JP2007071858A - Method, program, and storage medium for radiation coincidence counting, as well as, radiation coincidence counter and nuclear medicine diagnosis apparatus using same, storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for radiation coincidence counting, and to provide a program and storage medium for radiation coincidence counting, as well as a radiation coincidence counter and nuclear medicine diagnosis apparatus using the same, storage medium. <P>SOLUTION: In this method, coincidence counting of radiation generated from analyte with dosed radiopharmaceutical is made (Step T1). With reference to at Table for coincidence counting patterns created in Step S1-S4, output information of coincidence counted radiation is divided into information on true coincidence counting and information on accidental or scattering coincidence counting (Step T2). Consequently, coincidence counting of radiation can be made more accurately. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radiation coincidence processing method, a radiation coincidence processing program and a radiation coincidence processing storage medium for simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, a radiation coincidence processing apparatus, and a radiation coincidence apparatus and the same. In particular, the present invention relates to a technique for simultaneously counting radiation.

  As the above-described nuclear medicine diagnosis apparatus, that is, an ECT (Emission Computed Tomography) apparatus, a PET (Positron Emission Tomography) apparatus will be described as an example. The PET apparatus detects a plurality of γ-rays generated by annihilation of protons, that is, positrons, and reconstructs a tomographic image of a subject only when γ-rays are detected simultaneously by a plurality of detectors. It is configured.

  In this PET apparatus, after a radiopharmaceutical is administered to a subject, the process of drug accumulation in the target tissue is measured over time, whereby quantitative measurement of various biological functions is possible. Therefore, the tomographic image obtained by the PET apparatus has functional information.

  By the way, in the technique of simultaneously detecting γ rays, that is, simultaneously counting γ rays, in addition to 2D-PET that detects γ rays two-dimensionally, in recent years, 3D-PET that detects γ rays three-dimensionally is used. It is used. In such 3D-PET, by arranging each detector in the vicinity of the subject at a large solid angle, the detection efficiency of γ rays can be increased, and the sensitivity of the detector can be dramatically improved.

In order to simultaneously count γ-rays, each γ-ray is input to the coincidence counting circuit, and it is determined whether or not the time difference between the input γ-rays is within a predetermined time window. In an actual coincidence circuit, γ rays detected within a very short time window of 10 ns to 20 ns (ns = 10 ⁻⁹ s) are regarded as “simultaneous”. Therefore, there is a possibility that one of γ rays generated at two different points is counted simultaneously. This is called “random coincidence”. FIG. 6A is a schematic diagram schematically showing the state of the coincidence coincidence. On the other hand, when one or both of the pair of γ-rays are simultaneously counted after causing Compton scattering in the subject, this is called “scatter coincidence”. A schematic diagram schematically showing the state of the scattering coincidence is shown in FIG. The hatched portion in the detector in FIG. 6 indicates the coincidence detector. In addition, when both of a pair of γ rays are counted simultaneously, this is called “true coincidence”.

  However, as the number of coincidence detector sets increases, the noise components such as random or scattered coincidence described above also increase. When the noise component increases, the S / N ratio of the obtained image tends to reach a peak. This will be described with reference to FIG. FIG. 7 is a graph schematically showing a count rate characteristic indicating a change in the coincidence count rate with respect to the concentration of the radiopharmaceutical administered to the subject. True coincidence is proportional to the concentration of radiopharmaceutical (“radioactivity concentration” in FIG. 7), while incidental coincidence is proportional to the square of that concentration. Therefore, the true coincidence rate reaches its peak. The S / N ratio of the image reaches its peak for the same reason as the coincidence rate. For this reason, a good S / N ratio cannot be obtained except for the peak S / N ratio due to incidental noise and noise of coincidence of scattering.

  Therefore, there is a need for a technique for reducing noise components such as accidents and scattered coincidence while improving the sensitivity of true coincidence. The following are examples of conventional techniques for reducing these noise components.

  The accidental coincidence count can be reduced by narrowing the time window described above. Further, the scattering coincidence count can be reduced by narrowing the energy window (see, for example, Non-Patent Document 1).

  A TOF (Time of Flight) type PET that improves the S / N ratio of an image by specifying the source of γ rays (proton disappearance position) using the difference in detection time of each γ ray has been proposed ( For example, refer nonpatent literature 2).

In addition, as shown in FIG. 8, a Compton camera that calculates the incident direction of γ rays from the energy of a detector in which scintillators are stacked in multiple layers has been studied using Compton scattering of the detector (for example, non-patent) Reference 3).
Akihisa Fujibayashi Masatoshi Taguchi, Masaharu Amano, “Nuclear Medicine Imaging System”, first edition, Corona Inc., April 25, 2002, p. 121-122 WW Moses, "Time of Flight in PET Revisited", IEEE Trans. Nucl. Sci., Vol. 50, pp. 1325-1330, 2003. JE Gillam, TE Beveridge, "Positron Emission Imaging Using Acquired Cone-Surfaces from Opposing Compton Cameras", Conf. Rec. NSS & MIC, M3-4

  However, in the case of Non-Patent Document 1 described above, the time resolution such as the time window and the energy resolution such as the energy window are determined by the scintillator crystal constituting the detector. Therefore, there is a limit to the significant improvement in performance, and these windows cannot be sufficiently narrowed.

  Further, in the case of Non-Patent Document 2 described above, there is no scintillator crystal that can detect a difference in detection time at the present stage. That is, since there is no high-speed and high-sensitivity scintillator crystal, it has not been put into practical use. In addition, the effect of TOF is limited to a large body person when the subject is a human body, and it is difficult to apply it to clinical and small animals for a small body person such as Japanese.

