identified Compton scattering event on the basis of a detection result of the first detector.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a radiation diagnostic apparatus, a method and a program for correcting Compton scatter events. [Background technology]

[0002] Positron Emission Tomography (PET) devices are known as radiation diagnostic devices. In PET devices, a pair of gamma rays is generated when a positron emitted by a radiopharmaceutical labeled with a positron-emitting nuclide annihilates with an electron, producing a pair of gamma rays. The pair of gamma rays is detected when the pair is incident on a scintillator, and the position of the positron annihilation is identified by detecting the scintillation light, and medical images are generated using the detected light.

[0003] However, since scintillation light is light re-emitted in the transition process in which the excited state generated by the annihilation gamma rays returns to the ground state over time, the response speed is relatively slow and errors may occur in identifying the annihilation position of the positron. For this reason, it is conceivable to identify the annihilation position of the positron by using, for example, a detector that detects the scintillation light and a detector that detects the Cherenkov light in combination.

[0004] As a result, by using a Cherenkov photodetector with excellent time resolution and a scintillation photodetector with excellent energy resolution in combination, it is possible to improve the image quality of a radiation diagnostic apparatus.

[0005] Here, even when a detector that detects scintillation light and a detector that detects Cherenkov light are used in combination, there are events that undergo Compton scattering and then cause a photoelectric effect in the detector that detects scintillation light, just as in the case where only a detector that detects scintillation light is used. If it is possible to image such events that undergo Compton scattering and then cause a photoelectric effect, further improvement in image quality can be expected. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-191086 A [Patent Document 2] JP 2002-116256 A Summary of the Invention [Problem to be solved by the invention]

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve image quality. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0008] A radiological diagnostic apparatus according to an embodiment includes a first detector, a second detector, an identification unit, and a decision unit. The first detector detects Cherenkov light generated when radiation passes through. The second detector is provided facing the first detector on a side farther from a source of the radiation, and detects energy information of the radiation. The identification unit identifies Compton scattering events detected by the second detector. The decision unit determines an event corresponding to an incident channel from among the identified Compton scattering events based on a detection result by the first detector. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of a radiation diagnostic apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating the counting process in the radiation diagnostic apparatus according to the first embodiment. [Diagram 3] FIG. 3 is a diagram illustrating the background according to the embodiment. [Figure 4]FIG. 4 is a diagram illustrating the background according to the embodiment. [Diagram 5] FIG. 5 is a diagram illustrating the processing performed by the radiation diagnostic apparatus according to the first embodiment. [Figure 6] FIG. 6 is a flowchart illustrating the flow of processing in the radiation diagnostic apparatus according to the first embodiment. [Figure 7] FIG. 7 is a flowchart illustrating in more detail the process flow of step S130 in FIG. [Figure 8] FIG. 8 is a diagram illustrating the process flow of step S130 in the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating the process according to the second embodiment. [Figure 10] FIG. 10 is a diagram illustrating the process according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a radiation diagnostic apparatus, a method for correcting a Compton scattering event, and a program according to an embodiment will be described in detail with reference to the drawings.

[0011] (First embodiment) First, the configuration of a radiation diagnostic apparatus according to an embodiment will be described with reference to FIG. 1, taking a PET apparatus as an example.

[0012] 1 is a diagram showing the configuration of a PET apparatus 100, which is a radiation diagnostic apparatus according to an embodiment. As shown in FIG. 1, the PET apparatus 100 according to the embodiment includes a gantry device 10 and a console device 20.

[0013] The gantry device 10 detects a pair of annihilation gamma rays emitted from a positron in the subject P by a first detector 1 for detecting Cherenkov light and a second detector 2 for detecting scintillation light, which are arranged in a ring shape surrounding the subject P. The gantry device 10 also generates counting information from the output signals of the first detector 1 and the second detector 2 by a first timing information acquisition circuit 101 and a second timing information acquisition circuit 102.

[0014] More specifically, the gantry device 10 includes a tabletop 103, a bed 104, a bed drive unit 105, a first detector 1 that detects Cherenkov light, a second detector 2 that detects scintillation light, a first timing information acquisition circuit 101 that generates counting information from the first detector 1, and a second timing information acquisition circuit 102 that generates counting information from the second detector 2.

[0015] The first detector 1 is a detector that obtains counting information related to the annihilation gamma rays emitted from the positrons in the subject P by detecting Cherenkov light, which is a shock wave light generated when a charged particle generated by the interaction of the pair annihilation gamma rays emitted from the positrons in the subject P with an internal light-emitting body (radiator) moves at a speed faster than the phase speed of light in the medium. That is, the first detector 1 detects Cherenkov light generated when radiation passes through.

[0016] The first detector 1, which is a detector for pair annihilation gamma rays using Cherenkov light, is disadvantageous in terms of sensitivity to energy compared to a detector for pair annihilation gamma rays using scintillation light. However, Cherenkov light is generated in a very short time compared to scintillation light, so that the response characteristic is good, and the first detector 1, which is a detector using a method for detecting Cherenkov light, has a characteristic that it is advantageous in terms of time resolution compared to a detector using a method for detecting scintillation light.

[0017] In other words, the first detector 1, which is a detector that detects Cherenkov light, has a characteristic that is advantageous in terms of time resolution compared to the second detector 2, which is a detector that detects scintillation light, while the second detector 2, which is a detector that detects scintillation light, has a characteristic that is advantageous in terms of energy resolution compared to the first detector 1, which is a detector that detects Cherenkov light.

[0018] Therefore, the radiation diagnostic apparatus according to the embodiment generates counting information using the first detector 1 and the second detector 2. This makes it possible to generate counting information that maintains both energy resolution and high time resolution.

[0019] Returning to the explanation of the configuration of the first detector 1, the first detector 1 has, for example, a light-emitting body (radiator) made of a medium that generates Cherenkov light by interacting with annihilation gamma rays, which are radiation emitted from positrons in the subject P, and a photodetector element that detects the generated Cherenkov light.

[0020] Here, the light emitter in the first detector 1 may be, for example, a medium that contains atoms with a large atomic number that have the property of easily causing a photoelectric effect due to the interaction of incident radiation, while not easily generating scintillation light that becomes noise, such as bismuth germanate (BGO, Bismuth Germanium Oxide), lead glass (SiO2+PbO), lead fluoride (PbF2), PWO (PbWO4), and other lead compounds. In other words, the light emitter in the first detector 1 is composed of, for example, a medium that is easily prone to a photoelectric effect, but suppresses scintillation due to radiation.

[0021] The photodetector detects the generated Cherenkov light. The photodetector 51 is, for example, a silicon photomultiplier (SiPM), which is an APD (Avalanche Photo Diode) array with individual pixels each having a size of several tens of microns, and operates in Geiger mode. As another example, the photodetector 51 is made up of a plurality of pixels that perform photoelectric conversion, and each of these pixels is made up of, for example, a single photon avalanche diode (SPAD).

