JP2020190446A - Calibration method of two-dimensional position map of radiation detector and radiation detector - Google Patents

Abstract

To provide a calibration method of a two-dimensional position map of a radiation detector, which can use both data on a photoelectric absorption event and a multiple scattering event.SOLUTION: A calibration method of a two-dimensional position map of a radiation detector includes a step of setting regions having high frequency of events as first regions 6a in which photoelectric absorption events have occurred and regions distributed between the first regions as second regions 6b in which multiple scattering events have occurred on a two-dimensional position map so as to create a first position reference table 6 obtained by calibrating the two-dimensional position map in a manner to be able to identify the first and second regions.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for calibrating a two-dimensional position map of a radiation detection device and a radiation detection device.

Conventionally, a scintillator element group consisting of a plurality of scintillator elements that convert detected radiation into an optical signal, and an optical sensor that receives an optical signal of the scintillator element that is optically coupled to the scintillator element group and incident with the converted radiation. In the radiation detection device configured by the above, a two-dimensional position map is created to determine the radiation detection position (for example, Patent Document 1).

In Patent Document 1, the two-dimensional position map irradiates the scintillator element group with radiation all at once, and calculates the center of gravity of the electric signal obtained by the optical sensor to calculate the two-dimensional coordinates (X) for the event in which each radiation is detected. , Y) Created by performing the calculation work.

Furthermore, in the acquired two-dimensional position map, the range detected by each scintillator element is determined by taking the minimum value of the peak of the signal intensity (pixel value) received by the optical sensor and dividing it at the location of the minimum value of the peak. The boundaries of each delimited detection position are determined.

Patent No. 4983981

Conventionally, when the irradiated radiation is incident on one scintillator element and the energy of the radiation is completely absorbed and detected (hereinafter referred to as a photoelectric absorption event), one radiation is scattered on a plurality of scintillator elements. It is known that there are cases where it is detected (hereinafter referred to as multiple scattering events). In the multiple scattering event, the amount of radiation energy detected for each scintillator element is lower than that in the photoelectric absorption event, but the total light output signal is the same as the photoelectric absorption event, so it cannot be distinguished. ..

Therefore, it is considered that Patent Document 1 does not distinguish between a photoelectric absorption event and a multiple scattering event on a two-dimensional position map. Then, although there are data of photoelectric absorption events and data of multiple scattering events as data for generating an image from the detected radiation, the timing characteristics for each event are not considered, so the characteristics of the detector. May get worse.

The present invention has been made to solve the above problems, and one object of the present invention is to provide a radiation detection device capable of using both photoelectric absorption event data and multiple scattering event data. The purpose of the present invention is to provide a method for calibrating a two-dimensional position map and a radiation detection device.

In order to achieve the above object, the method of calibrating the two-dimensional position map of the radiation detection device in the first aspect of the present invention is optically coupled to a scintillator element group composed of a plurality of scintillator elements and a scintillator element group. In a radiation detector including a radiation detector composed of one or more light receiving elements, the incident position of the radiation incident on the scintillator element is made to correspond to the frequency of the radiation event including the photoelectric absorption event and the multiple scattering event. It is a method of calibrating the two-dimensional position map of the radiation detection device that calibrates the represented two-dimensional position map. The region having a high frequency in the two-dimensional position map is set as the first region where the photoelectric absorption event is performed, and the first region By setting the region distributed between them as the second region where the multiple scattering event is performed, a first position reference table is created by calibrating the two-dimensional position map so that the first region and the second region can be distinguished. Have steps to do.

In the method for calibrating the two-dimensional position map of the radiation detection device in the first aspect of the present invention, as described above, the region having a high frequency in the two-dimensional position map is set as the first region where the photoelectric absorption event is performed, and the first region is used. The first position where the two-dimensional position map is calibrated so that the calibrated first region and the second region can be distinguished by setting the region distributed between the regions as the second region where the multiple scattering event is performed. Includes steps to create a lookup table. As a result, by referring to the first position reference table when creating the radiation image after calibration, the output of the optical signal due to the incident radiation is combined with the data in the first region where the photoelectric absorption event was performed and the multiple scattering event. It is possible to distinguish the data in the second region. As a result, it becomes possible to distinguish between the data of the photoelectric absorption event and the data of the multiple scattering event. Therefore, for example, the characteristics (timing, energy) of the detector can be corrected by correcting the second region where the multiple scattering event is performed differently from the data in the first region where the photoelectric absorption event is performed. ..

In the method for calibrating the two-dimensional position map of the radiation detection device according to the first aspect, the second position reference table in which the two-dimensional position map is calibrated is preferably divided into the number of scintillator elements. Further prepare for the steps to create. With this configuration, the position of the scintillator element can be associated with the position where the radiation is incident, so that the position of the scintillator element that has detected the radiation can be easily specified.

In the method of calibrating the two-dimensional position map of the radiation detection device according to the first aspect, preferably, in the step of creating the first position reference table obtained by calibrating the two-dimensional position map, the first position reference table has a grid pattern. The two-dimensional position map is divided into a plurality of areas so as to be such that, and among the plurality of areas divided in a grid pattern, the area surrounding the frequently used positions in the two-dimensional position map is set as the first area, and other than the first area. A step of creating a first position reference table in which the two-dimensional position map is calibrated by setting the area as the second area is included. With this configuration, the boundary between the first region and the second region can be easily created, so that it becomes easy to determine whether the photoelectric absorption event or the multiple scattering event has occurred in the scintillator element. ..

