Image acquisition device and image acquisition method

Abstract

To provide an image acquisition device and an image acquisition method with which it is possible to acquire a tomographic image that represents anatomical information of an analyte without carrying out image reconstruction.SOLUTION: An image acquisition device 1A comprises a measurement unit 10 and a processing unit 20. For each simultaneous count event at which a pair of gamma-ray photons generated by paired extinguishment of electrons and positrons in a positron-emitting nuclide 81 is simultaneously counted by a first detector 11 and a second detector 12, the processing unit 20 determines, on the basis of a position and time at which the gamma-ray photons are detected by the first detector 11 and the second detector 12, respectively, and a position of the positron-emitting nuclide 81, a position where the gamma-ray photons are Compton-scattered in the analyte 90, assuming that the gamma-ray photons having arrived at one of the first detector 11 and the second detector 12 have arrived without being Compton-scattered in the analyte 90 and the gamma-ray photons having arrived at the other of these have arrived after being Compton-scattered in the analyte 90.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an image acquisition device and an image acquisition method. [Background technology]

[0002] Nuclear medicine diagnostic devices such as PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography) can acquire tomographic images of subjects who have been administered drugs labeled with positron-emitting or single-photon-emitting radionuclides. The tomographic images acquired by these nuclear medicine diagnostic devices represent the distribution of positron-emitting or single-photon-emitting radionuclides (drug distribution) in the subject and can be used to diagnose the subject's health status.

[0003] X-ray CT scanners can also acquire three-dimensional tomographic images of a subject. The tomographic images acquired by an X-ray CT scanner represent the anatomical information of the subject. Hereafter, tomographic images will be referred to as three-dimensional tomographic images.

[0004] By using PET and X-ray CT scanners in combination, and correcting PET images with anatomical information acquired by the X-ray CT scanner, the image quality of PET images is being improved. However, because X-ray CT scanners are expensive, research and development is underway to create inexpensive devices that can acquire tomographic images representing the anatomical information of the subject.

[0005] Non-patent document 1 and patent document 1 each describe a device capable of acquiring both tomographic images representing the distribution of positron-emitting radionuclides in a subject and tomographic images representing anatomical information.

[0006] The apparatus described in Non-Patent Literature 1 has a PET apparatus configuration in which numerous detectors are arranged around the measurement space where the subject is placed. This apparatus uses detectors having LSO (Lu2SiO5:Ce) scintillators to detect gamma rays with energies of 307 keV or 202 keV emitted from 176 Lu contained in the LSO scintillator of each detector, and the gamma rays that have passed through the subject are detected by other detectors. Then, this apparatus performs image reconstruction processing based on the detection results of gamma rays with energies of 307 keV or 202 keV to obtain a tomographic image representing the anatomical information of the subject.

[0007] The apparatus described in Patent Document 1 utilizes an electron-tracking Compton camera (ETCC). Conventional Compton cameras estimate that gamma rays originated from a position on a conical surface called a Compton cone based on energy information from both the scattering and absorbing materials. In contrast, an ETCC is said to be able to uniquely identify the direction of gamma ray arrival by tracking the tracks of recoil electrons using a gas detector. This apparatus uses an ETCC to detect the direction of arrival of gamma rays that have been Compton-scattered and whose energy has decreased in a subject who has been administered a drug labeled with a positron-emitting nuclide. Then, based on the detection result of the gamma ray arrival direction by the ETCC, the apparatus uses analytical or statistical methods, i.e., image reconstruction processing, to obtain a tomographic image representing the anatomical information of the subject. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 6990412 [Non-patent literature]

[0009] [Non-Patent Document 1] Mohammadreza Teimoorisichani etal., Med. Phys., 2022, vol 49, pages 309-323 [Non-Patent Document 2] Gerard Arino-Estrada, et al.,Phys. Med. Biol., 64 (2019) 175001 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Both Non-Patent Document 1 and Patent Document 1 require image reconstruction processing based on gamma-ray detection results to obtain tomographic images representing the anatomical information of the subject. The tomographic images obtained through this image reconstruction process suffer from reduced image quality and degraded anatomical information due to the image reconstruction process itself.

[0011] The present invention was made to solve the above-mentioned problems, and aims to provide an image acquisition device and an image acquisition method that can acquire tomographic images representing the anatomical information of a subject without performing image reconstruction processing. [Means for solving the problem]

[0012] The image acquisition apparatus of the present invention comprises (1) a measurement unit that includes a first detector and a second detector, each detecting gamma-ray photons, and outputs signals representing the detection position and detection time when the first detector and the second detector each detect gamma-ray photons, and (2) a processing unit that processes the signals output from the first detector and the second detector, respectively. The image acquisition apparatus of the present invention can be configured in the following ways.

[0013] In the first embodiment of the image acquisition device, the measurement unit and processing unit are as follows. In the first measurement mode, the measurement unit outputs signals representing the detection position and detection time of gamma-ray photons by the first and second detectors, respectively, with the subject placed between the first and second detectors and a positron-emitting nuclide placed between the first or second detector and the subject. In the first measurement mode, the processing unit, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in the positron-emitting nuclide, determines whether the gamma-ray photon arriving at one of the first or second detectors arrived without Compton scattering, or whether the gamma-ray photon arriving at the other detector arrived after Compton scattering within the subject, and determines the detection position and detection time of the gamma-ray photons by the first and second detectors, respectively, and the position of the positron-emitting nuclide. The difference in detection times between the first and second detectors is used. Then, the location where the gamma-ray photon was Compton scattered is determined, and a first tomographic image is created that shows the distribution of Compton scattering locations in the subject for each of multiple simultaneous counting events.

[0014] In the second embodiment of the image acquisition device, in addition to the first embodiment, the measurement unit and processing unit are as follows. In the second measurement mode, the measurement unit outputs signals representing the detection position and detection time of gamma-ray photons by the first and second detectors, respectively, with a subject who has been administered a drug labeled with a positron-emitting nuclide placed between the first and second detectors. In the second measurement mode, the processing unit, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in the positron-emitting nuclide, outputs signals representing the detection position and detection time of gamma-ray photons by the first and second detectors, respectively. The difference in detection times between the first and second detectors is used. The first tomography unit determines the location where an annihilation event occurred and creates a second tomographic image representing the distribution of annihilation event locations in the subject for each of multiple simultaneous occurrence events. The second tomographic image is then corrected based on the first tomographic image.