[0022] The second detector 2 is a detector that detects radiation by detecting scintillation light (fluorescence), which is light that is re-emitted when a substance that has become excited as a result of annihilation gamma rays emitted from positrons in the subject P interacting with a light emitter (scintillator) transitions back to the ground state. The second detector 2 is a detector that simultaneously detects radiation energy information of the annihilation gamma rays emitted from positrons in the subject P.

[0023] In order to prevent the gamma rays from losing all their energy in these light emitters, the thickness of the light emitters 50 in the first detector 1 may be designed to be smaller than the thickness of the scintillator 60 provided in the second detector 2. This allows the pair-produced gamma rays to generate Cherenkov light in the first detector 1 while retaining most of their energy and to enter the second detector 2, where they can generate scintillation light.

[0024] Furthermore, the pixel size of the light emitter 50 in the first detector 1 can be made smaller than, for example, the pixel size of the scintillator 60 in the second detector 2. This can relatively increase the position resolution of data obtained from the first detector 1. Furthermore, the detector row length of the first detector may be configured to be shorter than the detector row length of the second detector.

[0025] The second detector 2 is provided facing the first detector 1 that detects Cherenkov light on the side farther from the source of radiation, i.e., annihilation gamma rays emitted from positrons in the subject P. As an example, the second detector 2 is arranged in a ring-like manner by dividing the first detector 1 into a plurality of detector blocks that further surround the periphery of the subject P in a ring-like manner. As an example, the second detector 2 is a ring-shaped detector like the first detector 1, and the diameter of the second detector 2 is larger than the diameter of the first detector 1.

[0026] As described above, the generation of scintillation light is a slower process than the generation of Cherenkov light. On the other hand, most of the energy of the annihilation gamma rays is converted into scintillation light, so from the viewpoint of measuring the energy of the annihilation gamma rays, the second detector 2 using scintillation light is more advantageous than the first detector 1 using Cherenkov light.

[0027] The second detector 2 is composed of multiple pixels. One pixel of the detector here refers to the smallest separation unit of the detector's position resolution. For example, if each of multiple photodetection elements detects scintillation light generated at a different position, each of the multiple photodetection elements becomes a detector of one pixel. Conversely, if each of multiple photodetection elements detects scintillation light generated at the same position, the multiple photodetection elements collectively become a detector of one pixel.

[0028] In the embodiment, similarly to the first detector 1, one photodetection element constituting the second detector 2 may be configured as a multi-pixel photodetection element.

[0029] In addition, while Fig. 1 shows an example in which the detector 2 is composed of a plurality of detector blocks, one pixel in Fig. 2 means a pixel unit capable of separating the generation position of Cherenkov light, and may be a unit finer than the detector block unit shown in Fig. 1. In other words, each detector block of the second detector 2 configured in a ring shape shown in Fig. 1 may be composed of a plurality of pixels.

[0030] Next, an example of a specific configuration of the second detector 2 is a photon-counting, Anger-type detector, and includes, for example, a scintillator, a photodetector element, and a light guide (not shown).

[0031] The scintillator converts the annihilation gamma rays emitted from the positrons in the subject P and incident thereon into scintillation light (scintillation photons, optical photons), and outputs the light. The scintillator is formed of scintillator crystals suitable for TOF measurement and energy measurement, such as LaBr3 (Lanthanum Bromide), LYSO (Lutetium Yttrium Oxyorthosilicate), LSO (Lutetium Oxyorthosilicate), LGSO (Lutetium Gadolinium Oxyorthosilicate), or BGO, and is arranged, for example, two-dimensionally.

[0032] The photodetector element may be, for example, the aforementioned SiPM (Silicon photomultiplier) or a photomultiplier tube. A photomultiplier tube has a photocathode that receives scintillation light and generates photoelectrons, multiple dynodes that provide an electric field to accelerate the generated photoelectrons, and an anode that is an electron outlet, and amplifies the scintillation light output from the scintillator and converts it into an electrical signal.

[0033] The light guide is made of a material such as a plastic material with excellent optical transparency, and transmits the scintillation light output from the scintillator to a photodetector element such as a SiPM or a photomultiplier tube.

[0034] Next, other configurations will be described.

[0035] The first timing information acquisition circuit 101 generates counting information from the output signal of the first detector 1, and stores the generated counting information in the memory 142 of the console device 20. Although not shown in Fig. 1, the first detector 1 is divided into a plurality of blocks, and each block is provided with a first timing information acquisition circuit 101.

[0036] The first timing information acquisition circuit 101 converts the output signal of the first detector 1 into digital data and generates counting information. This counting information includes the detection position and detection time of the annihilation gamma ray. For example, the first timing information acquisition circuit 101 identifies a plurality of photodetection elements that converted the Cherenkov light into an electrical signal at the same timing. Then, the first timing information acquisition circuit 101 calculates the position of the center of gravity using the position of each identified photodetection element and the intensity of the electrical signal, and identifies the detection element number (P) that indicates the position of the radiator into which the annihilation gamma ray is incident.

[0037] The first timing information acquisition circuit 101 also identifies the detection time (T) at which the Cherenkov light generated by the annihilation gamma ray is detected by the first detector 1. The detection time (T) may be an absolute time or may be the elapsed time from the start of imaging. In this way, the first timing information acquisition circuit 101 generates counting information including the detection element number (P) and the detection time (T).

[0038] The second timing information acquisition circuit 102 generates counting information from the output signal of the second detector 2, and stores the generated counting information in a memory 142 of the console device 20. As in the case of the first detector 1, the second detector 2 is divided into a plurality of blocks, and each block is provided with a second timing information acquisition circuit 102.

[0039] The second timing information acquisition circuit 102 converts the output signal of the second detector 2 into digital data to generate counting information. This counting information includes the detection position, energy value, and detection time of the annihilation gamma ray. For example, the second timing information acquisition circuit 102 identifies a plurality of photodetection elements that have converted the scintillation light into an electric signal at the same timing. Then, the second timing information acquisition circuit 102 identifies a scintillator number (P) indicating the position of the scintillator into which the annihilation gamma ray is incident. The means for identifying the scintillator position into which the annihilation gamma ray is incident may be by performing a center of gravity calculation based on the position of each photodetection element and the intensity of the electric signal. In addition, when the element sizes of the scintillator and the photodetection element correspond to each other, the scintillator corresponding to the photodetection element from which the output is obtained may be identified as the scintillator position into which the annihilation gamma ray is incident.

[0040] Moreover, the second timing information acquisition circuit 102 identifies the energy value (E) of the annihilation gamma ray incident on the second detector 2 by integrating the intensity of the electrical signal output from each photodetector element. The second timing information acquisition circuit 102 also identifies the detection time (T) at which the second detector 2 detects the scintillation light due to the annihilation gamma ray. The detection time (T) may be an absolute time or may be the elapsed time from the start of imaging. In this way, the second timing information acquisition circuit 102 generates counting information including the scintillator number (P), the energy value (E), and the detection time (T).

[0041] The first timing information acquisition circuit 101 and the second timing information acquisition circuit 102 is realized by a circuit such as a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), an Application Specific Integrated Circuit (ASIC), or a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)).