In the method of calibrating the two-dimensional position map of the radiation detection device according to the first aspect, preferably, the timing correction coefficient is calculated based on the first position reference table, and the two-dimensional position is calculated based on the calculated timing correction coefficient. Further, there is a step of creating a timing correction reference table in which the position map is calibrated. With this configuration, it is possible to more accurately determine the timing of radiation incident on the scintillator element, so it is possible to improve the performance of detecting the timing of radiation incident on the scintillator element of the radiation detection device. ..

In the method of calibrating the two-dimensional position map of the radiation detection device according to the first aspect, the energy correction coefficient is preferably calculated based on the first position reference table, and two-dimensional based on the calculated energy correction coefficient. It further provides a step to create an energy correction reference table with a calibrated position map. With this configuration, even if the linearity of the detector signal (the linearity of the signal output to the signal input to the light receiving element) is poor due to the light saturation of the light receiving element, etc., the radiation incident on the scintillator element It is possible to accurately grasp the energy value of. As a result, the radiographic image can be created only from the data capable of creating an accurate radiological image.

The radiation detector according to the second aspect of the present invention is a radiation detector composed of a scintillator element group composed of a plurality of scintillator elements and one or more light receiving elements optically coupled to the scintillator element group, and a control. The light receiving element detects the radiation radiated from the radiation source to the scintillator element and converts it into an output signal related to the optical signal, and the control unit acquires the output signal from the light receiving element and converts it into the acquired output signal. Based on this, a two-dimensional position map showing the frequency of radiation events including photoelectric absorption events and multiple scattering events and the incident position of the radiation incident on the scintillator element is created, and the frequently used region in the two-dimensional position map is displayed. By setting the first region where the photoelectric absorption event is performed and the region distributed between the first regions as the second region where the multiple scattering event is performed, the first region and the second region can be distinguished. It is configured to create a first position reference table in which the two-dimensional position map is calibrated.

As described above, in the radiation detection device according to the second aspect of the present invention, both the photoelectric absorption event data and the multiple scattering event data can be used as in the first aspect.

In the radiation detection device according to the second aspect, preferably, the control unit further creates a second position reference table in which the two-dimensional position map is calibrated by dividing the two-dimensional position map into the number of scintillator elements. It is configured to do. With this configuration, the arrangement of the scintillator element and the position where the radiation is incident can be associated with each other, so that the position of the scintillator element that has detected the radiation can be easily specified.

In the radiation detection device according to the second aspect, preferably, the control unit divides the first position reference table into a plurality of regions so as to form a grid pattern, and among the plurality of regions partitioned in a grid pattern. A first position reference table in which the two-dimensional position map is calibrated is created by setting the area surrounding the frequently used positions in the two-dimensional position map as the first area and the area other than the first area as the second area. It is configured in. With this configuration, the boundary between the first region and the second region can be easily created, so that it becomes easy to determine whether the photoelectric absorption event or the multiple scattering event has occurred in the scintillator element. ..

In the radiation detection device according to the second aspect, preferably, one light receiving element is provided for each of the plurality of scintillator elements. With this configuration, it is not necessary to provide light receiving elements according to the number of scintillator elements, so that the number of parts can be reduced.

In the radiation detection device according to the second aspect, preferably, the control unit calculates a timing correction coefficient from the magnitude of the output signal based on the first position reference table, and based on the calculated timing correction coefficient. It is configured to create a timing correction reference table that calibrates the two-dimensional position map. With this configuration, it is possible to more accurately determine the timing of radiation incident on the scintillator element, so it is possible to improve the performance of detecting the timing of radiation incident on the scintillator element of the radiation detection device. ..

In the radiation detection device according to the second aspect, preferably, the control unit calculates an energy correction coefficient from the magnitude of the output signal based on the first position reference table, and based on the calculated energy correction coefficient. It is configured to create an energy correction reference table that calibrates the 2D position map. With this configuration, even if the linearity of the detector signal (the linearity of the signal output to the signal input to the light receiving element) is poor due to the light saturation of the light receiving element, etc., the radiation incident on the scintillator element It is possible to accurately grasp the energy value of. As a result, the radiographic image can be created only from the data capable of creating an accurate radiological image.

According to the present invention, it is possible to distinguish between the photoelectric absorption event data and the multiple scattering event data as described above.

It is an overall block diagram which shows typically the structure of the PET apparatus by one Embodiment. It is a perspective view which shows typically the scintillator element and the light receiving element of the PET apparatus by one Embodiment. FIG. 3A is a cross-sectional view schematically showing a photoelectric absorption event. FIG. 3B is a graph schematically showing a multiple scattering event. It is a figure which showed the 2D position map by one Embodiment. It is a figure which showed the 1st position reference table by one Embodiment. It is a figure which showed the 2nd reference table by one Embodiment. It is a figure which showed typically the timing correction reference table by one Embodiment. It is a figure which showed typically the energy correction reference table by one Embodiment. It is a flowchart which shows the calibration method of the 2D position map by one Embodiment. It is a flowchart which shows the method of generating a PET image by one Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 10.

First, with reference to FIG. 1, the overall configuration of the radiation detection device 100 according to the present embodiment will be described. In the present embodiment, the case where the radiation detection device 100 is a PET (Positron Emission Tomography) device, which is one of the nuclear medicine devices, will be described.