  In the case of Non-Patent Document 3 described above, Compton scattering is assumed to occur. If γ rays pass through the scintillator crystal or stay in the scintillator crystal, they cannot be used. Furthermore, it is difficult to develop a detector that achieves both sensitivity and energy resolution, and there is a limit to the accuracy of estimation of the incident direction. Therefore, it is difficult to obtain an image with high resolution and high sensitivity with only one γ ray (single γ ray).

  The present invention has been made in view of such circumstances, and a radiation coincidence processing method, a radiation coincidence processing program, a radiation coincidence processing storage medium, and a radiation coincidence counting processing storage medium capable of performing simultaneous coincidence of radiation with higher accuracy, and An object is to provide a radiation coincidence apparatus, a nuclear medicine diagnosis apparatus using the same, and a storage medium.

In order to achieve such an object, the present invention has the following configuration.
That is, the invention according to claim 1 is a radiation coincidence processing method for performing a series of radiation coincidence processing including a coincidence counting step of simultaneously counting radiation generated from a subject administered with a radiopharmaceutical, (A) A simultaneous counting step for simultaneously counting radiation generated from the subject, and (B) output information for each incident angle obtained by detecting radiation by entering the radiation detector to be simultaneously detected. Based on this, the output information when simultaneously detected at a predetermined incident angle is information relating to true coincidence, and the output information when being simultaneously detected at other incident angles is assumed to be information relating to coincidence or scattered coincidence counting. And a counting / separating step for separating the components.

  [Operation / Effect] According to the first aspect of the invention, in the coincidence step (A), the radiation generated from the subject to which the radiopharmaceutical is administered is simultaneously counted. In the counting / separating step (B), detection is performed simultaneously at a predetermined incident angle based on output information for each incident angle obtained by making radiation incident on the radiation detector to be simultaneously detected. The output information at this time is used as information regarding true coincidence counting, and the output information when simultaneously detected at other incident angles is separated as information regarding coincidence or scattering coincidence counting. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, the simultaneous counting of radiation can be performed with higher accuracy.

  The invention according to claim 2 is a radiation coincidence counting process for causing a computer to execute a series of radiation coincidence processes including a coincidence counting step of simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered. (A) a coincidence counting step for simultaneously counting radiation generated from the subject; and (B) an incident angle obtained by detecting radiation incident on a radiation detector to be simultaneously detected. Based on the output information of each, the output information when simultaneously detected at a predetermined incident angle is the information regarding the true coincidence, and the output information when simultaneously detected at other incident angles is the coincidence or scattering coincidence The computer is configured to cause a computer to execute a radiation simultaneous counting process including a counting / separating step of separating the information so as to be information.

  [Operation / Effect] According to the invention described in claim 2, in the coincidence counting step (A), the radiation generated from the subject to which the radiopharmaceutical is administered is simultaneously counted. In the counting / separating step (B), detection is performed simultaneously at a predetermined incident angle based on output information for each incident angle obtained by making radiation incident on the radiation detector to be simultaneously detected. The output information at this time is used as information regarding true coincidence counting, and the output information when simultaneously detected at other incident angles is separated as information regarding coincidence or scattering coincidence counting. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, it is possible to perform the simultaneous counting of radiation with higher accuracy by causing the computer to execute a radiation simultaneous counting process including these steps.

  The invention according to claim 3 is a radiation coincidence counting process for causing a computer to execute a series of radiation coincidence processes including a coincidence counting step of simultaneously counting radiation generated from a subject administered with a radiopharmaceutical. A computer readable radiation coincidence processing storage medium storing a program, wherein (A) a coincidence counting step for simultaneously counting radiation generated from the subject, and (B) radiation detection to be subjected to simultaneous detection Based on the output information for each incident angle obtained by detecting radiation incident on the vessel, the output information when simultaneously detected at a predetermined incident angle is used as information regarding true coincidence, and other incident angles A radiation coincidence process including a separation step for separating the output information at the same time as the information relating to coincidence or scattering coincidence information. It is characterized in storing a program to be executed by the computer.

  [Operation / Effect] According to the invention described in claim 3, in the counting and separating step of (B), for each incident angle obtained by detecting the radiation incident on the radiation detector to be simultaneously detected. Based on the output information, the output information when simultaneously detected at a predetermined incident angle is information related to true coincidence, and the output information when simultaneously detected at other incident angles is information related to incidental or scattered coincidence information. And so on. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, it is possible to perform the simultaneous counting of radiation with higher accuracy by causing the computer to execute a radiation simultaneous counting process including these steps.

  The invention according to claim 4 is a radiation coincidence counting device that simultaneously counts radiation generated from a subject administered with a radiopharmaceutical, (α) a radiation detector that detects incident radiation; (Β) output information storage means for storing output information for each incident angle obtained by detecting radiation incident on a radiation detector to be simultaneously detected; and (γ) output from the output information storage means. Based on the information, the output information when simultaneously detected at a predetermined incident angle is information regarding true coincidence, and the output information when simultaneously detected at other incident angles is information regarding accidental or scattered coincidence counting and And a calculation means for performing calculation processing to be separated.

  [Operation / Effect] According to the invention described in claim 4, the radiation generated from the subject to which the radiopharmaceutical is administered is detected by the radiation detector (α) to obtain output information. (Β) output information storage means stores output information for each incident angle obtained by making radiation incident on a radiation detector to be simultaneously detected, and (γ) calculation means. Based on the output information from the output information storage means, the output information when simultaneously detected at a predetermined incident angle is information on the true coincidence, and the output information when simultaneously detected at other incident angles A calculation process is performed so that the information is related to incidental or scattered coincidence counting. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, the simultaneous counting of radiation can be performed with higher accuracy.