[0042] The top board 103 is a bed on which the subject P is placed, and is placed on the bed 104. The bed driving unit 105 moves the top board 103 under the control of a bed control function 105e of the processing circuit 105. For example, the bed driving unit 105 moves the subject P into the imaging opening of the gantry device 10 by moving the top board 103.

[0043] The console device 20 accepts operations of the PET device 100 by an operator, controls the capturing of PET images, and reconstructs the PET images using the counting information collected by the gantry device 10. As shown in Fig. 1, the console device 20 includes a processing circuit 105, an input device 140, a display 141, and a memory 142. The various components of the console device 20 are connected via a bus.

[0044] In the embodiment, each processing function performed by the identifying function (coincidence counting information generating function) 105a, the determining function 105b, the image generating function 105c, the system controlling function 105d, the bed controlling function 105e, the acquiring function 105f, and the calculating function 105g is stored in the memory 142 in the form of a program executable by a computer. The processing circuitry 105 is a processor that realizes a function corresponding to each program by reading the program from the memory 142 and executing it. In other words, the processing circuitry 105 in a state in which each program has been read has each function shown in the processing circuitry 105 in FIG. 1. 1, the processing functions performed by the specific function (coincidence counting information generating function) 105a, the determining function 105b, the image generating function 105c, the system control function 105d, the bed control function 105e, the acquiring function 105f, and the calculating function 105g are described as being realized by a single processing circuit 105, but the processing circuit 105 may be configured by combining a plurality of independent processors, and each processor may execute a program to realize the function. In other words, each of the above-mentioned functions may be configured as a program, and one processing circuit 105 may execute each program. As another example, a specific function may be implemented in a dedicated independent program execution circuit.

[0045] In addition, in Figure 1, the identification function 105a, the determination function 105b, the image generation function 105c, the system control function 105d, the bed control function 105e, the acquisition function 105f, and the calculation function 105g are examples of the identification unit, the determination unit, the image generation unit, the system control unit, the bed control unit, the acquisition unit, and the calculation unit, respectively.

[0046] The term "processor" used in the above description means a circuit such as a CPU (Central Processing Unit), a GPU (Graphical Processing Unit), an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)). The processor realizes functions by reading and executing a program stored in memory 142.

[0047] The processing circuit 105, using a specific function (coincidence counting information generating function) 105a, generates coincidence counting information based on the counting information regarding the first detector 1 acquired by the first timing information acquisition circuit 101 and the counting information regarding the second detector 2 acquired by the second timing information acquisition circuit 102, and stores the generated coincidence counting information in memory 142.

[0048] As described later, the processing circuit 105 performs processing related to Compton scattering correction using the identification function 105a and the determination function 105b. For example, the processing circuit 105 identifies a Compton scattering event detected by the second detector using the identification function 105a. The processing circuit 105 determines an event corresponding to an incident channel among the identified Compton scattering events based on the detection result by the first detector using the determination function 105b. Detailed processing of the identification function 105a, the determination function 105b, the acquisition function 105f, and the calculation function 105g will be described later.

[0049] The processing circuitry 105 reconstructs a PET image by the image generation function 105c. Specifically, the processing circuitry 105 reads out a time series list of coincidence counting information stored in the memory 142 by the image generation function 105c, and reconstructs the PET image by using the read out time series list. The processing circuitry 105 also stores the reconstructed PET image in the memory 142.

[0050] The processing circuitry 105 controls the gantry device 10 and the console device 20 by using a system control function 105d, thereby performing overall control of the PET device 100. For example, the processing circuitry 105 controls imaging in the PET device 100 by using the system control function 105d.

[0051] The processing circuit 105 controls the bed driving unit 105 by the bed control function 105e.

[0052] The input device 140 is a mouse, a keyboard, or the like used by an operator of the PET device 100 to input various instructions and settings, and transfers the input instructions and settings to the processing circuitry 105. For example, the input device 140 is used to input an instruction to start imaging.

[0053] The display 141 is a monitor or the like referred to by the operator, and under the control of the processing circuitry 105, displays the subject's respiratory waveform and PET images, and also displays a GUI (Graphical User Interface) for receiving various instructions and settings from the operator.

[0054] The memory 142 stores various data used in the PET device 100. The memory 142 is realized by, for example, a semiconductor memory element such as a random access memory (RAM) or a flash memory, a hard disk, an optical disk, etc. The memory 142 stores counting information in which a scintillator number (P), an energy value (E), and a detection time (T) are associated with each other, coincidence information in which a set of counting information is associated with a coincidence number that is a serial number of the coincidence information, a reconstructed PET image, etc.

[0055] Next, the generation of coincidence counting information in the case where the Compton scattering event in the second detector is not taken into consideration will be described with reference to FIG.

[0056] 2, consider a case where Cherenkov light originating from a pair of gamma rays pair-generated at the annihilation point Q is detected by detectors 1x and 1y, which are the first detector 1 that detects Cherenkov light, and scintillation light of a pair of gamma rays pair-generated at the annihilation point Q is detected by detectors 2x and 2y, which are the second detector 2 that detects scintillation light. In this case, the processing circuit 105 generates coincidence counting information by using data obtained from the pair of detectors, the first detector 1 and the pair of detectors, the second detector 2, and two pairs of detectors, by the specific function 105a.

[0057] As will be described later, when the pair of gamma rays generates Cherenkov light, the momentum of the gamma rays changes due to the presence of recoil electrons, so the trajectory of the gamma rays actually deviates from the original trajectory of the gamma rays by a small angle.

[0058] Next, the background of the embodiment will be described.

[0059] One way to improve the time resolution of PET devices is to use Cherenkov light, which is generated when charged particles travel through a material, for time-resolved measurements. One example is a dual-ring detector. In dual-ring and other detectors, the timing of an event is detected by detecting Cherenkov light with the inner ring, and the energy information of the event is detected by detecting scintillation light with the outer ring. This allows the Cherenkov light to be used for time-resolved measurements, improving the time resolution of the PET device.

[0060] Here, it is known that pair annihilation gamma rays are scattered in the scintillator due to the Compton effect. When Compton scattering occurs in a scintillator, it may cause an interaction with an adjacent scintillator other than the incident scintillator. For example, as shown in FIG. 3, one of the gamma rays generated as a pair from the annihilation point Q causes Compton scattering in detector 2a, which is one of the second detectors 2, and as a result, signals are observed in detectors 2a and 2b.

[0061] A schematic diagram of such a situation is shown in Fig. 4. As shown in Fig. 4, the incident gamma ray 11 entering the second detector 2a interacts with electrons due to Compton scattering, imparting energy to the electrons. As a result, the energy of the electrons changes, and recoil electrons 12 are generated. Furthermore, as a result of the incident gamma ray 11 transferring its energy to the recoil electrons 12, the energy of the incident gamma ray 11 changes, and it becomes a gamma ray 13 after Compton scattering.

[0062] Here, the recoil electrons 12 transfer their energy to the detector 2a through various processes, and the incident gamma rays 11 transfer their energy to the detector 2b through the photoelectric effect, so that as a result, signals are observed in both the detectors 2a and 2b. Here, if it is known whether the gamma rays first entered the detector 2a or the detector 2b where the signal is observed, it becomes possible to estimate the correct LOR.