[0015] In a third embodiment of the image acquisition device, the measurement unit and processing unit are as follows: The measurement unit outputs signals representing the detection position and detection time of gamma-ray photons by the first and second detectors, respectively, when a subject who has been administered a drug labeled with a positron-emitting nuclide is placed between the first and second detectors, and the positron-emitting nuclide is placed between the first or second detector and the subject. The processing unit, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in the positron-emitting nuclide, (a) when the gamma-ray photon arriving at one of the first or second detectors arrived without Compton scattering within the subject, and the gamma-ray photon arriving at the other detector arrived after Compton scattering within the subject, the processing unit determines the detection position and detection time of the gamma-ray photons by the first and second detectors, respectively, and the position of the positron-emitting nuclide placed between the first or second detector and the subject. The difference in detection times between the first and second detectors is used. (b) If the gamma-ray photons arrived at both the first and second detectors without Compton scattering, then the detection position and detection time of the gamma-ray photons by the first and second detectors, respectively, are determined. The difference in detection times between the first and second detectors is used. The system then determines the location where an annihilation event occurred. The processing unit then creates a first tomographic image representing the distribution of Compton scattering locations in the subject obtained for each of the multiple simultaneous counting events, creates a second tomographic image representing the distribution of annihilation event locations in the subject obtained for each of the multiple simultaneous counting events, and corrects the second tomographic image based on the first tomographic image.

[0016] In the fourth aspect of the image acquisition device, in addition to the aspects of the second or third aspect, the positron-emitting radionuclide placed between the first or second detector and the subject and the positron-emitting radionuclide used to label the drug administered to the subject are of the same type.

[0017] In a fifth aspect of the image acquisition apparatus, in addition to any one of the first to fourth aspects, the processing unit determines whether the gamma ray photons arriving at the first detector or the second detector have undergone Compton scattering based on one or more of the position of the positron-emitting nuclide, the energy level of the gamma ray photons, and the detection time of the gamma ray photons respectively by the first detector and the second detector.

[0018] In a sixth aspect of the image acquisition apparatus, in addition to any one of the first to fifth aspects, the measurement unit outputs a signal representing the detection position and detection time of gamma ray photons respectively by the first detector and the second detector in a state where a positron-emitting nuclide is placed between the first detector and the subject and a positron-emitting nuclide is also placed between the second detector and the subject.

[0019] In a seventh aspect of the image acquisition apparatus, in addition to any one of the first to sixth aspects, the measurement unit outputs a signal representing the detection position and detection time of gamma ray photons respectively by the first detector and the second detector in a state where the detection surface of the first detector is narrower than the detection surface of the second detector and a positron-emitting nuclide is placed between the first detector and the subject.

[0020] In an eighth aspect of the image acquisition apparatus, in addition to any one of the first to seventh aspects, the measurement unit further comprises a shield that prevents gamma ray photons backscattered by either one of the first detector and the second detector from being incident on the other.

[0021] In a ninth aspect of the image acquisition apparatus, in addition to any one of the first to eighth aspects, the measurement unit further comprises a moving unit that moves the positron-emitting nuclide between the first detector or the second detector and the subject.

[0022] The image acquisition method of the present invention comprises (1) a measurement step in which a first detector and a second detector, each detecting gamma-ray photons, output signals representing the detection position and detection time when the first detector and the second detector each detect a gamma-ray photon, and (2) a processing step in which signals output from the first detector and the second detector are processed. The image acquisition method of the present invention can take the following forms.

[0023] In the first embodiment of the image acquisition method, the measurement step and processing step are as follows. In the measurement step, in the first measurement mode, the subject is placed between the first detector and the second detector, and a positron-emitting nuclide is placed between the first detector or the second detector and the subject, and signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector are output. In the processing step, in the first measurement mode, for each simultaneous counting event in which the first detector and the second detector simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in the positron-emitting nuclide, it is assumed that the gamma-ray photon arriving at one of the first detectors arrived without Compton scattering within the subject, and the gamma-ray photon arriving at the other detector arrived after Compton scattering within the subject, and based on the detection position and detection time of the gamma-ray photon by the first detector and the second detector, and the position of the positron-emitting nuclide, The difference in detection times between the first and second detectors is used. Then, the location where gamma-ray photons were Compton scattered within the subject is determined, and a first tomographic image is created that represents the distribution of Compton scattering locations in the subject for each of multiple simultaneous counting events.

[0024] In the second aspect of the image acquisition method, in addition to the first aspect, the measurement step and processing step are as follows. In the measurement step, in the second measurement mode, with a subject who has been administered a drug labeled with a positron-emitting nuclide placed between the first detector and the second detector, signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector are output. In the processing step, in the second measurement mode, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated in the subject by an electron-positron annihilation event in the positron-emitting nuclide, the detection position and detection time of the gamma-ray photons by the first and second detectors are used to process the data. The difference in detection times between the first and second detectors is used. The first step involves determining the location where an annihilation event occurred and creating a second tomographic image that represents the distribution of annihilation event locations in the subject for each of multiple simultaneous occurrence events. The second tomographic image is then corrected based on the first tomographic image.

[0025] In the third aspect of the image acquisition method, the measurement step and processing step are as follows. In the measurement step, a subject who has been administered a drug labeled with a positron-emitting nuclide is placed between the first detector and the second detector, and with the positron-emitting nuclide placed between the first detector or the second detector and the subject, signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector are output. In the processing step, for each simultaneous counting event in which the first detector and the second detector simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in the positron-emitting nuclide, (a) if the gamma-ray photon arriving at one of the first detector or the second detector arrived without Compton scattering within the subject, and the gamma-ray photon arriving at the other detector arrived after Compton scattering within the subject, the detection position and detection time of the gamma-ray photons by the first detector and the second detector, respectively, and the position of the positron-emitting nuclide placed between the first detector or the second detector and the subject are determined. The difference in detection times between the first and second detectors is used.(b) If the gamma-ray photons arrived at both the first and second detectors without Compton scattering within the subject, then, based on the detection position and detection time of the gamma-ray photons by the first and second detectors, The difference in detection times between the first and second detectors is used. The first step is to determine the location where an annihilation event occurred. The processing step then creates a first tomographic image representing the distribution of Compton scattering locations in the subject obtained for each of the multiple simultaneous counting events, creates a second tomographic image representing the distribution of annihilation event locations in the subject obtained for each of the multiple simultaneous counting events, and corrects the second tomographic image based on the first tomographic image.

[0026] In the fourth aspect of the image acquisition method, in addition to the aspects of the second or third aspect, the positron-emitting radionuclide placed between the first or second detector and the subject and the positron-emitting radionuclide used to label the drug administered to the subject are of the same type.