  The invention according to claim 5 is a nuclear medicine diagnostic apparatus using a radiation coincidence counting device that simultaneously counts radiation generated from a subject to which a radiopharmaceutical has been administered, wherein (α) incident radiation is A radiation detector to detect, (β) output information storage means for storing output information for each incident angle obtained by making radiation incident on a radiation detector to be simultaneously detected, and (γ) said Based on the output information from the output information storage means, the output information when it is simultaneously detected at a predetermined incident angle is information on the true coincidence, and the output information when it is simultaneously detected at other incident angles is accidental. Alternatively, a calculation unit that performs a calculation process to separate the information so as to be information related to the scattering coincidence count, and (δ) an image processing unit that performs image processing based on the information related to the true simultaneous count separated by the calculation process It includes, and is characterized in carrying out the nuclear medicine diagnosis based on the images obtained by the image processing means.

  [Operation / Effect] According to the invention described in claim 5, output information when (γ) is simultaneously detected at a predetermined incident angle on the basis of output information from the output information storage means based on the output information from the output information storage means. Information processing regarding true coincidence is performed, and output processing when output is detected simultaneously at other incident angles is separated so as to be information relating to coincidence or scattering coincidence. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, the simultaneous counting of radiation can be performed with higher accuracy. Further, by performing the simultaneous counting of the radiation with higher accuracy, the nuclear medicine diagnosis can be performed more accurately based on the image obtained by the image processing means (δ).

  The invention according to claim 6 is the output information for each incident angle obtained by detecting the radiation incident on the radiation detector to be simultaneously detected according to claims 1 to 5. , Is characterized by a storage medium.

  [Operation / Effect] According to the invention described in claim 6, the storage medium stores the output information for each incident angle obtained by detecting the radiation incident on the radiation detector to be simultaneously detected. ing.

  According to the radiation coincidence processing method, the radiation coincidence processing program and the radiation coincidence processing storage medium, and the radiation coincidence apparatus, the nuclear medicine diagnosis apparatus using the same, and the storage medium according to the present invention, they are objects of simultaneous detection. Based on the output information for each incident angle obtained by detecting the radiation incident on the radiation detector, the output information when simultaneously detected at a predetermined incident angle is set as information on the true coincidence, and other than that The output information when simultaneously detected at the incident angle is separated into information related to incidental or scattered coincidence counting. By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, the simultaneous counting of radiation can be performed with higher accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view and a block diagram of a PET (Positron Emission Tomography) apparatus according to an embodiment. In this embodiment, a PET apparatus will be described as an example of a nuclear medicine diagnosis apparatus.

  As shown in FIG. 1, the PET apparatus according to the present embodiment includes a top plate 1 on which a subject M is placed. The top plate 1 is configured to move up and down and translate along the body axis Z of the subject M. With this configuration, the subject M placed on the top 1 is scanned from the head to the abdomen and foot sequentially through the opening 2a of the gantry 2, which will be described later. Diagnostic data such as projection data and tomographic images are obtained.

  In addition to the top plate 1, the apparatus according to the present embodiment includes a gantry 2 having an opening 2a, a plurality of scintillator blocks 3a and a plurality of photomultipliers 3b arranged close to each other. In this embodiment, as shown in FIG. 4, a scintillator block 3a composed of a 16 × 16 scintillator and a photomultiplier 3b composed of 16 × 16 detection elements are used, but the number of detection elements of the photomultiplier 3b is more than the number of scintillators. May be less. The scintillator block 3 a and the photomultiplier 3 b are arranged in a ring shape so as to surround the body axis Z of the subject M, and are embedded in the gantry 2. The photomultiplier 3b is disposed outside the scintillator block 3a.

  As a specific arrangement of the γ-ray detector 3 composed of the scintillator block 3a and the photomultiplier 3b, for example, 16 scintillators of the γ-ray detector 3 are arranged in a direction parallel to the body axis Z of the subject M. When the γ-ray detector 3 surrounding the subject M is formed of a multi- (L) square ring, L γ-ray detectors 3 are arranged on each side of the polygon, that is, the L unit detector is the body of the subject M. The form arrange | positioned so that the circumference | surroundings of the axis | shaft Z may be mentioned is mentioned. The number of γ-ray detectors 3 arranged according to the diameter of the γ-ray detector 3 surrounding the subject M is not limited to L. The combination of a pair of γ-ray detectors 3 that simultaneously detect γ-rays, that is, simultaneously count γ-rays, is in the two γ-ray detectors 3 units facing each other across the subject M lying in the center of the ring. One pair of γ-ray detectors constitutes a pair. Further, in this embodiment, the scintillator block 3a is configured such that Compton scattering is likely to occur by stacking scintillator layers in multiple layers. The γ-ray detector 3 is a three-dimensional (DOI) detector. The γ-ray detector 3 including the scintillator block 3a and the photomultiplier 3b corresponds to the radiation detector in the present invention.

  In addition, the apparatus of the present embodiment includes a top plate driving unit 4, a controller 5, a memory unit 6, an input unit 7, an output unit 8, a coincidence circuit 9, and a reconstruction unit 10. The top plate drive unit 4 is a mechanism for driving the top plate 1 so as to perform the above-described movement, and includes a motor or the like not shown.