As shown in FIG. 1, the radiation detection device 100 according to the embodiment of the present invention includes a scintillator element group 1, a radiation detector 3 including a light receiving element 2, and a control unit 4.

As shown in FIG. 1, the radiation detection device 100 is a device that captures an image of the inside of a subject (human body or the like) using a drug labeled with a positron emitting nuclide. Specifically, the radiation detection device 100 is configured to acquire the position where the drug pair annihilation occurs by detecting a pair of gamma rays (radiation) generated by the pair annihilation of the positron and the electron generated by the drug. Has been done. Since a pair of gamma rays are detected by a pair of radiation detectors 3, a line (LOR: Line Of Response) connecting the pair of radiation detectors 3 that have detected gamma rays is drawn to make a diagnosis target such as a cancer cell. The position appears as the intersection of multiple LORs. Then, the radiation detection device 100 is configured to form (photograph) an image of the inside of the subject by acquiring a plurality of positions where the pair annihilation of the drug has occurred. Then, the formed image is used for image diagnosis such as the presence or absence of cancer cells by utilizing the fact that the drug is easily accumulated.

Further, the radiation detection device 100 is configured to photograph a subject in the supine position. Specifically, a plurality of radiation detection devices 100 are arranged so as to surround the subject in a state where the light receiving element 2 is directed to the body axis of the subject (the axis extending from the head to the legs). .. Further, a plurality of radiation detection devices 100 are arranged in the same configuration in the direction in which the body axis of the subject (not shown) extends (in the depth direction of the paper surface). Here, the gamma ray generated by the pair annihilation of the drug is radiation of 511 keV, and cannot be directly detected by using the light receiving element 2. Therefore, a scintillator element group 1 is provided between the subject and the light receiving element 2. As a result, when a gamma ray is incident on the scintillator element group 1, the phosphor in the scintillator element group 1 emits light by the gamma ray, and an optical signal (fluorescence) is generated. The radiation detection device 100 is configured to detect an optical signal emitted by the gamma ray.

As shown in FIGS. 1 and 2, the radiation detection device 100 includes a scintillator element group 1 including a plurality of scintillator elements 1a that emit an optical signal based on the reception of gamma rays having a predetermined energy amount. The scintillator element group 1 is a collection of a plurality of scintillator elements 1a. The scintillator element group 1 is composed of, for example, a group of 9 rows and 10 columns (90 pieces) of scintillator elements 1a.

When the scintillator element 1a absorbs a gamma ray of 511 keV, the optical signal emitted corresponds to, for example, 10,000 or more photons. Gamma rays may enter the inside of another scintillator element 1a. The scintillator element 1a includes, for example, LSO (Lu ₂ SiO ₅ ), LYSO (Lu _(2-x) Y _x SiO ₅ ), LGSO (Lu _(2-x) Gd _x SiO ₅ ), LuAG (Lu ₃ Al ₅ O). ₁₂ ), it is composed of crystals such as LFS (Lutetium Fine Scintillator).

Further, the radiation detector 3 includes a plurality of light receiving elements (photoelectric conversion elements) 2 that output an output signal based on the incidentness of the optical signal. The light receiving element 2 includes, for example, an avalanche photodiode (APD) and a quenching resistor. An avalanche photodiode is a photodiode in which a voltage larger than the breakdown voltage is applied to the reverse bias, and is normally in a state in which no current flows. Since an avalanche photodiode causes a large current to flow when a photon is incident, it can output an output signal having a good S / N ratio in a unit of one photon. Further, since the quenching resistor is connected in series with the avalanche photodiode and a voltage is applied by the current flowing from the avalanche photodiode, the voltage applied to the avalanche photodiode is lowered to less than the breakdown voltage. This stops the current flowing through the avalanche photodiode and returns it to a state where photons can be detected again.

The light receiving element 2 detects a photon of an optical signal incident on the position of the light receiving element 2 and outputs an output signal. The output signal reflecting the number of photons output from the plurality of light receiving elements 2 represents the energy information of the optical signal based on the gamma rays incident on the scintillator element 1a. Further, from the time when the signal is acquired, the incident time of gamma rays and the flight time from the generation of gamma rays to the incident calculated from the incident time can also be acquired. One light receiving element 2 is provided for each of the plurality of scintillator elements 1a.

As shown in FIG. 3A, when all the gamma rays incident on one scintillator element 1a react inside the scintillator element 1a, an optical signal having an energy corresponding to 511 keV is generated. A radiation event that detects an optical signal corresponding to the total energy of incident gamma rays is defined as a photoelectric absorption event.

On the other hand, as shown in FIG. 3B, incident gamma rays may react across a plurality of scintillator elements 1a. In the reaction A, the gamma rays incident on the scintillator element 1a collide with the electrons of the substance in the scintillator element 1a and cause the electrons to recoil. Gamma rays give a part of energy to electrons and are scattered and ejected to the outside of the scintillator element 1a. Such scattering of gamma rays due to the recoil of electrons is called Compton scattering. The recoiled electron generates an optical signal having an energy equivalent to the energy finally given, and returns to the original energy state.