[0063] Here, the energy of the incident gamma ray 11 is Eγ The energy imparted by the incident gamma ray 11 to the recoil electron 12 due to Compton scattering is E θ , the energy of gamma ray 13 after Compton scattering is E γ' Then, the following equation (1) holds.

[0064]

number

[0065] In addition, when the incident gamma ray 11 is Compton-scattered by a stationary electron, the energy of the recoil electron 12 after Compton scattering is the energy E e is equal to

[0066] In addition, the energy E given to the recoil electron 12 by the incident gamma ray 11 due to Compton scattering is e It is known that, although it depends on the scattering direction of the recoil electron, it has a maximum value. The energy E given to the recoil electron 12 by the incident gamma ray 11 due to Compton scattering e reaches a maximum value when the recoil electron is scattered in the opposite direction to the incident gamma ray 11, i.e., backscattering, and the spectrum corresponding to the energy at this time is called the Compton edge. In other words, the energy E e is an energy greater than or equal to 0 and less than the energy corresponding to the Compton edge. Also, the energy E of gamma ray 13 after Compton scattering γ' is an energy equal to or greater than the energy of the incident gamma ray 11 minus the energy corresponding to the Compton edge, and is an energy equal to or less than the energy of the incident gamma ray 11.

[0067] In addition, the energy E of gamma ray 13 after Compton scattering γ' The specific expression for is given by the following equation (2), where m0 is the mass of the electron, c is the speed of light, and θ is the scattering angle.

[0068]

number

[0069] In an actual situation, since the incident direction and scattering angle 14 of the incident gamma ray 11 are unknown, it is not possible to know which of the signals from detector 2a and detector 2b corresponds to the initial gamma ray incident position. As a result, an error may occur in estimating the LOR (Line Of Response).

[0070] In view of this background, the radiation diagnostic apparatus according to the first embodiment uses information from a first detector that detects Cherenkov light to identify an event corresponding to an incident channel among Compton scattering events. This makes it possible to estimate the incident position of a gamma ray during Compton scattering, and to estimate the LOR more accurately. This makes it possible to improve the spatial resolution of a PET image.

[0071] 4, for the sake of simplicity, the description of the deviation of the trajectory of the gamma rays due to the interaction of the pair annihilation gamma rays with the first detector 1 is omitted, but in reality, due to the generation of recoil electrons when the pair annihilation gamma rays generate Cherenkov light in the first detector 1, the trajectory of the pair annihilation gamma rays after passing through the first detector 1 deviates by a small angle from the trajectory of the pair annihilation gamma rays before passing through the first detector 1. In the embodiment, the Compton correction is performed taking such an effect into consideration.

[0072] This will be explained with reference to FIG.

[0073] First, when a 511 keV pair-annihilation gamma ray 15 enters the first detector 1, the pair-annihilation gamma ray 15 interacts with the first detector 1, causing Compton scattering, which generates a recoil electron 16. Here, Cherenkov light is generated by the recoil electron 16 moving through the material. Meanwhile, since the pair-annihilation gamma ray 15 transfers part of its energy to the recoil electron 16, the energy of the gamma ray 17 changes from that of the pair-annihilation gamma ray 15. In other words, the trajectory of the gamma ray 17 deviates from the trajectory of the pair-annihilation gamma ray 15 by a scattering angle 18.

[0074] Incidentally, since the value of scattering angle 18 is usually a relatively small angle, in the case of simple handling, the value of scattering angle 18 may be treated as 0.

[0075] Subsequently, the gamma ray 17 that becomes the incident gamma ray to the second detector 2a undergoes Compton scattering in the second detector 2a, and as a result, signals are detected in multiple detectors of the second detector 2. For example, the gamma ray 17 that becomes the incident gamma ray to the second detector 2 undergoes Compton scattering in the second detector 2a, and as a result, recoil electrons 19 and gamma rays 20 are generated. Here, the trajectory of the gamma ray 20 is shifted by a scattering angle 21 from the gamma ray 17 that becomes the incident gamma ray to the second detector 2a. The recoil electrons 19 are detected by the second detector 2a, and the gamma ray 20 is detected by the second detector 2b, and as a result, signals are detected by both the second detector 2a and the second detector 2b.

[0076] Next, the flow of the process of Compton correction performed by the radiation diagnostic apparatus according to the embodiment will be described with reference to Fig. 6 and Fig. 7. First, the overall flow including the process related to the event in which Compton correction is not performed will be described with reference to Fig. 6. Note that the embodiment can be applied to both the case in which one gamma ray of pair annihilation gamma rays is Compton scattered and the case in which both gamma rays of pair annihilation gamma rays are Compton scattered.

[0077] First, in step S100, the processing circuit 105 acquires timing information and energy information of pair annihilation gamma rays from the second detector 2 by the acquisition function 105f. Here, the timing information of pair annihilation gamma rays in the second detector 2 is, for example, counting information including the scintillator number (P) and detection time (T). In addition to this, the processing circuit 105 acquires counting information including the energy value (E) of the pair annihilation gamma rays incident on the scintillator by the acquisition function 105f.

[0078] Next, in step S105, the processing circuit 105 uses the identification function 105a to identify, for the event detected by the second detector, a Compton scattering event in the second detector 2, i.e., an event that has gone through Compton scattering and then caused a photoelectric effect in the second detector 2, based on the energy window for Compton scattering correction. That is, the processing circuit 105 uses the identification function 105a to identify a Compton scattering event based on energy information, time information and detection channel information of the event detected by the second detector.

[0079] Here, we will first explain the case where we ignore the change in gamma ray energy in the first detector 1 and consider that the energy of gamma ray 17 that becomes the incident gamma ray on the second detector 2 is equal to 511 keV, which is the energy of annihilation gamma ray 15.

[0080] In this case, when the energy detected by the second detector 2 is within a predetermined range from the energy of the annihilation gamma ray 15, i.e., within a predetermined range from 511 keV, the processing circuit 105 determines by the specific function 105a that the event for which timing information and energy information were obtained in step S100 is a normal signal event not involving Compton scattering, and performs the processing of step S140 described below.

[0081] On the other hand, when the signal is observed in a plurality of channels in the second detector 2 by the specific function 105a, and the total value of the energy detected in the second detector 2 is within a predetermined range from the energy of the pair annihilation gamma ray 15, that is, within a predetermined range from 511 keV, the processing circuit 105 determines that the event for which the timing information and the energy information are acquired in step S100 is a signal event related to the photoelectric effect after Compton scattering, and performs the processing of steps S120 to S130. Also, when the total value of the energy detected in the second detector 2 by the specific function 105a is not within a predetermined range from the energy of the pair annihilation gamma ray 15, that is, not within a predetermined range from 511 keV, the processing circuit 105 does not use the data of the event for generating a medical image.