[0027] In the fifth aspect of the image acquisition method, in addition to any of the first to fourth aspects, the processing step determines whether or not a gamma-ray photon arriving at the first or second detector has undergone Compton scattering within the sample, based on one or more of the following: the position of the positron-emitting nuclide, the magnitude of the gamma-ray photon's energy, and the detection time of the gamma-ray photon by the first and second detectors, respectively.

[0028] In the sixth aspect of the image acquisition method, in addition to any of the first to fifth aspects, the measurement step involves placing a positron-emitting nuclide between the first detector and the subject, and also placing a positron-emitting nuclide between the second detector and the subject, and outputting signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector, respectively.

[0029] In the seventh aspect of the image acquisition method, in addition to any of the first to sixth aspects, the measurement step involves using a first detector with a narrower detection surface than the second detector, and with a positron-emitting nuclide placed between the first detector and the subject, the first and second detectors each output signals representing the detection position and time of gamma-ray photons.

[0030] In the eighth aspect of the image acquisition method, in addition to any of the first to seventh aspects, the measurement step includes a shield to prevent gamma-ray photons that have been backscattered from either the first detector or the second detector from entering the other.

[0031] In the ninth aspect of the image acquisition method, in addition to any of the first to eighth aspects, the measurement step involves moving a positron-emitting nuclide between the first or second detector and the sample. [Effects of the Invention]

[0032] According to the present invention, tomographic images representing the anatomical information of a subject can be obtained without performing image reconstruction processing. [Brief explanation of the drawing]

[0033] [Figure 1] Figure 1 is a diagram showing the configuration of the image acquisition device 1A of the first embodiment (particularly illustrating the acquisition of the first tomographic image using the first measurement mode). [Figure 2] Figure 2 illustrates a method for determining the location of Compton scattering of gamma-ray photons within a test subject. [Figure 3] Figure 3 shows the configuration of the image acquisition device 1A of the first embodiment (particularly illustrating the acquisition of the second tomographic image using the second measurement mode). [Figure 4] Figure 4 shows the configuration of the image acquisition device 1B according to the second embodiment. [Figure 5] Figure 5 shows the configuration of the image acquisition device 1C according to the third embodiment. [Figure 6] Figure 6 shows the configuration of the image acquisition device 1D according to the fourth embodiment. [Figure 7] Figure 7 shows the configuration of the image acquisition device 1E according to the fifth embodiment. [Figure 8] Figure 8 shows the configuration of the image acquisition device 1F according to the sixth embodiment. [Figure 9] Figures 9(a) and 9(b) illustrate the change in the field of view of the device when the positron-emitting nuclide 81 is moved in a direction parallel to the detection surface of the first detector 11 in the measurement section 10F of the image acquisition device 1F of the sixth embodiment. [Figure 10] Figures 10(a) and 10(b) illustrate the image quality of the first tomographic image when the positron-emitting nuclide 81 is moved in a direction perpendicular to the detection surface of the first detector 11 in the measurement unit 10F of the image acquisition device 1F of the sixth embodiment. [Figure 11] Figure 11 shows the configuration and arrangement of the measurement unit as assumed in the simulation. [Figure 12] Figure 12 shows the configuration of the phantom assumed to be subject 90 in the simulation. [Figure 13] Figure 13 shows the first tomographic image obtained from the simulation. [Modes for carrying out the invention]

[0034] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. The present invention is not limited to these examples, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0035] (First Embodiment) Figure 1 shows the configuration of an image acquisition device 1A according to the first embodiment. The image acquisition device 1A comprises a measurement unit 10, a processing unit 20, and a display unit 30. The measurement unit 10 includes a first detector 11 and a second detector 12 arranged opposite each other with the subject 90 in between. The first detector 11 and the second detector 12 each detect gamma-ray photons and output signals representing the detection position and detection time when gamma-ray photons are detected. The processing unit 20 processes the signals output from the first detector 11 and the second detector 12 to create a tomographic image of the subject 90. The display unit 30 displays the tomographic image and the like created by the processing unit 20. The processing unit 20 and the display unit 30 may be configured by, for example, a computer.

[0036] For example, Cherenkov detectors are used as the first detector 11 and the second detector 12, respectively. The Cherenkov detector consists of a Cherenkov radiator (e.g., lead glass, lead fluoride PbF2, hafnium oxide HfO2, etc.) and a microchannel plate-integrated photomultiplier tube (MCP-PMT). The Cherenkov detector may be, for example, a two-dimensional array of small units, each lacking position detection capability, or it may be a configuration combining a Cherenkov radiator and a multi-anode MCP-PMT.

[0037] Furthermore, the Cherenkov detector uses BGO(Bi4Ge3O 12 A low-energy scintillator, such as a ) can be used as a Cherenkov radiator. Low-energy scintillators interact with gamma rays, first emitting Cherenkov light and then scintillation light, so they can be used as Cherenkov radiators and achieve high temporal resolution. This makes it possible to construct a detector that is less expensive than LSO scintillators, etc.

[0038] Furthermore, the first detector 11 and the second detector 12 may each be, for example, high-time-resolution semiconductor detectors. A high-time-resolution semiconductor detector may, for example, use thallium bromide (TlBr) and be equipped with an electrode for charge collection and a high-time-resolution photodetector. For example, it may be the one described in Non-Patent Document 2. By using semiconductor detectors, it is expected that the energy resolution will be improved, and as a result, the ability to remove scattering components will be improved, and the image quality will be improved.

[0039] Considering that the spatial resolution of tomographic images acquired by nuclear medicine diagnostic devices such as PET scanners is approximately 3-5 mm, it is desirable that the spatial resolution required for the first detector 11 and the second detector 12 be equivalent to or better than that. Similarly, it is desirable that the temporal resolution required for the first detector 11 and the second detector 12 be 20-35 ps or less in terms of simultaneous time interval resolution.

[0040] If the first detector 11 and the second detector 12 include a Cherenkov radiator or scintillator, it is preferable that they output signals representing the location (detection location) and time (detection time) at which gamma rays interacted with the Cherenkov radiator or scintillator, rather than the location and time at which Cherenkov light or scintillation light was detected. In this case, the detection location is represented by three-dimensional coordinate values ​​that specify not only the location in two directions parallel to the detection surface of the detector, but also the location in a perpendicular direction.

[0041] The detection surfaces of the first detector 11 and the second detector 12 are preferably larger than the subject 90 (or the region of interest within the subject 90). For example, in the case of an image acquisition device that acquires tomographic images of a human brain, the detection surfaces of the first detector 11 and the second detector 12 are preferably about the same size as, or larger than, the human brain.