Further, in FIG. 3B, the gamma rays blown off by the electrons in the reaction A have high energy and therefore penetrate into the inside of another adjacent scintillator element 1a. Then, in the reaction B, a detection reaction occurs in the adjacent scintillator element 1a, and an optical signal is generated. In this way, a radiation event in which incident gamma rays react with a plurality of scintillator elements 1a and an optical signal is detected by the light receiving element 2 is defined as a multiple scattering event. In some cases, gamma rays that collide with electrons and jump out react again in the same scintillator element 1a and are finally converted into optical signals corresponding to all energies (511 keV) in the same scintillator element 1a. is there. In this case, it is a photoelectric absorption event.

As shown in FIG. 1, the radiation detection device 100 includes a control unit 4 that acquires an output signal output by the light receiving element 2. The control unit 4 includes a storage means 41, a main control means 42, a signal processing means 43, and an image processing means 44. Further, the control unit 4 includes an information processing device such as a PC (personal computer).

The storage means 41 is composed of an HDD (hard disk drive), a memory, and the like. Further, the storage means 41 stores various programs executed by the main control means 42 and the signal processing means 43, captured image data, and true measured values and theoretical values of predetermined gamma rays required for signal correction described later. Various data including are stored.

The main control means 42 is composed of a CPU (Central Processing Unit) and the like. Further, the main control means 42 causes the CPU to function as the control unit 4 of the radiation detection device 100 by executing the control program stored in the storage means 41. In addition, the main control means 42 controls the radiation detection device 100 (for example, the movement of the bed portion on which the subject lies down).

The image processing means 44 creates a PET image (radiation image) based on the output signal and the correction output signal output from the signal processing means 43. The optical signal generated by the incident of two gamma rays emitted in opposite directions of approximately 180 degrees generated by annihilation is simultaneously detected by the two opposing light receiving elements 2. Therefore, it can be seen that gamma rays are generated at any position on the path of the two opposing light receiving elements 2 and are incident on the photodetector. Since the time resolution of the conventional radiation detection device 100 is insufficient, it is not possible to grasp the pair annihilation at any position on the path with sufficient accuracy. Therefore, a plurality of these radiation paths are collected, and the region where the paths intersect is used as a source of gamma rays and displayed as an image.

The image processing means 44 has a function of calculating the two-dimensional coordinates (X, Y) of the scintillator element 1a that has detected each gamma ray by calculating the center of gravity of the output signal acquired from the light receiving element 2.

The image processing means 44 creates a two-dimensional position map 5 based on the two-dimensional coordinates (X, Y) of the scintillator element 1a that has detected each gamma ray, and specifies the position of the scintillator element 1a that has detected the gamma ray. Hereinafter, the creation of the two-dimensional position map 5 and the calibration method of the two-dimensional position map 5 will be described in detail.

FIG. 4 shows an example of the two-dimensional position map 5. The two-dimensional position map 5 is created by irradiating the scintillator element group 1 with radiation all at once before creating the PET image. The image processing means 44 creates a two-dimensional position map 5 based on the two-dimensional coordinates (X, Y) of the scintillator element 1a that has detected each gamma ray. The two-dimensional position map 5 is created by associating the incident position of the gamma ray incident on the scintillator element 1a with the frequency (pixel value) of the radiation event including the photoelectric absorption event and the multiple scattering event.

The circled part of the area surrounded by the broken line represents the part where the photoelectric absorption event occurred, and the other part represents the part where the multiple scattering event occurred. As described above, since the probability of occurrence of the photoelectric absorption event is higher than that of the multiple scattering event, the frequency (pixel value) on the two-dimensional position map 5 is higher than that of the surroundings. On the other hand, since the probability of occurrence of the multiple scattering event is lower than that of the photoelectric absorption event, the frequency (pixel value) on the two-dimensional position map 5 is smaller than the position where the photoelectric absorption event is performed.

Here, in the image processing means 44 of the radiation detection device 100 of the present embodiment, as shown in FIG. 5, a region having a high frequency in the two-dimensional position map 5 is designated as a first region 6a in which the photoelectric absorption event is performed. The region distributed between the first regions 6a is defined as the second region 6b where the multiple scattering event is performed. In this way, the first position reference table 6 for identifying the first region 6a and the second region 6b obtained by calibrating the two-dimensional position map 5 is created.

The two-dimensional position map 5 is divided into a plurality of regions so that the first position reference table 6 to be created has a grid pattern, and the frequencies (pixels) of the plurality of scintillator elements 1a among the plurality of regions partitioned in a grid pattern. The region surrounding the position (position represented by the black circle) having a large value) is referred to as the first region 6a, and the region other than the first region 6a is referred to as the second region 6b. In this way, the first position reference table 6 in which the two-dimensional position map 5 is calibrated is created. At this time, the first region 6a is formed on a rectangle centered on the maximum value of the frequency (pixel value). The length of the side of the first region 6a is set to a predetermined size based on experiments and empirical rules, that is, the size of the first region 6a is common to each first region 6a. is there. The size of the first region 6a may be different in each first region 6a.

Further, in the image processing means 44 of the radiation detection device 100 of the present embodiment, the maximum value of the frequency (pixel value) of the two-dimensional position map 5 is obtained, and the middle line of each maximum value is drawn as shown in FIG. A second position reference table 7 is created by calibrating the two-dimensional position map 5. The scintillator elements 1a represented by (A) to (C) in FIG. 6 correspond to the positions of the scintillator elements 1a represented by (A) to (C) in FIG.

