JP2020027081A - Gamma camera - Google Patents

Abstract

To achieve gamma cameras that can highly sensitively measure a three-dimensional concentration distribution of a radioactive substance in a short time even when a measurement object is a high density substance.SOLUTION: A gamma camera 100 is configured to: calculate an energy change and direction change of a gamma ray scattered inside a measurement object on the basis of incident direction information and energy information on a gamma ray acquired by a radiation detector, physical information on a measurement object acquired by a physical information acquisition device, and measurement condition information on the radiation detector acquired by a measurement condition acquisition device; restrict a distribution area of a radioactive substance; and further restrict the distribution area of the radioactive substance due to weighting by a scattering probability and absorption probability calculated based on the physical information of the measurement object. Accordingly, even when the measurement object is a high density substance, the gamma camera can highly sensitively measure a three-dimensional concentration distribution of the radioactive substance in a short time.SELECTED DRAWING: Figure 7

Description

  The present application relates to a gamma camera for measuring a three-dimensional concentration distribution of a radioactive substance.

  Conventionally, a gamma camera is used for measuring the concentration distribution of a radioactive substance, but it is difficult to measure the distribution in the depth direction, and a method of measuring a three-dimensional concentration distribution with one gamma camera has been studied. For example, in Patent Literature 1, a single gamma camera is used to capture two images on imaging axes inclined at the same angle to the left and right from a vertical line with respect to the front of the measurement target, and a stereoscopic image is obtained from the obtained two images. Have gained.

  As a method for imaging the three-dimensional distribution of a gamma ray source, a method using a Compton camera is known. A typical Compton camera is equipped with two radiation detectors, and focuses on events in which gamma rays from a gamma ray source are Compton-scattered by the first detector and then photoelectrically absorbed by the second detector. The three-dimensional distribution of the gamma ray source is imaged based on the detection position and the detected energy of the gamma ray in the detector.

  As a measuring method using this Compton camera, for example, in Patent Document 2, a radiation measuring apparatus having two detection units arranged in front and rear as viewed from the radiation generation side is used to measure a position of a scattering point, a position of an absorption point, and radiation energy. Thus, the position of the radiation source is specified as a conical surface (Compton cone) having the scattering point as the vertex.

  Patent Document 3 discloses an image based on a maximum likelihood estimation expectation value maximization method (ML-EM method), which is a statistical method, as a method for optimizing a three-dimensional distribution image of a gamma ray source by a Compton camera. A reconstruction method is shown. Further, Non-Patent Document 1 discloses a list mode maximum likelihood reconstruction method (LM-ML-EM method) of Compton scattering camera images in nuclear medicine. According to the LM-ML-EM method, even when it is difficult to obtain a gamma ray source distribution in space from observed gamma ray measurement data by maximum likelihood estimation, the expected value of likelihood is maximized by iterative calculation. It is possible to obtain the gamma ray source distribution.

JP-A-9-218268 JP 2011-85418 A WO2006-035706

S. J. Wilderman, N.W. H. Clinthorne, J .; A. Fessler, and W.W. L. Rogers, "List-mode maximum likelihood reconstruction of Compton scatter camera image in nuclear medicine", IEEE Nucl. Sci. Symp. , 1998, vol. 3, pp. 1716-1720.

  In conventional gamma cameras, to measure the three-dimensional concentration distribution of radioactive materials, only gamma rays directly incident from radioactive materials are used as data, and gamma rays scattered between radioactive materials and radiation detectors are detected. Is not used as data. On the other hand, when the measurement target is a substance having a higher density than the human body, for example, concrete or metal, most of the gamma rays are scattered inside the object of the high-density substance. For this reason, the conventional gamma camera has a problem that it is difficult to measure the three-dimensional concentration distribution of the radioactive substance when the measurement target is a high-density substance.

  As a method for measuring the three-dimensional concentration distribution of a radioactive substance in a measurement object, in a method in which one gamma camera is moved and measurement is performed a plurality of times as in Patent Document 1, the gamma camera is connected to a driving unit and moved. There is a problem that a mechanism for performing the measurement is required, and the measurement time becomes long because the measurement is performed a plurality of times. In the methods of Patent Documents 2, 3 and Non-Patent Document 1, the three-dimensional concentration distribution of the radioactive material is measured by one measurement with one gamma camera, but the measurement using Compton scattering is performed. The method is a method applied only to a so-called Compton camera.