[0042] The image acquisition device 1A and the image acquisition method using it acquire a tomographic image (first tomographic image) of the subject 90 in a first measurement mode. The image acquisition device 1A and the image acquisition method can also acquire a tomographic image (second tomographic image) of the subject 90 in a second measurement mode. The first tomographic image is an image representing the distribution of Compton scattering locations in the subject 90 and represents anatomical information of the subject 90. The second tomographic image represents the distribution of positron-emitting radionuclides (distribution of drugs) in the subject 90 and can be used to diagnose the health status of the subject 90.

[0043] The acquisition of the first tomographic image using the first measurement mode is performed by the following first measurement step and first processing step. Figure 1 is a diagram showing the configuration of the image acquisition device 1A of the first embodiment, and in particular is a diagram illustrating the acquisition of the first tomographic image using the first measurement mode.

[0044] In the first measurement step, the subject 90 is placed between the first detector 11 and the second detector 12. At this time, the subject 90 does not need to have been administered a positron-emitting nuclide. A positron-emitting nuclide 81 is placed between the first detector 11 or the second detector 12 and the subject 90. It is preferable to use the smallest possible positron-emitting nuclide 81. In this figure, the positron-emitting nuclide 81 is placed between the first detector 11 and the subject 90. The positron emitted from the positron-emitting nuclide 81 immediately annihilates with a nearby electron, and this electron-positron annihilation event produces a pair of gamma-ray photons flying in opposite directions. When the first detector 11 and the second detector 12 detect gamma rays, they each output a signal indicating the detection location and time of the gamma-ray photons.

[0045] In the first processing step, the processing unit 20 determines the location where the gamma-ray photon was Compton scattered based on the detection position and time of the gamma-ray photon by the first detector 11 and the second detector 12, respectively, and the position of the positron-emitting nuclide 81. This is done for each simultaneous counting event in which the first detector 11 and the second detector 12 simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in the positron-emitting nuclide 81. The gamma-ray photon that arrived at one of the first detector 11 and the second detector 12 arrived without Compton scattering within the sample, and the gamma-ray photon that arrived at the other arrived after Compton scattering within the sample.

[0046] The processing unit 20 then creates a first tomographic image representing the distribution of Compton scattering locations in the subject 90 obtained for each of the multiple simultaneous counting events. This first tomographic image represents the anatomical information of the subject 90.

[0047] The processing unit 20 can determine whether or not a gamma-ray photon arriving at the first detector 11 or the second detector 12 has undergone Compton scattering based on one or more of the following: the position of the positron-emitting nuclide 81, the energy of the gamma-ray photon, and the detection time of the gamma-ray photon by the first detector 11 and the second detector 12, respectively. As shown in Figure 1, if the positron-emitting nuclide 81 is placed between the first detector 11 and the subject 90, it can be determined that the gamma rays arriving at the first detector 11 have not undergone Compton scattering within the subject. The energy of a pair of gamma-ray photons generated by electron-positron annihilation is 511 keV, but since the energy of the gamma rays is reduced by Compton scattering, it can be determined whether or not it has undergone Compton scattering based on the energy of the gamma rays. It can also be determined whether or not it has undergone Compton scattering within the subject based on the chronological relationship of the detection times of the gamma-ray photons by the first detector 11 and the second detector 12, respectively.

[0048] Figure 2 illustrates a method for determining the location of Compton scattering of gamma-ray photons within a sample. Let P be the position of the positron-emitting nuclide 81, R1 be the gamma-ray detection position by the first detector 11, R2 be the gamma-ray detection position by the second detector 12, and C be the location of Compton scattering of the gamma-ray. Let t1 be the time of gamma-ray detection by the first detector 11, and t2 be the time of gamma-ray detection by the second detector 12. Of the pair of gamma-ray photons produced by the electron-positron annihilation event in the positron-emitting nuclide 81, the flight distance of one gamma-ray is the distance d1 from position P to position R1. The flight distance of the other gamma-ray is the distance d from position P to position C. 21 And the distance d from position C to position R2 22 The sum of (d 21 +d 22 )

[0049] The difference in flight distance of a pair of gamma-ray photons (d 21 +d 22 -d1) is equal to the difference in detection times of these gamma-ray photons (t2 - t1) multiplied by the speed of light c. Also, the line segment connecting position P and position R1 and the line segment connecting position P and position C are parallel to each other. From the above, based on the detection position R1 and detection time t1 of the gamma-ray photon by the first detector 11, the detection position R2 and detection time t2 of the gamma-ray photon by the second detector 12, and the position P of the positron-emitting nuclide 81, the position C where the gamma-ray photon was Compton scattered can be determined.

[0050] If neither of the pair of gamma-ray photons undergoes Compton scattering, the Compton scattering location determined by the method described in Figure 2 coincides with the location P of positron-emitting nuclide 81. Since this location is outside the subject 90, it can be easily excluded.

[0051] The acquisition of the second tomographic image using the second measurement mode is performed by the following second measurement step and second processing step. Figure 3 is a diagram showing the configuration of the image acquisition device 1A of the first embodiment, and in particular, it is a diagram illustrating the acquisition of the second tomographic image using the second measurement mode.

[0052] In the second measurement step, a subject 90, which has been administered a drug labeled with a positron-emitting nuclide 83, is placed between the first detector 11 and the second detector 12. At this time, the positron-emitting nuclide does not need to be placed outside the subject 90. Due to the electron-positron annihilation event in the positron-emitting nuclide 83 that labels the drug administered to the subject 90, a pair of gamma-ray photons flying in opposite directions are produced. When the first detector 11 and the second detector 12 detect gamma rays, they each output signals indicating the detection location and time of the gamma-ray photons.

[0053] In the second measurement step, the positron-emitting nuclide 83 used to label the drug administered to the subject 90 is preferably of the same type as the positron-emitting nuclide 81 placed between the first detector 11 and the subject 90 in the first measurement step. By using the same type of positron-emitting nuclide 83 and positron-emitting nuclide 81, only one type of positron-emitting nuclide is needed, thus simplifying the measurement preparation. Note that positron-emitting nuclide 81 may also be a calibration positron-emitting nuclide such as 68Ge / 68Ga.

[0054] In the second processing step, the processing unit 20 determines the location where an annihilation event occurred for each simultaneous counting event in which the first detector 11 and the second detector 12 simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in the positron-emitting nuclide 83, based on the detection position and detection time of the gamma-ray photons by the first detector 11 and the second detector 12, respectively. The location where the annihilation event occurred for each simultaneous counting event can be determined based on the difference in the detection times of the gamma-ray photons by the first detector 11 and the second detector 12, on a line segment connecting the detection positions of the gamma-ray photons by the first detector 11 and the second detector 12, respectively.