Further, in the image processing means 44 of the radiation detection device 100 of the present invention, the scintillator element 1a shines due to the incident of radiation based on the magnitude of the output signal related to the optical signal from the light receiving element 2 based on the first position reference table 6. A timing correction coefficient for correcting the timing is calculated, and a timing correction reference table 8 is created by calibrating the two-dimensional position map 5 based on the calculated timing correction coefficient. FIG. 7 is a diagram schematically showing the timing correction reference table 8, in which the region 8a where the photoelectric absorption event is performed is represented by a square, and the region 8b where the multiple scattering event is performed is represented by a rectangle. The region where the photoelectric absorption event is performed and the region where the multiple scattering event is performed correspond to each other between the first position reference table 6 and the timing correction reference table 8.

The correction coefficient is different between the region 8a where the photoelectric absorption event is performed and the region 8b where the multiple scattering event is performed. For example, in the case of the region 8a where the photoelectric absorption event has occurred, since the optical signal corresponding to the energy of 511 keV is detected by the incident of the gamma ray as described above, the light receiving element 2 tends to be saturated and the linearity is deteriorated. In a multiple scattering event, each light receiving element 2 detects an optical signal corresponding to an energy of less than 511 keV, so that light saturation of the light receiving element 2 is unlikely to occur. The larger the detected optical signal, the faster the signal is transmitted on the circuit, so that the timing when the signal is detected can be accurately known. Therefore, the timing detection is more accurate in the first region 6a representing the photoelectric absorption event having a large energy to be detected than in the second region 6b representing the multiple scattering event. Even when gamma rays are simultaneously incident on the scintillator element 1a, it is conceivable that the transmission time of the signal on the circuit may be deviated. Therefore, the correction coefficient is determined at each location in order to align the timing.

On the other hand, in the region 8b where the multiple scattering event is performed, the respective optical signals detected by the plurality of light receiving elements 2 are small, so that the signal transmission on the circuit is delayed, and the timing is delayed accordingly. Therefore, in the region 8b where the multiple scattering event is performed, a correction value for correcting the deviation is determined from the ratio of the light energy and the timing. Further, since the amount of deviation differs depending on the position of the region 8b where the multiple scattering event is performed, the correction coefficient is determined at each position.

For example, in the region 8a where a certain photoelectric absorption event is performed, a correction value of -1 is provided. Alternatively, in the region 8b where a certain multiple scattering event has occurred, a correction value of +1 is provided. In this way, the correction value at each position is determined. The created timing correction reference table 8 is stored in the storage means 41.

Further, the image processing means 44 has energy for correcting the magnitude of the output signal related to the optical signal from the light receiving element 2 to the energy value of the radiation incident on the scintillator element 1a based on the first position reference table 6. Calculate the correction factor. An energy correction reference table 9 is created by calibrating the two-dimensional position map 5 based on the calculated energy correction coefficient. FIG. 8 is a diagram schematically showing the energy correction reference table 9, in which the region 9a where the photoelectric absorption event is performed is represented by a square, and the region 9b where the multiple scattering event is performed is represented by a rectangle. The region where the photoelectric absorption event is performed and the region where the multiple scattering event is performed correspond to each other between the first position reference table 6 and the energy correction reference table 9.

The amount of the optical signal received by the light receiving element 2 is different between the region 9a where the photoelectric absorption event is performed and the region 9b where the multiple scattering event is performed. For example, in the case of the region 9a where the photoelectric absorption event is performed, the light receiving element 2 is saturated because strong light corresponding to the energy of 511 keV enters as described above, whereas in the region 9b where the multiple scattering event is performed. Each light receiving element 2 detects an optical signal corresponding to an energy of less than 511 keV. Then, the region 9b in which the multiple scattering event is performed has a different linearity from the region 9a in which the photoelectric absorption event is performed. As a result, the correction value is different from that of the region 9a where the light absorption event is performed. As shown in FIG. 8, the correction value is represented by an optical signal × variable (m or n). Variables are determined based on the ratio of energy to optical signal. The created energy correction reference table 9 is stored in the storage means 41.

The image processing means 44 may be an arithmetic processing unit dedicated to image processing, or may function as the image processing means 44 by causing the CPU to execute a signal processing and an image processing program, respectively. Further, a device dedicated to image processing may be provided as the image processing means 44.

Next, a method of calibrating the two-dimensional position map 5 of the radiation detection device 100 and a method of generating a PET image based on the data obtained by the calibration method according to the embodiment will be described with reference to FIGS. 9 and 10.

As shown in FIG. 9, in step S1, the user irradiates the radiation detector 3 with radiation from the radiation source in order to create the two-dimensional position map 5. At this time, by arranging the radiation source in the center, the radiation emitted to the radiation detectors 3 arranged at an angle of 180 degrees from the radiation source reaches the plurality of radiation detectors 3 at the same time. In step S2, the radiation detected by the scintillator element 1a constituting the radiation detector 3 is converted into an optical signal. When converting to an optical signal, weak light is emitted from the scintillator element 1a.

In step S3, the light receiving element 2 detects the optical signal emitted from the scintillator element 1a. In step S4, the control unit 4 calculates the output signal output from the light receiving element 2 and creates the two-dimensional position map 5.