[0082] In addition, the processing circuit 105 may use the identification function 105a to identify a Compton scattering event in the second detector 2 by taking into account the change in energy of the gamma ray in the first detector 1, i.e., the energy change from annihilation gamma ray 15 to gamma ray 17.

[0083] Proceeding to step S110, for an event detected by the second detector that the processing circuit 105 determines to be a Compton scattering event by the identification function 105a (step S110 Yes), the processing circuit 105 performs processing of steps S120 and S130 by the decision function 105b, and estimates the gamma ray incidence position in the second detector.

[0084] Specifically, first, in step S120, the processing circuit 105 uses the decision function 105b to identify and extract event information in the first detector 1 based on the Compton scattering event identified in step S105 and geometry information of the PET device 100.

[0085] That is, if the time when the Cherenkov light is detected in the first detector 1 is t1, the time when the scintillation light is detected in the second detector 2 is t2, and the distance between the location where the Cherenkov light is detected in the first detector 1 and the location where the scintillation light is detected in the second detector 2 is L, then since the gamma rays 17 move in space at the speed of light c, if the signal detected in the first detector 1 and the signal detected in the second detector 2 relate to the same event, it is considered that the relationship L=ct holds. For example, by determining whether such a relationship holds between the signal detected in the first detector 1 and the signal detected in the second detector 2, the processing circuit 105 extracts event information in the first detector 1 corresponding to the Compton scattering event identified in step S105 by the identification function 105a, based on the Compton scattering event identified in step S105, taking into account the geometry information of the PET device 100. Here, the event information in the first detector 1 is, for example, a list of detection element numbers (P) and detection times (T). In this manner, the processing circuit 105 uses the determination function 105b to extract a Cherenkov event corresponding to the Compton scattering event identified in step S105 based on the time information of the event detected by the first detector and the detection channel position information of the first detector.

[0086] Next, in step S130, the processing circuit 105 uses the determination function 105b to estimate the gamma ray incident position in the second detector 2 based on the event information in the first detector 1 identified in step S120. That is, the processing circuit 105 uses the determination function 105b to determine the gamma ray incident channel based on the Cherenkov event identified in step S120. The processing of this step will be described later.

[0087] Next, in step S150, the processing circuit 105 uses a determination function to estimate a line of response (LOR) based on the gamma ray incidence position estimated in step S130. The processing of this step will also be described later.

[0088] Next, in step S160, the processing circuitry 105 performs processing similar to the image generation procedure of a normal PET device using the image generation function 105c, and generates a medical image based on the LOR estimated in step S150.

[0089] Returning to step S110, for events detected by the second detector other than those determined by the processing circuit 105 using the identification function 105a to be normal events not involving Compton scattering (step S110 No), the processing circuit 105 performs normal processing using the decision function 105b to identify event information in the first detector corresponding to the event detected by the second detector (step S140). Specifically, similar to step S120, the processing circuit 105 uses the identification function 105a to identify event information in the first detector 1 corresponding to the event identified in step S100 based on the event identified in step S100, taking into account geometry information of the PET device 100.

[0090] Next, in step S150, the processing circuit 105 uses the determination function 105b to estimate the LOR based on the event information identified in step S140. For example, the processing circuit 105 uses the determination function 105b to estimate, as the LOR, a straight line connecting two detection elements in which the Cherenkov light is detected in the first detector.

[0091] Next, the processes of steps S130 and S150 will be described in more detail with reference to Fig. 7. Fig. 7 is a flowchart illustrating the process procedure of step S130 in Fig. 6 in more detail.

[0092] First, in step S131, the processing circuit 105 uses the determination function 105b to estimate the number of photons N generated by Cherenkov light based on the signal intensity obtained by the first detector 1. That is, the processing circuit 105 uses the determination function 105b to estimate the number of Cherenkov photons related to the Cherenkov event based on the data obtained by the first detector 1.

[0093] Next, in step S132, the processing circuit 105 determines, by the determination function 105b, the energy E e Estimate.

[0094] More specifically, if the number of photons generated by Cherenkov light is N, x is a variable representing the radial thickness of the Cherenkov light detector, λ is the wavelength of the Cherenkov light, α is a constant, n(λ) is the refractive index, v is the speed of the recoil electron, c is the speed of light, and nβ=v / c, the following equation (3) holds.

[0095]

number

[0096] Moreover, by integrating equation (3) with respect to x, the following equation (4) holds, where L is the thickness of the Cherenkov photodetector.

[0097]

number

[0098] Here, if the wavelength range of Cherenkov light detectable by the first detector 1 is from λ1 to λ2, then by integrating equation (4) over this range, the number N of photons of Cherenkov light generated by the first detector 1 is expressed by the following equation (5).

[0099]

number

[0100] Here, in equation (5), the number of photons N generated by the Cherenkov light is related to the velocity v of the recoil electron 16 through β in equation (5). Therefore, by solving equation (5) for β, the processing circuit 105 can estimate the velocity v of the recoil electron 16 based on the number of photons N generated by the Cherenkov light using the decision function 105b. Therefore, the processing circuit 105 can determine the energy E of the recoil electron 16 based on the estimated velocity v of the recoil electron 16 using the decision function 105b. e can be estimated.

[0101] Next, in step S133, the processing circuit 105 determines, by the determination function 105b, the energy E of the recoil electron 16 estimated in step S132. e Based on this, the processing circuit 105 calculates the scattering angle 18 in the first detection channel (first detector 1) by the determination function 105b. Specifically, first, the processing circuit 105 uses the law of conservation of energy and the law of conservation of momentum to determine the energy E γ、 Momentum p of annihilation gamma ray 15 γ、 Energy E of recoil electron 16 e、 and the momentum p of the recoil electron 16 e Based on the energy and momentum of the gamma rays 17, the processing circuit 105 calculates the energy and momentum of the gamma rays 17. Next, the processing circuit 105 calculates the scattering angle 18 based on the calculated energy and momentum of the gamma rays 17 by the determination function 105b.

[0102] Next, in step S134, the processing circuit 105 determines, by the determination function 105b, the incident channel of the gamma ray 17 in the second detector 2 based on the detection channel of the first detector 1 in which the Cherenkov event was detected and the scattering angle 18 at the detection channel of the first detector 1. Specifically, the processing circuit 105 determines, by the determination function 105b, the incident channel based on the point where the Compton cone corresponding to the scattering angle 18, which spreads from the detection channel of the first detector 1, intersects with the second detector 2.

[0103] Next, the process of step S150 for the Compton event, that is, the process of the processing circuit 105 determining the LOR by the determination function 105b based on the incident channel determined in step S134, will be described.

[0104] Before describing the process of step S150, the process of step S134 will be described. In step S134, the processing circuit 105 determines, by the determination function 105b, the second detector 2a associated with the incident channel of the gamma ray 17 among the second detectors 2. The processing circuit 105 then estimates, by the determination function 105b, what process caused the signal values ​​of the second detector 2a and the second detector 2b to be generated. For example, the processing circuit 105 estimates, by the determination function 105b, that the signal value generated in the second detector 2a is a signal value caused by the generation of recoil electrons 19 accompanying Compton scattering generated in the second detector 2a, and that the signal value is a signal value generated by the photoelectric effect of the gamma ray 21 after Compton scattering generated in the second detector 2b. That is, the processing circuit 105, through the decision function 105b, estimates the energy of the gamma ray 20 after the Compton scattering event based on the energy information detected in the second detector 2b, which is a channel other than the incident channel of the second detector 2, and estimates the energy of the recoil electron 19 in the Compton scattering event based on the energy information detected in the second detector 2a, which is the incident channel of the second detector.