[0055] The processing unit 20 then creates a second tomographic image representing the distribution of annihilation event locations in the subject 90, obtained for each of the multiple simultaneous counting events. Because the time resolution of the first detector 11 and the second detector 12 is good, the second tomographic image, which is a three-dimensional tomographic image, can be obtained without image reconstruction processing. This second tomographic image represents the distribution of positron-emitting radionuclides 83 (drug distribution) in the subject 90 and can be used to diagnose the health status of the subject 90. The processing unit 20 can further correct the second tomographic image based on the first tomographic image to obtain a second tomographic image corrected for the gamma-ray absorption distribution in the subject 90.

[0056] The acquisition of the first tomographic image using the first measurement mode and the acquisition of the second tomographic image using the second measurement mode may be performed in any order. However, if the acquisition of the second tomographic image using the second measurement mode is performed first, the annihilation event of the positron-emitting nuclide 83 administered to the subject 90 at that time may affect the subsequent acquisition of the first tomographic image using the first measurement mode. Therefore, it is preferable to acquire the first tomographic image using the first measurement mode first.

[0057] In this embodiment, a tomographic image (first tomographic image) representing the anatomical information of the subject 90 can be obtained without image reconstruction processing, thus avoiding a decrease in image quality caused by image reconstruction processing and preventing degradation of anatomical information. Furthermore, a tomographic image (second tomographic image) representing the distribution of positron-emitting radionuclides (drug distribution) in the subject can be obtained without image reconstruction processing.

[0058] In this embodiment, a large-scale rotating mechanism like that of an X-ray CT scanner is unnecessary, allowing for a smaller and less expensive device. Furthermore, compared to using an X-ray CT scanner, this embodiment can reduce the radiation exposure of the subject.

[0059] The apparatus described in Non-Patent Document 1 has a PET apparatus configuration in which numerous detectors are arranged around the measurement space where the subject is placed, making miniaturization difficult. Furthermore, it is difficult to reduce the cost because it uses an LSO scintillator containing the rare material lutetium (Lu). In contrast, this embodiment does not have these problems and enables miniaturization and cost reduction.

[0060] The apparatus described in Patent Document 1 uses a gas detector, making it difficult to improve detection efficiency. In contrast, this embodiment does not have this problem and makes it possible to improve detection efficiency.

[0061] (Second Embodiment) Figure 4 shows the configuration of the image acquisition device 1B of the second embodiment. The image acquisition device 1B comprises a measurement unit 10, a processing unit 20, and a display unit 30. Compared with the first embodiment, the second embodiment differs in that it determines the Compton scattering position and the annihilation event occurrence position in the subject 90 within a common period.

[0062] In the measurement step, a subject 90, which has been administered a drug labeled with positron-emitting nuclide 83, is placed between the first detector 11 and the second detector 12. Additionally, a positron-emitting nuclide 81 is placed between the first detector 11 or the second detector 12 and the subject 90. In this figure, the positron-emitting nuclide 81 is placed between the first detector 11 and the subject 90. By using the same type of positron-emitting nuclide 83 to label the drug administered to the subject 90 and the same type of positron-emitting nuclide 81 placed between the first detector 11 and the subject 90, only one type of positron-emitting nuclide is needed, simplifying the measurement preparation. Note that the positron-emitting nuclide 81 may be a calibration positron-emitting nuclide such as 68Ge / 68Ga. Electron-positron annihilation events in positron-emitting nuclide 81 and positron-emitting nuclide 83 generate a pair of gamma-ray photons flying in opposite directions. When the first detector 11 and the second detector 12 detect a gamma ray, they each output a signal representing the detection location and time of the gamma ray photon.

[0063] In the processing step, the processing unit 20 performs the following processing for each simultaneous counting event in which the first detector 11 and the second detector 12 simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in positron-emitting nuclide 81 or positron-emitting nuclide 83.

[0064] The processing unit 20 determines whether or not a gamma-ray photon arriving at the first detector 11 or the second detector 12 has undergone Compton scattering, based on one or more of the following: the position of the positron-emitting nuclide 81, the energy of the gamma-ray photon, and the detection time of the gamma-ray photon by the first detector 11 and the second detector 12, respectively.

[0065] Based on the above determination, if the gamma-ray photon arriving at one of the first detector 11 and the second detector 12 arrived without Compton scattering within the sample, and the gamma-ray photon arriving at the other arrived after Compton scattering within the sample, the processing unit 20 assumes that the pair of gamma-ray photons arrived from a positron-emitting nuclide 81 outside the sample 90, and uses the calculation explained with reference to Figure 2 to determine the location where the gamma-ray photon was Compton-scattered within the sample 90, based on the detection position and detection time of the gamma-ray photon by the first detector 11 and the second detector 12 respectively, and the position of the positron-emitting nuclide 81.

[0066] On the other hand, if the gamma-ray photons that arrived at both the first detector 11 and the second detector 12 arrived within the sample without Compton scattering, the processing unit 20 assumes that the pair of gamma-ray photons arrived from the positron-emitting nuclide 83 within the sample 90, and determines the location where the annihilation event occurred in the sample 90 based on the detection position and detection time of the gamma-ray photons by the first detector 11 and the second detector 12, respectively.

[0067] Then, after performing the above processing on multiple simultaneous counting events, the processing unit 20 creates a first tomographic image representing the distribution of Compton scattering locations in the subject 90, and a second tomographic image representing the distribution of annihilation event locations in the subject 90. The first tomographic image represents the anatomical information of the subject 90. The second tomographic image represents the distribution of positron-emitting radionuclides 83 (drug distribution) in the subject 90 and can be used to diagnose the health status of the subject 90. Furthermore, by correcting the second tomographic image based on the first tomographic image, the processing unit 20 can obtain a second tomographic image after correcting the gamma-ray absorption distribution in the subject 90.

[0068] In the second embodiment, in addition to achieving the same effects as in the first embodiment, the Compton scattering position and the annihilation event occurrence position in the subject 90 can be determined within a common period, thus shortening the time required to restrain the subject 90.

[0069] (Third embodiment) Figure 5 shows the configuration of the image acquisition device 1C of the third embodiment. The image acquisition device 1C comprises a measurement unit 10, a processing unit 20, and a display unit 30. Compared with the previous embodiments, the third embodiment differs in that a positron-emitting nuclide 81 is placed between the first detector 11 and the subject 90, and a positron-emitting nuclide 82 is also placed between the second detector 12 and the subject 90. It is preferable that the positron-emitting nuclide 81 and the positron-emitting nuclide 82 are of the same type.