In step S5, the control unit 4 creates a first position reference table 6 capable of distinguishing the first region 6a and the second region 6b obtained by calibrating the two-dimensional position map 5. At this time, the two-dimensional position map 5 is divided into a plurality of regions so that the first position reference table 6 has a grid pattern, and the two-dimensional positions of the plurality of scintillator elements 1a among the plurality of regions partitioned in a grid pattern. The first position reference table 6 in which the two-dimensional position map 5 is calibrated is set as the first area 6a as the area surrounding the frequently used positions on the map 5 and the second area 6b as the area other than the first area 6a. create.

In step S6, the control unit 4 creates a second position reference table 7 in which the two-dimensional position map 5 is calibrated.

In step S7, the control unit 4 has energy for correcting the magnitude of the optical signal output from the light receiving element 2 to the energy value of the radiation incident on the scintillator element 1a for each region of the first position reference table 6. Calculate the correction factor. In step S8, the control unit 4 creates an energy correction reference table 9 in which the two-dimensional position map 5 is calibrated based on the correction value calculated in step S7. In step S9, the control unit 4 calculates the timing correction coefficient for each region of the first position reference table 6. In step S10, the control unit 4 creates a timing correction reference table 8 in which the two-dimensional position map 5 is calibrated based on the correction value calculated in step S9. The above is the calibration method of the two-dimensional position map 5 according to the present embodiment. The created timing correction reference table 8 is stored in the storage means 41. The order in which the energy correction reference table 9 and the timing correction reference table 8 are created is not limited to the case where the energy correction reference table 9 is created first, and the energy correction reference table 9 and the timing correction reference table 8 are created. May be created at the same time, or the timing correction reference table 8 may be created first.

Next, a method of generating a PET image will be described with reference to FIG. 10 using the timing correction reference table 8 and the energy correction reference table 9.

In step S11, the user administers the drug to the subject. In step S12, the scintillator element 1a detects gamma rays. In step S13, the control unit 4 determines the position of the scintillator element 1a that has detected the gamma ray based on the two-dimensional coordinates (X, Y) of the scintillator element 1a that has detected the gamma ray by the second position reference table 7. .. In step S14, the control unit 4 refers to the timing correction reference table 8 and the energy correction reference table 9 and corrects the energy amount and the timing based on the correction value according to the position of the scintillator element 1a in which the radiation is incident. ..

In step S15, the control unit 4 determines whether or not the corrected energy amount is 511 keV. If it is 511 keV, the process proceeds to the next step S16, but if it is different, the process returns to step S12 without using this signal. In the case of a region where a multiple scattering event has occurred, the determination is made using the sum of the values of the regions where gamma rays are detected. In step S16, the control unit 4 determines if there is a pair of corresponding detections that detect the two gamma rays emitted at 180 degrees. If there is a pair of corresponding detections, the process proceeds to the next step S17, but if there is no detection, the process returns to step S12. In step S17, the control unit 4 determines whether the timings of the pair of corresponding detections match. If they match, the process proceeds to the next step S18. If they do not match, the radiation is not emitted from the same radiation source, so this signal is not used and the process returns to step S12.

In step S18, the control unit 4 generates a PET image from the obtained data.

(Effect of this embodiment)
In this embodiment, the following effects can be obtained.

In the present embodiment, as described above, the region having a high frequency in the two-dimensional position map 5 is the first region 6a where the photoelectric absorption event is performed, and the region distributed between the first regions 6a is the multiple scattering event. A step of creating a first position reference table 6 in which the two-dimensional position map 5 is calibrated so that the first area 6a and the second area 6b can be distinguished by using the divided second area 6b is provided. As a result, by referring to the first position reference table 6 at the time of creating the radiation image after calibration, the data of the first region 6a in which the photoelectric absorption event was performed and the multiple scattering event can be obtained from the optical signal output due to the incident radiation. It is possible to distinguish from the data of the second region 6b performed. As a result, it becomes possible to distinguish between the photoelectric absorption event data and the multiple scattering event data. Therefore, for example, the characteristics (timing, energy) of the detector are corrected by correcting the second region 6b in which the multiple scattering event is performed differently from the data in the first region 6a in which the photoelectric absorption event is performed. Can be done.

Further, the present embodiment further includes a step of creating a second position reference table 7 in which the two-dimensional position map 5 is calibrated by dividing the two-dimensional position map 5 into the number of scintillator elements as described above. By doing so, since the positions of the plurality of scintillator elements 1a and the positions where the radiation is incident can be associated with each other, the positions of the scintillator elements 1a that have detected the radiation can be easily specified.

Further, in the present embodiment, as described above, the step of creating the first position reference table 6 in which the two-dimensional position map 5 is calibrated is a two-dimensional position so that the first position reference table 6 has a grid pattern. The map 5 is divided into a plurality of regions, and among the plurality of regions partitioned in a grid pattern, the region surrounding the frequently used positions in the two-dimensional position map 5 is designated as the first region 6a, and the regions other than the first region 6a are the first regions. It includes a step of creating a first position reference table 6 in which the two-dimensional position map 5 is calibrated by setting the two regions 6b. By doing so, the boundary between the first region 6a and the second region 6b can be easily created, so that it is determined whether the photoelectric absorption event or the multiple scattering event is performed in the scintillator element 1a. It becomes easier to do.

Further, in the present embodiment, as described above, the timing correction coefficient is calculated based on the first position reference table 6, and the two-dimensional position map 5 is calibrated based on the calculated timing correction coefficient. It further comprises a step of creating a table 8. By doing so, it is possible to more accurately determine the timing at which the radiation is incident on the scintillator element 1a, and thus the performance of detecting the timing at which the radiation is incident on the scintillator element 1a of the radiation detection device 100 is improved. Can be done.