[0105] Next, in step S150, the processing circuit 105 estimates the LOR using the determination function 105b based on the number of photons N of Cherenkov light estimated from the signal value obtained by the first detector 1 estimated in step S131, the signal value detected by the second detector 2a, and the energy information of the gamma ray detected by the second detector 2b. For example, the processing circuit 105 estimates, using the determination function 105b, a line connecting the detection elements where the Cherenkov light was detected by the first detector 1 as an initial value of the LOR, and calculates predicted values ​​of the number of photons N of Cherenkov light estimated from the signal value obtained by the first detector 1, the signal value detected by the second detector 2a, and the energy information of the gamma ray detected by the second detector 2b based on the LOR.

[0106] Next, the processing circuit 105, using the decision function 105b, corrects the LOR by comparing the predicted values ​​and actual measured values ​​of the number of photons N of Cherenkov light estimated from the signal value obtained by the first detector 1, the signal value detected by the second detector 2a, and the energy information of gamma rays detected by the second detector 2b, and calculates the LOR after correction as the LOR that best explains the number of photons N of Cherenkov light estimated from the signal value obtained by the first detector 1, the signal value detected by the second detector 2a, and the energy information of gamma rays detected by the second detector 2b.

[0107] That is, the processing circuit identifies Compton scatter events detected by the second detector, and determines, from among the identified Compton scatter events, which events correspond to channels defining the LOR or which events correspond to channels in which Compton scattering occurred, based on the detection results from the first detector.

[0108] As described above, the radiation diagnostic apparatus according to the first embodiment can generate counting information with high time resolution while maintaining energy resolution by generating counting information using the first detector 1 that detects Cherenkov light and the second detector 2 that is a normal detector, but the determination unit that determines the event corresponding to the incident channel among the identified Compton scattering events based on the detection result by the first detector makes it possible to estimate the incident position of the gamma ray during Compton scattering, and makes it possible to estimate the LOR more accurately. This makes it possible to improve the spatial resolution of the PET image.

[0109] Second embodiment In the first embodiment, the first detector 1 is described as detecting Cherenkov light, and no description is given of scintillation light or the like that the first detector 1 may detect due to, for example, Compton scattering or the like occurring in the first detector 1. However, the embodiment is not limited thereto. In the second embodiment, the first detector 1 detects Cherenkov light generated when radiation passes through, and further detects scintillation light. The processing circuit 105 determines an event corresponding to the incident channel based on the Cherenkov light detected by the first detector 1 and the scintillation light detected by the first detector 1 by the decision function 105b, and identifies the Compton scattering event detected by the second detector 2.

[0110] In addition, since a detector used as the first detector 1 for detecting Cherenkov light can often detect scintillation light as well, the first detector 1 used in the first embodiment can also be used as the first detector 1 according to the second embodiment. In the second embodiment, the first timing information acquisition circuit 101 detects the scintillation light from the first detector 1 in addition to the Cherenkov light, and the processing circuit 105 performs processing including the scintillation light detected from the first detector 1.

[0111] The process according to the second embodiment will be described using Figures 8 to 11 while referring again to Figure 6. In Figure 6, the process other than steps S120 to S160 is the same as that of the first embodiment, so repeated description will be omitted.

[0112] As in the first embodiment, in step S120, the processing circuit 105 uses the determination function 105b to identify and extract event information in the first detector 1 based on the Compton scattering event identified in step S105 and geometry information of the PET device 100. Here, in the second embodiment, the first detector 1 detects scintillation light together with Cherenkov light generated when radiation passes through. That is, the processing circuit 105 uses the acquisition function 105f to acquire a detector output signal including a Cherenkov light component and a scintillation light component from the first detector 1 through the first timing information acquisition circuit 101.

[0113] Next, in step S130, the processing circuit 105, using the decision function 105b, estimates the gamma ray incidence position in the second detector 2 based on the event information of the Cherenkov light and the scintillation light in the first detector 1 identified in step S120.

[0114] The process of step S130 in the second embodiment will be described with reference to FIG. 8. FIG. 8 is a flowchart illustrating the process flow of step S130 in the second embodiment. Compared with FIG. 7 illustrating the process flow of step S130 in the first embodiment, the process of step S134 is similar in FIG. 7 and FIG. 8. Instead of the processes of steps S131 to S133 in FIG. 7 in the first embodiment, the process of steps S131A to S133A is performed in the second embodiment. Note that the process of step S134 is similar to that in the first embodiment, and therefore will not be described repeatedly.

[0115] In step S131A, the processing circuit 105, by the decision function 105b, extracts the Cherenkov light component and the scintillation light component from the detector output signal including the Cherenkov light component and the scintillation light component acquired in step S120.

[0116] Fig. 9 shows the signal waveform of the detector output signal output by the detector 1. Signals 30a, 30b, 30c, 30d, 30e, 30f, etc. indicate output signals sampled at each time shown in Fig. 9. The processing circuit 150 performs parameter estimation on the detector output waveform 31 obtained from these signals 30a to 30f, etc., by the decision function 105b using a function F given by the following equation (6), for example.

[0117]

number

[0118] Here, F is the detector output waveform 31, t is time, f(t) is a known function representing the scintillation light component contained in the detector output waveform 31, α is a parameter representing the magnitude of the scintillation light component contained in the detector output waveform 31, g(t) is a known function representing the Cherenkov light component contained in the detector output waveform 31, and β is a parameter representing the magnitude of the Cherenkov light component contained in the detector output waveform 31. In this way, the processing circuit 105 extracts the Cherenkov light component and the scintillation light component by using the decision function 105b to perform parameter estimation of the detector output waveform 31, which is the signal waveform obtained by the first detector 1, as the sum of the Cherenkov light component and the scintillation light component.

[0119] Next, in step S132A, the processing circuit 105, using the decision function 105b, calculates the number of scintillation photons based on the magnitude α of the scintillation light component obtained in step S132B, and calculates the portion of the energy imparted to the first detector 1 by the radiation that is related to the scintillation light based on the calculated number of scintillation photons.

[0120] Next, in step S132B, the calculation function 105b calculates the number of Cherenkov photons N based on the magnitude β of the component of Cherenkov light obtained in step S131A. Next, the processing circuit 105 uses the calculation function 105b to calculate the portion of the energy imparted to the first detector 1 by the radiation that is related to Cherenkov light based on the number of Cherenkov photons N.

[0121] For example, gamma rays have energy E dep The number of Cherenkov photons generated by applying

[0122]

number

[0123] where A is the proportional coefficient that represents the stopping power, α is the fine structure constant (1 / 137), Z is the charge of the charged particle that produces Cherenkov radiation, λ1 and λ2 are the two ends of the visible wavelength of Cherenkov radiation, and n is the refractive index of the medium.