[0070] The processing unit 20 determines whether a gamma-ray photon arriving at the first detector 11 or the second detector 12 has undergone Compton scattering, and whether the gamma-ray photon originated from either the positron-emitting nuclide 81 or 82, based on one or more of the following: the position of the positron-emitting nuclides 81 and 82, the magnitude of the gamma-ray photon's energy, and the detection time of the gamma-ray photon by the first detector 11 and the second detector 12, respectively. Based on the determination result, the processing unit 20 determines the position where the gamma-ray photon underwent Compton scattering in the sample 90.

[0071] In this embodiment, the positron-emitting nuclides 81 and 82 can be arranged symmetrically with respect to the sample 90, thereby enabling the acquisition of a higher-quality first tomographic image. Furthermore, since the number of Compton scattering events per unit time in the sample 90 increases, the measurement time can be shortened.

[0072] (Fourth Embodiment) Figure 6 shows the configuration of the image acquisition device 1D of the fourth embodiment. The image acquisition device 1D includes a measurement unit 10D, a processing unit 20, and a display unit 30. Compared with the previous embodiments, the image acquisition device 1D of the fourth embodiment differs in that it includes a measurement unit 10D instead of the measurement unit 10.

[0073] The measurement unit 10D includes a first detector 11D and a second detector 12. The detection surface of the first detector 11D is narrower than that of the second detector 12. A positron-emitting nuclide 81 is placed between the first detector 11D and the sample 90. The first detector 11D and the second detector 12 each output a signal indicating the detection position and time when they detect a gamma-ray photon.

[0074] To acquire the first tomographic image, one of the pair of gamma-ray photons produced by the electron-positron annihilation event in the positron-emitting nuclide 81 must be incident on the first detector 11D and the other on the subject 90 (or the region of interest within the subject 90). As long as this condition is met, the detection surface of the first detector 11D can be narrowed. The closer the position of the positron-emitting nuclide 81 is to the first detector 11D, the narrower the detection surface of the first detector 11D can be. In this way, the first detector 11D can be made small, and the image acquisition device 1D can be constructed at a low cost.

[0075] (Fifth embodiment) Figure 7 shows the configuration of the image acquisition device 1E according to the fifth embodiment. The image acquisition device 1E includes a measurement unit 10E, a processing unit 20, and a display unit 30. Compared to the previous embodiments, the image acquisition device 1E of the fifth embodiment differs in that it includes a measurement unit 10E instead of the measurement unit 10.

[0076] The measurement unit 10E includes a shielding body 13 in addition to the first detector 11 and the second detector 12. The shielding body 13 prevents gamma-ray photons backscattered from either the first detector 11 or the second detector 12 from entering the other. The shielding body 13 is positioned between the first detector 11 and the second detector 12, in a location that does not interfere with the measurement of the Compton scattering position in the subject 90 and the measurement of the annihilation event occurrence position in the subject 90. The shielding body 13 is preferably a plate-shaped material made of a high-density material (e.g., lead) that can block gamma rays.

[0077] (Sixth Embodiment) Figure 8 shows the configuration of the image acquisition device 1F according to the sixth embodiment. The image acquisition device 1F comprises a measurement unit 10F, a processing unit 20, and a display unit 30. Compared to the previous embodiments, the image acquisition device 1F of the sixth embodiment differs in that it includes a measurement unit 10F instead of the measurement unit 10.

[0078] The measurement unit 10F includes a first detector 11 and a second detector 12, as well as a moving unit 14. The moving unit 14 moves the positron-emitting nuclide 81 between the first detector 11 or the second detector 12 and the test subject 90. The moving unit 14 may move the positron-emitting nuclide 81 continuously over time, or it may move it to sequentially position the positron-emitting nuclide 81 at separated positions. The processing unit 20 constantly keeps track of the position of the positron-emitting nuclide 81 in order to determine the position where gamma-ray photons are Compton scattered in the test subject 90.

[0079] The direction of movement of the positron-emitting nuclide 81 may be one or two directions parallel to the detection surface of the first detector 11 or the second detector 12, or it may be perpendicular to the detection surface, or it may be three directions including directions parallel and perpendicular to the detection surface. Moving the positron-emitting nuclide 81 in a direction parallel to the detection surface can expand or homogenize the field of view of the device. Moving the positron-emitting nuclide 81 in a direction perpendicular to the detection surface can improve the image quality of the acquired first tomographic image.

[0080] Figure 9 illustrates the change in the field of view of the device when the positron-emitting nuclide 81 is moved in a direction parallel to the detection surface of the first detector 11 in the measurement unit 10F of the image acquisition device 1F of the sixth embodiment. In this figure, the field of view of the device is indicated by the hatched area. As shown in Figure 9(a), when the positron-emitting nuclide 81 is near the center of the detection surface of the first detector 11, both ends of the subject 90 may be outside the field of view. In contrast, as shown in Figure 9(b), when the positron-emitting nuclide 81 is on the first end side of the detection surface of the first detector 11 (the side slightly to the left of the center in the figure), the first end of the subject 90 is in the field of view, but the second end of the subject 90 (the side slightly to the right of the center in the figure) may be far outside the field of view. Conversely, when the positron-emitting nuclide 81 is on the second end side of the detection surface of the first detector 11, the second end of the subject 90 is in the field of view, but the first end of the subject 90 may be far outside the field of view. In this way, by moving the positron-emitting nuclide 81 in a direction parallel to the detection surface of the first detector 11, the field of view of the device can be expanded or made more uniform.

[0081] Figure 10 illustrates the image quality of the first tomographic image when the positron-emitting nuclide 81 is moved perpendicular to the detection surface of the first detector 11 in the measurement unit 10F of the image acquisition device 1F of the sixth embodiment. In this figure, the position of the positron-emitting nuclide 81 is denoted as P, the gamma ray detection position by the first detector 11 as R1, the gamma ray detection position by the second detector 12 as R2, and the position where the gamma ray was Compton scattered as C. The error range of the line segment connecting position P and position R1, and the error range of the line segment connecting position P and position C are shown as hatched regions.

[0082] Since there is an error in the spatial resolution of the gamma ray detection position R1 by the actual first detector 11, this causes an error in estimating the line segment connecting position P and position R1, and further, an error in estimating the line segment connecting position P and position C, ultimately resulting in an error in estimating position C. As shown in Figure 10(a), the longer the distance between position P and position C, the larger the estimation error of position C, and as shown in Figure 10(b), the shorter the distance between position P and position C, the smaller the estimation error of position C. Therefore, in order to improve the image quality of the acquired first tomographic image, it is preferable to place the positron-emitting nuclide 81 in a position close to the subject 90.