Further, in the present embodiment, the energy correction coefficient is calculated based on the first position reference table 6, and the energy correction reference table 9 is created by calibrating the two-dimensional position map 5 based on the calculated energy correction coefficient. Prepare more steps. As a result, even when the linearity of the detector signal is poor due to light saturation of the light receiving element 2, it is possible to accurately grasp the energy value of the radiation incident on the scintillator element 1a. As a result, the radiographic image can be created only from the data capable of creating an accurate radiological image.

Further, in the present embodiment, as described above, a radiation detector composed of a scintillator element group 1 composed of a plurality of scintillator elements 1a and one or more light receiving elements 2 optically coupled to the scintillator element group 1. 3 and a control unit 4, the light receiving element 2 detects the radiation radiated from the radiation source to the scintillator element 1a and converts it into an output signal related to an optical signal, and the control unit 4 receives an output signal from the light receiving element 2. Is acquired, and based on the acquired output signal, a two-dimensional position map 5 showing the frequency of radiation events including photoelectric absorption events and multiple scattering events and the incident position of the radiation incident on the scintillator element 1a is created. The region with high frequency in the two-dimensional position map 5 is defined as the first region 6a in which the photoelectric absorption event is performed, and the region distributed between the first regions 6a is designated as the second region 6b in which the multiple scattering event is performed. The first position reference table 6 is configured by calibrating the two-dimensional position map 5 so that the first area 6a and the second area 6b can be distinguished from each other. As a result, it is possible to separately acquire the data in the first region 6a in which the photoelectric absorption event is performed and the data in the second region 6b in which the multiple scattering event is performed. As a result, both photoelectric absorption event data and multiple scattering event data can be used. For example, by correcting the data in the second region 6b where the multiple scattering event is performed, it can be used in the same manner as the data in the first region 6a where the photoelectric absorption event is performed.

Further, in the present embodiment, as described above, the control unit 4 calibrates the two-dimensional position map 5 by dividing the two-dimensional position map 5 into the number of scintillator elements 1a of the two-dimensional position map 5. Is configured to create more. In this way, since the arrangement of the plurality of scintillator elements 1a can be associated with the position where the radiation is incident, the position of the scintillator element 1a that has detected the radiation can be easily specified.

Further, in the present embodiment, as described above, the control unit 4 divides the first position reference table 6 into a plurality of regions so as to form a grid pattern, and among the plurality of regions partitioned in a grid pattern, The first position reference obtained by calibrating the two-dimensional position map 5 by defining the region surrounding the frequently used positions in the two-dimensional position map 5 as the first region 6a and the regions other than the first region 6a as the second region 6b. It is configured to create table 6. In this way, the boundary between the first region 6a and the second region 6b can be easily created, so that it is determined whether the photoelectric absorption event or the multiple scattering event is performed in the scintillator element 1a. It will be easier.

Further, in the present embodiment, one light receiving element 2 is provided for each of the plurality of scintillator elements 1a. As a result, the number of parts can be reduced because the light receiving elements 2 do not have to be provided according to the number of scintillator elements 1a.

Further, in the present embodiment, the control unit 4 calculates a timing correction coefficient from the magnitude of the output signal based on the first position reference table 6, and the two-dimensional position map 5 is based on the calculated timing correction coefficient. Is configured to create a timing correction reference table 8 calibrated. As a result, the timing at which the radiation is incident on the scintillator element 1a can be determined more accurately, so that the performance of detecting the timing at which the radiation is incident on the scintillator element 1a of the radiation detection device 100 can be improved.

Further, in the present embodiment, the control unit 4 calculates an energy correction coefficient from the magnitude of the output signal based on the first position reference table 6, and the two-dimensional position map 5 is based on the calculated energy correction coefficient. It is configured to create an energy correction reference table 9 calibrated. As a result, even if the linearity of the detector signal (the linearity of the signal output with respect to the signal input to the light receiving element 2) is poor due to the light saturation of the light receiving element 2, the radiation incident on the scintillator element 2a It is possible to accurately grasp the energy value. As a result, the radiographic image can be created only from the data capable of creating an accurate radiological image.

[Modification example]
It should be noted that the embodiments disclosed this time are exemplary in all respects and are not considered to be restrictive. The scope of the present invention is shown by the scope of claims rather than the description of the above-described embodiment, and further includes all modifications (modifications) within the meaning and scope equivalent to the scope of claims.

For example, in the above embodiment, an example in which a PET device is used as a radiation detection device has been shown, but the present invention is not limited to this. For example, as the radiation detection device, a SPECT (single photon emission CT) device or a TOF (Time-of-Flight) PET device may be used.

For example, in the above embodiment, an example in which the first position reference table is arranged in a grid pattern is shown, but the present invention is not limited to this. For example, the region where the photoelectric absorption event occurred may be circled, and the region where the multiple scattering event occurred may be represented by a line.

For example, in the above embodiment, the region where the photoelectric absorption event is performed is represented by a square and the region where the multiple scattering event is performed is represented by a rectangle in the timing correction reference table, but the present invention is limited to this. Absent. For example, it may be represented by a circle.