  The controller 5 comprehensively controls each part constituting the apparatus of this embodiment. The controller 5 includes a central processing unit (CPU). In this embodiment, the controller 5 has a function of referring to a later-described coincidence pattern pattern table 6a of the memory unit 6 and executing a calculation process related to the γ-ray coincidence process shown in FIG. Further, when the γ-ray coincidence processing is executed, it is performed by reading a later-described γ-ray coincidence processing program 6 b in the memory unit 6. Therefore, the controller 5 corresponds to the computing means in this invention.

  The memory unit 6 is composed of a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. In the present embodiment, the data processed by the coincidence counting circuit 9 and the reconstruction unit 10 is written and stored in the RAM, and is read from the RAM as necessary. The ROM stores in advance a coincidence pattern table 6a and a γ ray coincidence processing program 6b. A specific method for creating the coincidence pattern table 6a and a specific process of the γ-ray coincidence processing program 6b will be described later with reference to the flowchart of FIG. 2, and the contents of the coincidence pattern table 6a are illustrated in FIG. This will be described later with reference to FIG. The coincidence pattern table 6a corresponds to output information storage means (storage medium) in the present invention, and the ROM storing the γ-ray coincidence processing program 6b corresponds to the radiation coincidence processing storage medium in the present invention.

  The input unit 7 sends data and commands input by the operator to the controller 5. The input unit 7 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. The output unit 8 includes a display unit represented by a monitor, a printer, and the like.

  The reconfiguration unit 10 is realized by the controller 5 executing a program stored in the ROM of the memory unit 6 or an instruction input from the input unit 7. The reconstruction unit 10 together with the memory unit 6 corresponds to the image processing means in the present invention.

  The scintillator block 3a converts γ rays generated from the subject M to which a radiopharmaceutical, that is, a radioisotope (RI) is administered, into light, and the photomultiplier 3b photoelectrically converts the converted light into an electrical signal. Output to. The electric signal is sent to the coincidence circuit 9 as image information (pixel).

  Specifically, when a radiopharmaceutical is administered to the subject M, two γ rays are generated due to the disappearance of the positron of the positron emission type RI. The coincidence counting circuit 9 checks the position of the emitted scintillator block 3a and the incident timing of the γ rays, and only sends the image information sent when the γ rays are incident on the two scintillator blocks 3a constituting the pair at the same time. Judged as appropriate data. When γ rays are incident on only one of the two scintillator blocks 3a constituting the pair, the coincidence counting circuit 9 treats them as noise instead of γ rays generated by annihilation of positrons, and the image information sent at that time Judge it as noise and reject it.

  Actually, even if the coincidence counting circuit 9 performs such processing, the noise cannot be completely removed, and noise components such as accidental or scattered coincidence remain. Therefore, subsequently, the γ-ray coincidence processing described above is performed to separate the image information corresponding to the output information into information relating to true coincidence and information relating to coincidence or scattered coincidence counting.

  The image information sent to the coincidence circuit 9 is sent to the reconstruction unit 10 as projection data. The reconstruction unit 10 reconstructs the projection data to obtain a tomographic image of the subject M. The tomographic image is sent to the output unit 8 via the controller 5. In this way, nuclear medicine diagnosis is performed based on the tomographic image obtained by the reconstruction unit 10.

  A specific method for creating the coincidence pattern table 6a and a specific process of the γ-ray coincidence processing program 6b will be described with reference to the flowchart of FIG. This will be described with reference to the explanatory diagrams of FIGS. FIG. 2 is a flowchart showing the flow of a series of a process for creating the coincidence pattern table 6a prepared in advance and a coincidence process by the γ-ray coincidence process program 6b when an unknown γ-ray is detected. It is. FIG. 3 is an explanatory diagram schematically showing an event when the incident angle is changed, and FIG. 4 is an explanatory diagram schematically showing an example of an output distribution from the photomultiplier 3b. Yes, (a) is when the photoelectric effect due to normal emission of γ rays occurs in the crystal of the scintillator block 3a, and (b) is when Compton scattering occurs. FIG. 3 shows an example of a configuration in which two γ-ray detectors that form a pair and perform simultaneous measurement are arranged opposite to each other on an axis that passes through the central axis of the ring and is perpendicular to the central axis. I will explain. In this case, the opposing axis is said to be perpendicular to the center axis of the ring.

  In this specification, “event” means that the number of events is changed to N (the number of events) by repeating the operation of detecting γ-rays incident on the γ-ray detector 3 to be simultaneously detected while changing the incident angle. In the embodiment, 2000). In addition, “dimension” in the present specification is the total number of channels of two γ-ray detectors 3 that form a pair and perform simultaneous counting.

(Step S1) Simulation for Each Event As shown in FIG. 3, two γ-ray detectors 31 constituting a pair to be simultaneously detected are prepared for the simulation, and the γ-ray detector 31 is provided with γ-rays. The number of events is increased by repeating the operation of detecting the incident by changing the incident angle.

  As for the γ-rays incident on the γ-ray detector 31, γ-rays to be simultaneously detected are used without using γ-rays generated from the subject M to which the radiopharmaceutical is administered. That is, a gamma ray source (not shown) is provided, and gamma rays irradiated from the gamma ray source are used. At this time, a collimator (not shown) made of lead (Pb) or the like is provided to adjust the incident angle of γ rays so that the incident angle can be set to a desired angle. In FIG. 3, γ-rays are incident on the two detectors that perform the paired simultaneous measurement at incident angles θ of 0 °, 15 °, 30 °, and 45 ° (when N = 4), The subsequent processing is shown. Note that the scattering pattern as shown in FIG. 4 caused by the incidence of gamma rays is different for each detector even when γ rays are incident on the opposite γ-ray detector 3 at the same angle.