[0083] Since the size and shape of the subject 90 vary, it is preferable to move the positron-emitting nuclide 81 in three directions so as to expand or homogenize the field of view of the device according to the size and shape of the subject 90, and to improve the image quality of the acquired first tomographic image.

[0084] (Simulation example) Next, we will explain the simulation conditions and results for acquiring the first tomographic image of the subject (an image representing the distribution of Compton scattering locations in the subject), as explained using Figures 1 and 2. Here, we used Geant4, which can simulate the trajectories of particles in a material using the Monte Carlo method.

[0085] Figure 11 shows the configuration and arrangement of the measurement unit as assumed in the simulation. The first detector 11 and the second detector 12 each measure 100 × 100 × 5 mm. 3 The Cherenkov detector included a Cherenkov emitter of a certain size. The temporal and spatial resolutions of gamma-ray detection by the first detector 11 and the second detector 12 were both assumed to be ideally 0. The first detector 11 and the second detector 12 were positioned parallel to each other, separated by a distance of 90 mm. A cylindrical phantom with a diameter of 30 mm and a height of 30 mm was assumed and designated as the subject 90. The subject 90 was placed in the center between the first detector 11 and the second detector 12, such that the central axis of the cylinder of the subject 90 was perpendicular to the detection surfaces of the first detector 11 and the second detector 12. A positron-emitting nuclide 81 was placed in the center between the first detector 11 and the subject 90. The size of the positron-emitting nuclide 81 was ignored.

[0086] Figure 12 shows the configuration of the phantom assumed to be the subject 90 in the simulation. This figure shows the phantom as the cylindrical subject 90 viewed along the central axis. The subject 90 is assumed to have cylindrical regions 91, 92, 93, and 94 with a diameter of 3 mm extending in a direction parallel to the central axis of the cylinder, and these are covered by a cylindrical region 95 with a diameter of 30 mm. There are three of each of regions 91, 92, 93, and 94. Region 91 is assumed to be a region made of iodine (atomic number 53). Region 92 is assumed to be a region made of air. Region 93 is assumed to be a region made of gadolinium (atomic number 64). Region 94 is assumed to be a region made of BGO as an example of a heavy substance. Region 95 is assumed to be a region made of water.

[0087] FIG. 13 is a diagram showing a first tomographic image obtained by simulation. This diagram is an image of a cross section perpendicular to the central axis of a phantom as the cylindrically shaped subject 90. In this diagram, the Compton scattering occurrence frequency is represented by shading, where a higher Compton scattering occurrence frequency results in a lighter color. As shown in this diagram, the first tomographic image obtained by simulation indicates that the Compton scattering occurrence frequency is high in the order of region 94 (BGO), region 93 (gadolinium), region 91 (iodine), region 95 (water), and region 92 (air).

[0088] As described above, it was confirmed that the first tomographic image (FIG. 13) representing the distribution of Compton scattering positions in a subject can be acquired. The probability of Compton scattering occurrence in a substance is proportional to the atomic number of the substance. Therefore, the first tomographic image shows the absorption coefficient μ of Compton scattering Compton it can be said that it represents the distribution of .

[0089] (Modified Example) The present invention is not limited to the above embodiments, and various modifications are possible. For example, the configurations of any two or more of the above embodiments may be combined. Description of Reference Signs

[0090] 1A to 1F…image acquisition apparatus, 10, 10D, 10E, 10F…measurement unit, 11, 11D…first detector, 12…second detector, 13…shield, 14…moving unit, 20…processing unit, 30…display unit, 81, 82, 83…positron-emitting nuclide, 90…subject.

Claims

1. A measuring unit includes a first detector and a second detector, each detecting gamma-ray photons, and outputs signals representing the detection position and detection time when the first detector and the second detector each detect a gamma-ray photon. A processing unit that processes the signals output from the first detector and the second detector, respectively, Equipped with, In the first measurement mode, the measurement unit outputs signals representing the detection position and time of gamma-ray photons by the first and second detectors, with the sample being placed between the first and second detectors and the sample being placed between the first or second detector and the sample. In the first measurement mode, the processing unit determines the location where the gamma-ray photon was Compton-scattered within the subject by the gamma-ray photon, based on the detection position and time of the gamma-ray photon by the first and second detectors respectively, and the position of the positron-emitting nuclide, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in a positron-emitting nuclide, by considering that the gamma-ray photon arriving at one of the first and second detectors arrived without Compton scattering within the subject, and that the gamma-ray photon arriving at the other detector arrived after Compton scattering within the subject, and then creates a first tomographic image representing the distribution of Compton scattering locations within the subject obtained for each of the multiple simultaneous counting events. Image acquisition device.

2. In the second measurement mode, the measurement unit outputs signals representing the detection position and time of gamma-ray photons by the first and second detectors, with the subject, who has been administered a drug labeled with a positron-emitting nuclide, placed between the first and second detectors. The aforementioned processing unit, In the second measurement mode, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in a positron-emitting nuclide, the location where the annihilation event occurred is determined based on the detection position and detection time of the gamma-ray photons by the first and second detectors, respectively, using the difference in detection times between the first and second detectors. A second tomographic image is then created representing the distribution of the annihilation event locations in the subject, obtained for each of the multiple simultaneous counting events. The second tomographic image is corrected based on the first tomographic image. The image acquisition device according to claim 1.

3. A measuring unit includes a first detector and a second detector, each detecting gamma-ray photons, and outputs signals representing the detection position and detection time when the first detector and the second detector each detect a gamma-ray photon. A processing unit that processes the signals output from the first detector and the second detector, respectively, Equipped with, The measurement unit outputs signals representing the detection position and time of gamma-ray photons by the first and second detectors, respectively, when a subject who has been administered a drug labeled with a positron-emitting radionuclide is placed between the first and second detectors, and when the positron-emitting radionuclide is placed between the first or second detector and the subject. The aforementioned processing unit, For each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in a positron-emitting nuclide, If a gamma-ray photon arriving at one of the first and second detectors arrives within the subject without Compton scattering, and a gamma-ray photon arriving at the other detector arrives within the subject after Compton scattering, the position where the gamma-ray photon was Compton-scattered within the subject is determined using the difference in detection times between the first and second detectors, based on the detection position and detection time of the gamma-ray photon by the first and second detectors, respectively, and the position of the positron-emitting nuclide placed between the first or second detector and the subject. If the gamma-ray photons arriving at both the first and second detectors arrive within the subject without Compton scattering, the location where the annihilation event occurred is determined using the difference in detection times between the first and second detectors, based on the detection positions and detection times of the gamma-ray photons by the first and second detectors, respectively. A first tomographic image is created representing the distribution of Compton scattering locations in the subject obtained for each of multiple simultaneous counting events, a second tomographic image is created representing the distribution of annihilation event locations in the subject obtained for each of multiple simultaneous counting events, and the second tomographic image is corrected based on the first tomographic image. Image acquisition device.