For example, in the above embodiment, the region where the photoelectric absorption event is performed is represented by a square and the region where the multiple scattering event is performed is represented by a rectangle in the energy correction reference table, but the present invention is limited to this. Absent. For example, it may be represented by a circle.

For example, in the above embodiment, an example in which one light receiving element is provided for a plurality of scintillator elements is shown, but the present invention is not limited to this. For example, light receiving elements may be provided according to the number of scintillator elements.

For example, in the above embodiment, the reflector is not provided between the plurality of scintillator elements, but the present invention is not limited to this. For example, a reflector may be provided between the scintillator elements.

Further, in the above embodiment, for convenience of explanation, the processing of the control unit has been described using a flow-driven flow in which the processing of the control unit is sequentially performed along the processing flow. For example, the processing operation of the control unit is performed in event units. It may be performed by an event-driven type (event-driven type) process that executes the process. In this case, it may be completely event-driven, or it may be a combination of event-driven and flow-driven.

For example, in the above embodiment, an example of creating a timing correction reference table and an energy reference table has been shown, but the present invention is not limited to this. For example, it is not necessary to create a timing correction reference table and an energy reference table.

1 Scintillator element group 1a Scintillator element 2 Light receiving element 3 Radiation detector 4 Control unit 5 Two-dimensional position map 6 First position reference table 7 Second position reference table 8 Timing correction reference table 9 Energy correction reference table 100 Radiation detector

Claims (11)

In a radiation detector including a radiation detector composed of a scintillator element group composed of a plurality of scintillator elements and one or more light receiving elements optically coupled to the scintillator element group, radiation incident on the scintillator element. This is a method for calibrating a two-dimensional position map of a radiation detection device that calibrates a two-dimensional position map that represents the incident position of the radiation event and the frequency of radiation events including photoelectric absorption events and multiple scattering events.
The region with high frequency in the two-dimensional position map is designated as the first region where the photoelectric absorption event is performed, and the region distributed between the first regions is designated as the second region where the multiple scattering event is performed. A method for calibrating a two-dimensional position map of a radiation detection device, comprising a step of creating a first position reference table in which the two-dimensional position map is calibrated so that the first region and the second region can be distinguished. 2. The radiation detection apparatus according to claim 1, further comprising a step of creating a second position reference table obtained by calibrating the two-dimensional position map by dividing the two-dimensional position map into the number of scintillator elements. How to calibrate a dimensional position map. The step of creating the first position reference table obtained by calibrating the two-dimensional position map divides the two-dimensional position map into a plurality of regions so that the first position reference table has a grid pattern. The two-dimensional position map is calibrated by setting a region surrounding a frequently-used position in the plurality of two-dimensional position maps divided into the first regions as the first region and a region other than the first region as the second region. The method of calibrating a two-dimensional position map of a radiation detector according to claim 1 or 2, comprising the step of creating a first position reference table. The claim further comprises a step of calculating a timing correction coefficient based on the first position reference table and creating a timing correction reference table obtained by calibrating the two-dimensional position map based on the calculated timing correction coefficient. The method for calibrating a two-dimensional position map of the radiation detection device according to any one of 1 to 3. The claim further comprises a step of calculating an energy correction coefficient based on the first position reference table and creating an energy correction reference table obtained by calibrating the two-dimensional position map based on the calculated energy correction coefficient. The method for calibrating a two-dimensional position map of the radiation detection device according to any one of 1 to 4. A radiation detector composed of a scintillator element group composed of a plurality of scintillator elements and one or more light receiving elements optically coupled to the scintillator element group.
Equipped with a control unit
The light receiving element detects the radiation emitted from the radiation source to the scintillator element, converts it into an output signal related to an optical signal, and converts it into an output signal.
The control unit acquires the output signal from the light receiving element, and based on the acquired output signal, determines the frequency of radiation events including photoelectric absorption events and multiple scattering events and the incident position of radiation incident on the scintillator element. A two-dimensional position map represented in correspondence is created, the region with high frequency in the two-dimensional position map is set as the first region where the photoelectric absorption event is performed, and the region distributed between the first regions is the multiple scattering event. The second region is configured to create a first position reference table in which the two-dimensional position map is calibrated so that the first region and the second region can be distinguished from each other. There is a radiation detector. 6. The control unit is configured to further create a second position reference table obtained by calibrating the two-dimensional position map by dividing the two-dimensional position map into the number of the scintillator elements. The radiation detector according to. The control unit divides the first position reference table into a plurality of regions so as to form a grid pattern, and among the plurality of regions partitioned in a grid pattern, frequently used positions in the plurality of the two-dimensional position maps. By setting the area surrounding the area as the first area and the area other than the first area as the second area, the first position reference table obtained by calibrating the two-dimensional position map is created. The radiation detection apparatus according to claim 6 or 7. The radiation detection device according to any one of claims 6 to 8, wherein one light receiving element is provided for each of the plurality of scintillator elements. The control unit calculates a timing correction coefficient from the magnitude of the output signal based on the first position reference table, and calibrates the two-dimensional position map based on the calculated timing correction coefficient. The radiation detection apparatus according to any one of claims 6 to 9, which is configured to create a reference table. The control unit calculates an energy correction coefficient from the magnitude of the output signal based on the first position reference table, and calibrates the two-dimensional position map based on the calculated energy correction coefficient. The radiation detection apparatus according to any one of claims 6 to 10, which is configured to create a reference table.

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