(Step S2) Pattern Separation In the pair configuration of FIG. 3, when incident angle θ is 0 ° and γ-rays are incident on both of the pair of detectors at the same time, the γ-rays are incident without scattering or accidental occurrence. The image information obtained at that time is used as information regarding true coincidence. On the other hand, when the incident angle θ is 15 °, 30 °, or 45 ° other than that, it is assumed that γ rays are incident by Compton scattering or incidentally, and the image information obtained at that time is incidentally or Information related to the scattering coincidence count. In this way, the information on the true coincidence and the information on the coincidence or scattering coincidence are divided into patterns according to the incident angles to obtain the coincidence pattern.

  As described above, the combination of the pair of γ-ray detectors 3 to be simultaneously detected is not only the combination in which the opposing axes are perpendicular to the center axis of the ring as shown in FIG. Also included are combinations that do not pass through the central axis of the ring. These are also divided into patterns in the same procedure as the method described in FIG. In this case, the incident angle regarded as information related to true coincidence is α °, and other incident angles are regarded as information relating to coincidence or scattered coincidence counting (see FIG. 11B). That is, a combination of γ-ray detectors capable of simultaneous counting is selected in advance in consideration of the positional relationship between the γ-ray detector unit and the subject M facing each other. All patterns are divided and classified into information on true coincidence and information on incidental or scattered coincidence.

  In a pair in which the opposing axes of the γ-ray detectors are perpendicular to the center axis of the ring, θ = 0 °. When the opposing axis does not pass through the central axis, as shown in FIG. The angle formed by the line connecting the two and the detection center axis of each detector (the vertical axis set up from the center of the detection surface of the detector) is a predetermined angle in the claims.

Then, in the pair in which the opposing axes do not pass through the center axis of the ring, since the positional relationship between the pair of γ-ray detectors capable of simultaneous counting and the positional relationship with the subject M is known as described above, the true simultaneous counting is performed. The incident angle α ° regarded as the information on the relationship can be obtained based on the positional relationship. As shown in FIG. 11 (a), for example, the distance of the detectors and t _1, the distance of the detection center axis of the respective detector (vertical axis standing from the center of the detection surface of the detector) When t ₂ , Α ° (= α ′ [rad]) = sin− ¹ (t ₂ / t ₁ ), a predetermined angle α ° can be obtained.

  An example of the output distribution from the photomultiplier 3b constituting the γ-ray detector 31 to be simultaneously detected is as shown in FIG. The output distribution of FIG. 4 is a distribution of image information by the γ-ray detector 3 for 16 channels × 16 channels vertically and horizontally (“16ch” in FIG. 4). If a photoelectric effect occurs in the crystal of the scintillator block 3a as shown in FIG. 4 (a), it stays in the crystal and is absorbed, but it is related to the true coincidence without judging accidental or scattering. Used as an event ("photoelectric absorption event" in FIG. 3). If Compton scattering occurs in the crystal of the scintillator block 3a as shown in FIG. 4B, the light shines white at at least two points. These events, including photoelectric absorption events, are used as multiple scattering events.

(Step S3) Has the number of events been reached?
Steps S1 and S2 described above are performed for each event, and it is determined whether or not the number of events N (the present embodiment 2000) has been reached. If the number of events N has not been reached, the process returns to step S1 and steps S1 and S2 are repeated. If the number of events N has been reached, the process proceeds to the next step S4.

(Step S4) Storage in the coincidence pattern table The number of coincidence patterns divided in this way for the pair of γ-ray detectors is a product of the number of dimensions and the number of events. FIG. 3 illustrates the case where 512 dimensions × N (2000) coincidence patterns are obtained. The matrix in FIG. 3 includes N rows and 512-dimensional columns, “Anode” indicates image information, and the first subscript of “Anode” is the number of events [1, 2,. ]. In the matrix in FIG. 3, among the last subscripts of “Anode”, “det1” indicates one γ-ray detector 31, and “det2” faces one γ-ray detector 31. The other gamma ray detector is shown.

  Various coincidence patterns as shown in FIG. 3 are stored in the coincidence pattern table 6a for each pair of γ-ray detectors to be simultaneously detected. Such a coincidence pattern is used for referring to a coincidence pattern table (also referred to as “pattern matching”) described later (step T2). For example, a pattern recognition method using a support vector machine (SVM) may be used to create the coincidence pattern table (Maeda Eisaku, Exciting! Support vector machine-old and new pattern recognition method, “Information processing” "NTT Communication Science Laboratories, Vol. 42, No. 7, July 2001".

  A more specific description will be given with reference to FIG. FIG. 9 is an explanatory view schematically showing a state when patterning image information in a certain combination of γ-ray detectors to be simultaneously detected. FIG. 9 shows a state when the number of events is small. FIG. 9B shows a state when the number of events is further increased. For convenience of explanation, FIG. 9 and FIG. 10 to be described later schematically show image information of a plurality of dimensions (512 dimensions in FIG. 3), which is the total number of channels of a pair of γ-ray detectors 3 that perform coincidence counting, in a planar shape. Suppose that it is a figure shown.