4. The positron-emitting radionuclide placed between the first detector or the second detector and the subject, and the positron-emitting radionuclide used to label the drug administered to the subject, are of the same type. The image acquisition device according to claim 2 or 3.

5. The processing unit determines whether or not a gamma-ray photon arriving at the first detector or the second detector has undergone Compton scattering, based on one or more of the following: the position of the positron-emitting nuclide, the magnitude of the gamma-ray photon's energy, and the detection time of the gamma-ray photon by the first detector and the second detector, respectively. An image acquisition device according to any one of claims 1 to 3.

6. The measurement unit outputs signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector, respectively, with a positron-emitting nuclide placed between the first detector and the subject, and also between the second detector and the subject. An image acquisition device according to any one of claims 1 to 3.

7. The measurement unit outputs signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector, respectively, with the detection surface of the first detector being narrower than that of the second detector, and with a positron-emitting nuclide placed between the first detector and the subject. An image acquisition device according to any one of claims 1 to 3.

8. The measuring unit further includes a shielding body that prevents gamma-ray photons backscattered from either the first detector or the second detector from entering the other. An image acquisition device according to any one of claims 1 to 3.

9. The measurement unit further includes a moving unit for moving a positron-emitting nuclide between the first detector or the second detector and the sample. An image acquisition device according to any one of claims 1 to 3.

10. A measurement step in which a first detector and a second detector, each detecting gamma-ray photons, are used, and when the first detector and the second detector each detect a gamma-ray photon, signals representing the detection position and detection time are output, A processing step for processing the signals output from the first detector and the second detector, respectively, Equipped with, In the first measurement mode, the measurement step involves placing the subject between the first detector and the second detector, and placing a positron-emitting nuclide between the first detector or the second detector and the subject, and outputting signals representing the detection position and time of gamma-ray photons by the first detector and the second detector, respectively. In the first measurement mode, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in a positron-emitting nuclide, the gamma-ray photon arriving at one of the first and second detectors is assumed to have arrived in the subject without Compton scattering, and the gamma-ray photon arriving at the other detector is assumed to have arrived after Compton scattering in the subject. Based on the detection position and detection time of the gamma-ray photon by the first and second detectors, respectively, and the position of the positron-emitting nuclide, the position where the gamma-ray photon was Compton-scattered in the subject is determined using the difference in detection times between the first and second detectors, and a first tomographic image is created representing the distribution of Compton scattering positions in the subject obtained for each of the multiple simultaneous counting events. How to acquire images.

11. In the second measurement mode, the measurement step involves the subject, who has been administered a drug labeled with a positron-emitting radionuclide, being placed between the first detector and the second detector, and outputting signals representing the detection position and time of gamma-ray photons by the first detector and the second detector, respectively. The processing step described above is: In the second measurement mode, for each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons generated by an electron-positron annihilation event in a positron-emitting nuclide, the location where the annihilation event occurred is determined based on the detection position and detection time of the gamma-ray photons by the first and second detectors, respectively, using the difference in detection times between the first and second detectors. A second tomographic image is then created representing the distribution of the annihilation event locations in the subject, obtained for each of the multiple simultaneous counting events. The second tomographic image is corrected based on the first tomographic image. The image acquisition method according to claim 10.

12. A measurement step in which a first detector and a second detector, each detecting gamma-ray photons, are used, and when the first detector and the second detector each detect a gamma-ray photon, signals representing the detection position and detection time are output, A processing step for processing the signals output from the first detector and the second detector, respectively, Equipped with, The measurement step involves placing a subject who has been administered a drug labeled with a positron-emitting radionuclide between the first detector and the second detector, and with the positron-emitting radionuclide placed between the first detector or the second detector and the subject, and outputting signals representing the detection position and time of gamma-ray photons by the first detector and the second detector, respectively. The processing step described above is: For each simultaneous counting event in which the first and second detectors simultaneously count a pair of gamma-ray photons produced by an electron-positron annihilation event in a positron-emitting nuclide, If a gamma-ray photon arriving at one of the first and second detectors arrives within the subject without Compton scattering, and a gamma-ray photon arriving at the other detector arrives within the subject after Compton scattering, the position where the gamma-ray photon was Compton-scattered within the subject is determined using the difference in detection times between the first and second detectors, based on the detection position and detection time of the gamma-ray photon by the first and second detectors, respectively, and the position of the positron-emitting nuclide placed between the first or second detector and the subject. If the gamma-ray photons arriving at both the first and second detectors arrive within the subject without Compton scattering, the location where the annihilation event occurred is determined using the difference in detection times between the first and second detectors, based on the detection positions and detection times of the gamma-ray photons by the first and second detectors, respectively. A first tomographic image is created representing the distribution of Compton scattering locations in the subject obtained for each of multiple simultaneous counting events, a second tomographic image is created representing the distribution of annihilation event locations in the subject obtained for each of multiple simultaneous counting events, and the second tomographic image is corrected based on the first tomographic image. How to acquire images.

13. The positron-emitting radionuclide placed between the first detector or the second detector and the subject, and the positron-emitting radionuclide used to label the drug administered to the subject, are of the same type. The image acquisition method according to claim 11 or 12.

14. The processing step determines whether or not a gamma-ray photon arriving at the first detector or the second detector has undergone Compton scattering, based on one or more of the following: the position of the positron-emitting nuclide, the magnitude of the energy of the gamma-ray photon, and the detection time of the gamma-ray photon by the first detector and the second detector, respectively. The image acquisition method according to any one of claims 10 to 12.

15. The measurement step involves placing a positron-emitting nuclide between the first detector and the subject, and also placing a positron-emitting nuclide between the second detector and the subject, and outputting signals representing the detection position and detection time of gamma-ray photons by the first detector and the second detector, respectively. The image acquisition method according to any one of claims 10 to 12.

16. The measurement step involves using a first detector with a narrower detection surface than the second detector, placing a positron-emitting nuclide between the first detector and the subject, and outputting signals representing the detection position and time of gamma-ray photons by the first detector and the second detector, respectively. The image acquisition method according to any one of claims 10 to 12.

17. The measurement step involves using a shield to prevent gamma-ray photons backscattered from either the first detector or the second detector from entering the other. The image acquisition method according to any one of claims 10 to 12.

18. The measurement step involves moving a positron-emitting nuclide between the first detector or the second detector and the sample. The image acquisition method according to any one of claims 10 to 12.

Images