[0124] In addition, β is the relative velocity of the charged particle in the material to the photon velocity in vacuum, and the energy E dep The following equation (8) holds between

[0125]

number

[0126] where m0 is the rest mass of the electron and c is the speed of light.

[0127] By substituting equation (8) into equation (7) and solving the differential equation, the number of Cherenkov photons N and the energy E deposited by the gamma ray on the first detector 1 can be calculated. dep Specifically, the following equation (9) approximately holds:

[0128]

number

[0129] Here, E th is the energy threshold, and γ is a predetermined coefficient. The above formula (9) can be illustrated as in FIG. 10. A graph 40 shows the relationship between the number of Cherenkov photons N and the energy E dep In step S132B, the processing circuit 105 calculates, by the calculation function 105b, the number of Cherenkov photons N and the energy E imparted to the first detector 1. dep Based on the relationship between the number of Cherenkov photons and the number of Cherenkov photons N, the energy E dep Calculate.

[0130] 8, in step S132C, the processing circuit 105, by the calculation function 105b, calculates the energy imparted to the first detector 1. As an example, the processing circuit 150, by the calculation function 105b, calculates the energy imparted to the first detector 1 by summing the part of the energy imparted to the first detector 1 calculated in step S132A that is related to the scintillation light and the part of the energy imparted to the first detector 1 calculated in step S132B that is related to the Cherenkov light.

[0131] Next, in step S133A, the processing circuit 105 uses the calculation function 105b to calculate the scattering angle in the first detection channel based on the energy imparted to the first detector 1 calculated in step S132C. Specifically, the formula (1) which is the law of conservation of energy and the formula (2) which expresses the relationship between the energy before and after Compton scattering and the scattering angle have been described as relating to the second detector 2, but the same formula also applies when Compton scattering occurs in the first detector 1. Therefore, by reinterpreting and applying the above formulas (1) and (2) to the case where similar scattering occurs in the first detector 1, the processing circuit 105 can calculate the scattering angle when Compton scattering occurs in the first detector 1 based on the energy imparted to the first detector 1 calculated in step S132C using the calculation function 105b, and calculates the scattering angle in the first detection channel based on this.

[0132] Next, in step S134, by performing the same process as in the first embodiment, the processing circuit 105 determines the incident channel based on the scattering angle in the first detection channel by the determination function 105b. Thus, in steps S131A to S134, the processing circuit 105 separates the signal waveform obtained by the first detector 1 into a Cherenkov light component and a scintillation light component by the determination function 105b, and determines an event corresponding to the incident channel based on the separated Cherenkov light component and scintillation light component.

[0133] Also, returning to FIG. 6, in step S150, similarly to the first embodiment, the processing circuit 105 determines the LOR by the determination function 105b based on the incident channel determined in step S134.

[0134] Next, in step S160, similar to the first embodiment, the processing circuitry 105 performs processing similar to the image generation procedure of a normal PET device using the image generation function 105c, and generates a medical image based on the LOR estimated in step S150.

[0135] In step S110, among the events detected by the second detector, for events other than those determined by the processing circuit 105 by the identification function 105a to be normal events not involving Compton scattering (step S110 No), the processing circuit 105 identifies event information in the first detector 1 corresponding to the event detected by the second detector by the decision function 105b (step S140). At this time, when identifying the event information in the first detector, the processing circuit 105 may use information on the scintillation light obtained from the first detector 1, or may not use such information in the processing of step S140.

[0136] As described above, in the second embodiment, the Compton scattering event is corrected using both the Cherenkov light and the scintillation light detected by the first detector 1. This makes it possible to improve the spatial resolution of the PET image.

[0137] (Other embodiments) Although some embodiments have been described, the embodiments are not limited thereto. In the embodiments, the processing circuit 105 first identifies an occurrence event of scintillation light in the second detector 2, and then identifies corresponding event information in the first detector 1, but the embodiments are not limited thereto.

[0138] As an example, in a step before step S100 in FIG. 6, the processing circuit 105 identifies event information of the Cherenkov event from the first detector 1 by the acquisition function 105f. Next, the processing circuit 105 identifies event information including a Compton scattering event detected by the second detector, which corresponds to the Cherenkov event acquired by the acquisition function 105f, based on the event information of the Cherenkov event identified from the first detector 1 and the geometry information of the PET device 100 by the identification function 105a. The processing circuit 105 may acquire the identified event information in the second detector by the acquisition function 105b, thereby performing the processing of step S100. In this way, the efficiency of estimating the LOR can be improved by first identifying the event information in the first detector 1, which has excellent time resolution.

[0139] According to at least one of the embodiments described above, image quality can be improved.

[0140] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention.

[0141] Regarding the above embodiment, the following supplementary notes are disclosed as one aspect and optional features of the invention.

[0142] (Appendix 1) a first detector that detects Cherenkov light produced when the radiation passes through; a second detector disposed opposite the first detector on a side farther from a source of the radiation, the second detector detecting energy information of the radiation; An identification unit that identifies a Compton scattering event detected by the second detector; A determination unit that determines an event corresponding to an incident channel among the identified Compton scattering events based on a detection result by the first detector; A radiation diagnostic apparatus comprising:

[0143] (Appendix 2) The identification unit may identify a Compton scattering event based on energy information, time information, and detection channel information of the event detected by the second detector. The determination unit may extract a Cherenkov event corresponding to the identified Compton scattering event based on time information of the event detected by the first detector and detection channel position information of the first detector, and determine the incident channel based on the Cherenkov event.

[0144] (Appendix 3) The determination unit may determine the incident channel based on a detection channel of the first detector in which the Cherenkov event is detected and a scattering angle at the detection channel of the first detector.

[0145] (Appendix 4) The determination unit may estimate a number of Cherenkov photons associated with the Cherenkov event based on data obtained by the first detector, estimate an energy of a recoil electron associated with the Cherenkov event based on the number of Cherenkov photons, and detect the scattering angle based on the energy of the recoil electrons.

[0146] (Appendix 5) The determination unit may determine the incident channel based on a point where a Compton cone that extends from a detection channel of the first detector and corresponds to the scattering angle intersects with the second detector.

[0147] (Appendix 6) The determination unit may estimate the energy of gamma rays after the Compton scattering event based on energy information detected in a channel other than the incident channel of the second detector, and may estimate the energy of recoil electrons in the Compton scattering event based on energy information detected in the incident channel of the second detector.

[0148] (Appendix 7) The apparatus may further include an acquisition unit that acquires a Cerenkov event from the first detector. The identification unit may identify a Compton scattering event detected by the second detector, which corresponds to the Cherenkov event acquired by the acquisition unit.

[0149] (Appendix 8) The determination unit may estimate an LOR based on energy information detected in a channel other than the incident channel, energy information detected in the incident channel, and data obtained by the first detector.

[0150] (Appendix 9) The determination unit may estimate an LOR based on energy information detected in a channel other than the incident channel and data obtained by the first detector.