  Including step S4, the process of step S described above will be applied to SVM. In SVM, what can be handled quantitatively, such as the dimensions of the γ-ray detector described above, is called a “feature”. If attention is paid to such d feature quantities, the image information detected by a certain γ-ray detector can be represented as one point x in a d-dimensional space called “feature space”. This d-dimensional vector x is called a “pattern” or “feature vector”, and in particular, a pattern obtained from image information detected by a γ-ray detector is called a “learning pattern”. As shown in FIG. 3, in the case of 512 dimensions, 512 feature amounts, that is, d-dimensional feature vectors x are 512. In addition, for each combination of a pair of γ-ray detectors (targets of simultaneous detection), 512-dimensional vector image information is obtained by the number of events N over the above-described steps S1 to S3. Such operations in steps S1 to S3 are referred to as “learning”, and image information obtained by learning is referred to as “identification rule”.

In step S2, information about true coincidence and information about coincidence or scatter coincidence are classified into χ _1, and a set of information concerning true coincidence is χ ₁ and a set of information concerning coincidence or scatter coincidence is χ ₂ . To do. When the information regarding the true coincidence is “1” and the information regarding the coincidence or scattering coincidence is “−1”, the identification rule is expressed as the following equation (1).

F _W (x) in the above equation (1) is a function having x as an argument, and is called “discriminant function”. w is a vector representing the parameter of the function f. The identification boundary on the feature space is given by g _W (x) = 0.

The set of information χ ₁ related to the true coincidence count is shown by “◯” in FIG. 9, and the set of information χ ₂ related to the coincidence or scattered coincidence count is shown by “x” in FIG. The identification boundary g _W (x) = 0 on the feature space is, for example, as shown in FIG.

  In the same manner, the number of events is increased as in step S3, and the coincidence count on the feature space shown in FIG. 9 is obtained. The coincidence pattern is stored in the coincidence pattern table 6a. This counting pattern corresponds to output information in the claims. The steps S1 to S4 so far are the process of creating the coincidence pattern table 6a, and the detection by the γ-ray detector 31 according to the processes so far is performed by simulation.

  According to the method of creating the coincidence pattern table 6a, in step S1, an event of detecting γ rays incident on the γ ray detector 31 to be detected simultaneously is detected for each detector in steps S1 to S3. At the same time, the process is repeated while changing the incident angle θ, and image information that is output information for each incident angle θ is acquired.

  In step S2, image information when simultaneously detected at a predetermined incident angle θ (when θ is 0 ° in the present embodiment) is used as information regarding true coincidence, and other incident angles θ ( In this embodiment, image information when θ is detected at 15 °, 30 °, or 45 °) is used as information on incidental or scattered coincidence counting, and patterns are divided to obtain coincidence patterns. Such coincidence pattern acquisition is performed for each combination for all combinations of γ-ray detectors capable of simultaneous counting. In step S4, the coincidence pattern is stored in the coincidence pattern table 6a for each combination.

  In summary, the coincidence pattern table 6a obtained in this way is an image for each incident angle θ obtained by detecting γ-rays incident on the γ-ray detector 31 to be simultaneously detected. Based on the information, the output information when simultaneously detected at a predetermined incident angle θ is information related to true coincidence, and the output information when detected at other incident angles θ is information related to incidental or scattered coincidence counting. As shown in the table, coincidence counting patterns divided by simulation are stored in advance.

  The γ-ray coincidence processing program 6b is now ready to execute the next steps T1 and T2. Specifically, steps T1 and T2 are realized by incorporating the γ-ray coincidence processing program 6b into the apparatus of the embodiment, and the controller 5 reading and executing the γ-ray coincidence processing program 6b.

(Step T1) Actual coincidence processing Actual coincidence processing is performed using γ rays generated from the subject M to which the radiopharmaceutical is administered. When this γ-ray enters the γ-ray detector 3 shown in FIG. 1, the γ-ray detector 3 detects the emitted light and outputs image information. Note that the controller 5 controls the coincidence circuit 9 so as to output only when γ rays are simultaneously counted, as described above, regardless of true coincidence, coincidence or scattering coincidence. Step T1 corresponds to the coincidence step (A) in the present invention.

(Step T2) Referencing the coincidence pattern table As in the case of outputting the image information stored in the coincidence pattern table 6b created in steps S1 to S4, the unknown γ-rays coincidentally counted in step T1. Output image information.

  Next, the newly output image information is based on the output information indicating which part is output, and the reference result (that is, the identification rule in SVM) of the image information stored in the coincidence pattern table 6b. Thus, the image information of the unknown γ-ray is separated into information on true coincidence and information on incidental or scattered coincidence. The same processing is performed for other γ-ray image information to separate the unknown γ-ray image information into information relating to true coincidence and information relating to coincidence or scattering coincidence. This reference to the coincidence pattern table is also called pattern matching. Step T2 corresponds to the counting and separating step (B) in the present invention.

The pattern matching will be described more specifically with reference to FIG. As shown in FIG. 10, the image information of this unknown γ-ray is classified into either information on true coincidence count or information on coincidence / scatter coincidence count. Image information due to incidence of unknown γ rays is represented by “Δ”. Whether the image information of unknown γ-rays belongs to the set χ ₁ of information regarding the true coincidence represented by “◯” with reference to the identification boundary g _W (x) = 0 shown in FIG. 9 and FIG. or accidental, or to determine whether or not belonging to the set χ ₂ of the information about the scattered coincidence was represented by "×". FIG. 10 illustrates a case where image information of an unknown γ-ray represented by “Δ” belongs to a set of information χ ₁ related to true coincidence represented by “◯”. In this case, the image information of unknown γ rays represented by “△” is classified into information χ ₁ regarding true coincidence and separated from information χ ₂ regarding coincidence or scattered coincidence represented by “×”. Is done.