[0151] (Appendix 10) The determination unit may estimate a LOR based on energy information detected in the entrance channel and data obtained by the first detector.

[0152] (Appendix 11) the first detector further detects scintillation light; The determination unit may determine an event corresponding to the incident channel based on the Cherenkov light and the scintillation light detected by the first detector.

[0153] (Appendix 12) The determination unit may separate a signal waveform obtained by the first detector into a Cherenkov light component and a scintillation light component, and determine an event corresponding to the incident channel based on the separated Cherenkov light component and the scintillation light component.

[0154] (Appendix 13) The determination unit may separate the signal waveform obtained by the first detector into the Cherenkov light component and the scintillation light component by performing parameter estimation using a sum of a Cherenkov light component and a scintillation light component.

[0155] (Appendix 14) The determination unit may identify Compton scatter events detected by the second detector, and determine, from among the identified Compton scatter events, an event corresponding to a channel defining an LOR based on the detection result from the first detector.

[0156] (Appendix 15) The determination unit may identify a Compton scattering event detected by the second detector, and determine, from the identified Compton scattering events, an event corresponding to a channel in which Compton scattering occurred, based on the detection result of the first detector (1).

[0157] (Appendix 16) identifying a Compton scattering event detected by a second detector that is disposed opposite a first detector that detects Cherenkov light generated when the radiation passes through the first detector and detects energy information of the radiation, the second detector being disposed on a side farther from a source of the radiation; determining an event corresponding to an incident channel among the identified Compton scattering events based on a detection result by the first detector; A method for correcting Compton scattering events.

[0158] (Appendix 17) identifying a Compton scattering event detected by a second detector that is disposed opposite a first detector that detects Cherenkov light generated when the radiation passes through the first detector and detects energy information of the radiation, the second detector being disposed on a side farther from a source of the radiation; and causing a computer to execute a process of determining, from the identified Compton scattering events, an event corresponding to an incident channel based on a detection result by the first detector. program.

[0159] (Appendix 18) identifying a Compton scattering event detected by a second detector that is disposed opposite a first detector that detects Cherenkov light generated when the radiation passes through the first detector and detects energy information of the radiation, the second detector being disposed on a side farther from a source of the radiation; A non-transitory computer-readable medium storing a program that causes a computer to execute a process of determining, among the identified Compton scattering events, an event that corresponds to an incident channel based on the detection result at the first detector. [Explanation of symbols]

[0160] 1 First detector 2 Second detector 101 First timing information acquisition circuit 102 Second timing information acquisition circuit 105 Processing circuit 105a Specific Functions 105b Decision function 105c Image Generation Function 105d System control function 105e Bed Control Function 105f acquisition function 105g Calculation Function

Claims

1. a first detector that detects Cherenkov light generated when the radiation passes through; a second detector disposed opposite the first detector on a side farther from a source of the radiation, the second detector detecting energy information of the radiation; an identification unit that identifies a Compton scattering event detected by the second detector; A determination unit that determines an event corresponding to an incident channel from among the identified Compton scattering events based on a detection result by the first detector; A radiation diagnostic apparatus comprising:

2. The identification unit identifies a Compton scattering event based on energy information, time information, and detection channel information of the event detected by the second detector; 2. The radiation diagnostic apparatus according to claim 1, wherein the determination unit extracts a Cherenkov event corresponding to the identified Compton scattering event based on time information of the event detected by the first detector and detection channel position information of the first detector, and determines the incident channel based on the Cherenkov event.

3. The radiation diagnostic apparatus according to claim 2 , wherein the determination unit determines the incident channel based on a detection channel of the first detector in which the Cherenkov event is detected and a scattering angle at the detection channel of the first detector.

4. 4. The radiation diagnostic apparatus according to claim 3, wherein the determination unit estimates a number of Cherenkov photons associated with the Cherenkov event based on data obtained by the first detector, estimates energy of recoil electrons associated with the Cherenkov event based on the number of Cherenkov photons, and detects the scattering angle based on the energy of the recoil electrons.

5. The radiation diagnostic apparatus according to claim 3 , wherein the determination unit determines the incident channel based on a point at which a Compton cone corresponding to the scattering angle, which spreads from a detection channel of the first detector, intersects with the second detector.

6. 4. The radiation diagnostic device according to claim 3, wherein the determination unit estimates the energy of a gamma ray after the Compton scattering event based on energy information detected in a channel other than the incident channel in the second detector, and estimates the energy of a recoil electron in the Compton scattering event based on energy information detected in the incident channel in the second detector.

7. An acquisition unit that acquires a Cherenkov event from the first detector, The radiation diagnostic apparatus according to claim 1 , wherein the identifying unit identifies a Compton scattering event detected by the second detector that corresponds to the Cherenkov event acquired by the acquiring unit.

8. The radiation diagnostic apparatus according to claim 1 , wherein the determination unit estimates a line of response (LOR) based on energy information detected in a channel other than the incident channel and data obtained by the first detector.

9. The radiological diagnostic apparatus according to claim 1 , wherein the determination unit estimates a line of response (LOR) based on energy information detected in the incident channel and data obtained by the first detector.

10. 9. The radiation diagnostic apparatus according to claim 8, wherein the determination unit estimates the LOR (Line Of Response) based on energy information detected in a channel other than the incident channel, energy information detected in the incident channel, and data obtained by the first detector.

11. the first detector further detects scintillation light; The radiation diagnostic apparatus according to claim 1 , wherein the determination unit determines the event corresponding to the incident channel based on the Cherenkov light and the scintillation light detected by the first detector.

12. 12. The radiation diagnostic apparatus according to claim 11, wherein the determination unit separates a signal waveform obtained by the first detector into a Cherenkov light component and a scintillation light component, and determines an event corresponding to the incident channel based on the separated Cherenkov light component and the scintillation light component.

13. The identification unit identifies a Compton scattering event detected by the second detector, The radiation diagnostic apparatus according to claim 1 , wherein the determination unit determines, from the identified Compton scattering events, an event corresponding to a channel that defines an LOR based on a detection result from the first detector.

14. The identification unit identifies a Compton scattering event detected by the second detector, The radiation diagnostic apparatus according to claim 1 , wherein the determination unit determines, from the identified Compton scattering events, an event corresponding to a channel in which Compton scattering has occurred, based on a detection result from the first detector.

15. identifying a Compton scattering event detected by a second detector that is disposed opposite a first detector that detects Cherenkov light generated when the radiation passes through the first detector and detects energy information of the radiation, the second detector being disposed on a side farther from a source of the radiation; determining an event corresponding to an incident channel among the identified Compton scattering events based on a detection result by the first detector; A method for correcting Compton scattering events.

16. identifying a Compton scattering event detected by a second detector that is disposed opposite a first detector that detects Cherenkov light generated when the radiation passes through the first detector and detects energy information of the radiation, the second detector being disposed on a side farther from a source of the radiation; causing a computer to execute a process of determining an event corresponding to an incident channel among the identified Compton scattering events based on a detection result by the first detector; program.

Images