  According to the apparatus of this embodiment having the γ-ray coincidence processing and the above-described configuration, in step T1, the γ-ray detector 3 detects γ-rays generated from the subject M to which the radiopharmaceutical is administered, and Image information that is output information is acquired only at the time of coincidence counting. Then, in step T2, the controller 5 refers to the coincidence pattern pattern table 6b and separates the coincidence counted γ-ray image information into information relating to true coincidence and information relating to incidental or scattered coincidence counting.

  Specifically, based on output information (image information in the present embodiment) for each input angle θ obtained by making γ-rays incident on the γ-ray detector 31 to be simultaneously detected and detected. The output information when simultaneously detected at the incident angle θ is regarded as information regarding the true coincidence, and the output information when simultaneously detected at the other incident angle θ is separated as information regarding the coincidence or scattering coincidence. .

  By separating the information on the coincidence or scattering coincidence from the information on the true coincidence, the noise component relating to the coincidence or scattering coincidence can be reduced. As a result, the gamma ray coincidence process including these steps T1 and T2 can be executed by the controller 5 so that the gamma ray coincidence can be more accurately performed.

  In the apparatus according to the present embodiment, the nuclear medicine diagnosis can be performed more accurately based on the tomographic image obtained by the reconstruction unit 10 by performing the coincidence counting of γ rays with higher accuracy.

  The data of the coincidence pattern stored in the coincidence pattern table 6a is already divided into patterns. This data is used as data used for learning (Training Data), and data of unknown γ-ray image information is used as data not used for learning (Non Training Data). FIG. 5 shows the result of inputting each data to the above-described support vector machine (SVM) and examining the true / random discrimination ability. 5A shows a case where γ rays are incident on a 1 mm × 1 mm region, and FIG. 5B shows a case where γ rays are incident on a 5.8 mm × 5.8 mm region (both incident regions are shown in FIG. 5). Then, “Irradiation Area”). The vertical axis represents the identification accuracy (“Answer Ratio” in FIG. 5). When the incident angle θ is 0 ° and 15 °, the incident angle θ is 0 ° when the incident angle θ is 0 ° and 30 °. It is the result of the identification accuracy regarding the data (Training Data) used for learning at 45 ° and the data (Non Training Data) not used for learning. A single crystal is used as a scintillator to be incident.

  As for the data obtained by the simulation, that is, the data used for learning (Training Data), it can be seen from the results of FIG. 5 that the discrimination accuracy is better than that of the data not used for learning (Non Training Data). Although the single crystal scintillator is shown in FIG. 5, it is confirmed that True / Random can be discriminated with a certain accuracy although the identification accuracy decreases as it enters the polycrystal.

  The S / N ratio of an image of diagnostic data such as projection data and tomographic image of the subject M obtained by the apparatus of this embodiment is generally described by a noise equivalent count. When the noise equivalent count is NECR, the noise equivalent count NECR is expressed by the following equation (2).

NECR = (a × T) ² / (a × T + b × R + c × S) (2)
Here, T represents a true coincidence, R represents a random coincidence, and S represents a scatter coincidence. a, b, and c are proportional counts, and usually a = b = c = 1.

  By narrowing the time window and the energy window, it is possible to reduce the noise components of random and scattered coincidence counts R and S to some extent. Further, according to the present invention, T, R, and S are discriminated by separating true coincidence T from random coincidence and scattered coincidence R and S, and a> b or a> c. The noise equivalent count NECR can be improved.

  The extent to which the ratio of a, b, and c can be improved depends on the discrimination performance, but if there is a possibility that a certain level of discrimination ability can be obtained, it should be applied regardless of the type of detector. The noise equivalent count NECR can be improved beyond the limits of time resolution and energy resolution. In the present invention, it has been confirmed that a certain level of discriminating ability can be obtained based on the result of FIG. 5, and therefore, by applying the present invention, the noise equivalent count NECR can be improved regardless of the type of detector.

  Further, if the random component and the coincidence counting as noise components can be reduced, the diagnostic ability can be improved by improving the image quality, and the exposure can be reduced and the diagnostic time can be shortened by substantially improving the sensitivity. Since the effect obtained by the present invention does not depend on the size of the subject unlike the TOF (Time of Flight) method in Non-Patent Document 2 described above, it can be applied to a nuclear medicine diagnostic apparatus for whole body, head, and small animals. Can be widely applied.

  Furthermore, it is also effective in reducing background events that have been a problem when measuring positron nuclides that generate γ-rays other than γ-rays generated by positron annihilation (annihilation γ-rays). It is also considered effective for radiopharmaceuticals using long-lived nuclides.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, the PET apparatus has been described as an example. However, the present invention is a nuclear medicine apparatus that performs a nuclear medicine diagnosis by simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered. If there is, it can be applied without being limited to the PET apparatus.

  (2) In the above-described embodiment, the γ-ray detector 3 composed of the scintillator block 3a and the photomultiplier 3b is a stationary type that detects γ-rays while still, but the scintillator block 3a and the photomultiplier The rotating type 3b may detect γ rays while rotating around the subject M.

  (3) The present invention can also be applied to an apparatus provided with an external radiation source in the vicinity of the subject in order to perform absorption correction. That is, a radiopharmaceutical to be administered to the subject M, that is, radiation of the same type as the radioisotope (RI) is irradiated from an external source, absorption correction data (transmission data) is obtained, and absorption is performed using this absorption correction data. It is also possible to separate information about true coincidence and information about incidental or scattered coincidence before correction.

  (4) The present invention can also be applied to an apparatus combining a nuclear medicine diagnosis apparatus and an X-ray CT apparatus, such as a PET-CT including a PET apparatus and an X-ray CT apparatus.

  (5) In the embodiment described above, the output information (image information in the embodiment) is the output value of the electrical signal obtained from the multi-channel γ-ray detector, but the output information is not limited to this. Physical quantities such as the sum of distributions reconstructed from these electrical signals (energy information) and the size of the spread can be used as output information. Further, the pattern dividing method is not limited to the pattern recognition method using a support vector machine (SVM).

  (6) In the above-described embodiment, the scintillator layer is a three-dimensional (DOI) detector in which multiple layers are stacked. However, the type of detector is not particularly limited.

1 is a side view and a block diagram of a PET (Positron Emission Tomography) apparatus according to an embodiment. It is the flowchart which showed the series of flows of the creation process of the coincidence pattern table, and the coincidence process by the gamma ray coincidence process program. It is explanatory drawing which showed typically the event when an incident angle was changed in the combination which an opposing axis | shaft makes perpendicular | vertical with respect to the center axis | shaft of a ring. It is explanatory drawing which showed typically an example of the output distribution from a photomultiplier, (a) is a Compton scattering when the photoelectric effect by the normal light emission of (gamma) ray occurs in the crystal | crystallization of a scintillator block. Is when it happened. (A), (b) is the result of examining the discrimination ability of True / Random. (A) is the schematic which showed the mode of the coincidence coincidence typically, (b) is the schematic which showed the mode of the scattering coincidence typically. It is the graph which showed typically the count rate characteristic which shows the change of the coincidence rate with respect to the density | concentration of the radiopharmaceutical administered to a subject. It is a schematic diagram when using the conventional Compton camera. (A), (b) is explanatory drawing which showed typically a mode when image information in a certain combination of the gamma ray detector used as the object of simultaneous detection is divided. It is explanatory drawing which showed typically the mode when classifying the image information of the unknown gamma ray simultaneously counted at the time of gamma ray coincidence processing into either information about true coincidence information or information about coincidence coincidence / scattering coincidence counting is there. (A), (b) is explanatory drawing which showed typically the event when an incident angle was changed in the combination which an opposing axis does not pass through the center axis of a ring.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... gamma ray detector 5 ... controller 6a ... coincidence pattern table 6b ... gamma ray coincidence processing program 10 ... reconstruction part M ... subject

Claims (6)

  A radiation coincidence processing method for performing a series of radiation coincidence processing including a coincidence counting step of simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, wherein (A) radiation generated from the subject is Simultaneously counting at the predetermined incident angle based on the output information for each incident angle obtained by detecting radiation by entering the radiation detector to be subjected to simultaneous detection and (B) simultaneous detection. And a counting separation step for separating the output information to be information related to true coincidence and the output information when simultaneously detected at other incident angles to be information related to incidental or scattered coincidence counting. And a radiation coincidence processing method.   A radiation coincidence processing program for causing a computer to execute a series of radiation coincidence processes including a coincidence counting step for simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, comprising: (A) the subject And (B) a predetermined incidence based on output information for each incident angle obtained by detecting the radiation incident on the radiation detector to be simultaneously detected. Count separation process that separates output information when detected simultaneously at an angle as information related to true coincidence, and output information when detected simultaneously at other incident angles as information related to incidental or scattered coincidence A radiation coincidence processing program for causing a computer to execute radiation coincidence processing including:   A computer-readable radiation that records a radiation coincidence processing program for causing a computer to execute a series of radiation coincidence processes including a coincidence counting step for simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered. It is a coincidence processing storage medium, which is obtained by (A) a coincidence counting step for simultaneously counting radiation generated from the subject, and (B) incident radiation detected on a radiation detector to be simultaneously detected. Based on the output information for each incident angle, the output information when it is simultaneously detected at a predetermined incident angle is used as information regarding the true coincidence, and the output information when it is simultaneously detected at other incident angles is accidental. Or for causing a computer to execute a radiation coincidence process including a separation process for separating so as to be information relating to scattering coincidence counting. Radiation coincidence processing storage medium characterized by storing a program.   A radiation coincidence counting device that simultaneously counts radiation generated from a subject to which a radiopharmaceutical is administered, (α) a radiation detector that detects incident radiation, and (β) radiation detection that is subject to simultaneous detection. Output information storage means for storing output information for each incident angle obtained by detecting radiation incident on the vessel, and (γ) based on the output information from the output information storage means, simultaneously at a predetermined incident angle Calculation means for performing calculation processing for separating the output information when detected into information regarding true coincidence and the output information when simultaneously detected at other incident angles as information regarding coincidence or scattering coincidence A radiation coincidence counting apparatus.   A nuclear medicine diagnostic apparatus using a radiation coincidence device for simultaneously counting radiation generated from a subject to which a radiopharmaceutical is administered, wherein (α) a radiation detector for detecting incident radiation, and (β) simultaneous Based on output information from the output information storage means, (γ) output information storage means for storing output information for each incident angle obtained by detecting radiation incident on a radiation detector to be detected The output information when simultaneously detected at a predetermined incident angle is regarded as information regarding true coincidence, and the output information when simultaneously detected at other incident angles is separated as information regarding incidental or scattered coincidence counting. And (δ) an image processing means for performing image processing based on information relating to the true coincidence separated by the calculation processing, obtained by the image processing means. Nuclear medicine diagnosis apparatus characterized by performing a nuclear medicine diagnosis based on the images. The storage medium which memorize | stored the output information for every incident angle obtained by injecting a radiation into the radiation detector used as the object of simultaneous detection described in Claim 1-5, and detecting it.

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