  The present application discloses a technique for solving the above-described problem, and even when the measurement target is a high-density substance, it is possible to measure the three-dimensional concentration distribution of the radioactive substance with high sensitivity in a short time. The aim is to obtain a possible gamma camera.

  The gamma camera disclosed in the present application, a radiation detector that detects the incident direction and energy of gamma rays coming from the measurement target, a gamma ray data storage unit that stores the incident direction information and energy information acquired by the radiation detector, Physical property information acquisition device that acquires physical property information including at least the component and density of the measurement target, a physical property information storage unit that stores the physical property information of the measurement target acquired by the physical property information acquisition device, and measurement condition information of the radiation detector. The measurement condition acquisition device to be acquired, the measurement condition storage unit that stores the measurement condition information acquired by the measurement condition acquisition device, the incident direction information and the energy information stored in the gamma ray data storage unit, and the physical property information storage unit Based on the physical property information and the measurement condition information stored in the measurement condition storage unit. Calculate the energy change and direction change, those having a three-dimensional distribution calculating device for performing an operation of a three-dimensional concentration distribution of radioactive material.

  According to the gamma camera disclosed in the present application, gamma ray incident direction information and energy information, physical property information of the measurement target, and, based on the measurement condition information of the radiation detector, based on the energy change of gamma rays scattered inside the measurement target. By calculating the direction change and limiting the distribution area of radioactive materials, even if high-density materials that scatter most of the gamma rays inside the object are to be measured, the three-dimensional concentration distribution of radioactive materials can be shortened. It is possible to measure with high sensitivity over time.

FIG. 2 is a configuration diagram of a gamma camera according to Embodiment 1. FIG. 4 is a diagram illustrating a method for measuring a three-dimensional concentration distribution of a radioactive substance by the gamma camera according to the first embodiment. FIG. 2 is a hardware configuration diagram of a three-dimensional distribution calculation device in the gamma camera according to Embodiment 1. It is a figure explaining the energy distribution of the direct component of a gamma ray from a radioactive material, and a scattering component. FIG. 5 is a diagram illustrating a probability distribution of a difference between a scattering probability and an absorption probability of a gamma ray inside a measurement target. FIG. 3 is a diagram illustrating a flow of processing in the three-dimensional distribution calculation device of the gamma camera according to Embodiment 1. FIG. 4 is a diagram illustrating a method for estimating a three-dimensional concentration distribution of a radioactive substance in the gamma camera according to the first embodiment. FIG. 9 is a configuration diagram of a gamma camera according to Embodiment 2. FIG. 11 is a diagram for explaining a processing flow in the three-dimensional distribution calculation device of the gamma camera according to the second embodiment.

Embodiment 1 FIG.
Hereinafter, the gamma camera according to the first embodiment will be described with reference to the drawings. FIG. 1 is a configuration diagram of a gamma camera according to Embodiment 1, FIG. 2 is a diagram illustrating a method of measuring a three-dimensional concentration distribution of a radioactive substance by the gamma camera according to Embodiment 1, and FIG. FIG. 3 is a hardware configuration diagram of a three-dimensional distribution calculation device in the gamma camera according to Embodiment 1. In each of the drawings, the same or corresponding parts have the same reference characters allotted.

  The measurement target of the gamma camera 100 according to the first embodiment is mainly a substance having a higher density than a human body, such as concrete, metal, and the like. The radioactive material present in the measurement object contains radionuclides that emit radiation and decay to be converted into other nuclei. Gamma rays (hereinafter referred to as γ-rays) are emitted from γ-ray nuclides. As shown in FIG. 2, γ-rays coming from a radioactive substance 11 present inside the measurement target 10 are divided into a direct component 12 directly incident on the gamma camera 100 and a scattered component 13 scattered inside the measurement target 10. Divided. When the measurement target 10 is a high-density substance, most of the γ-rays are scattered inside the measurement target.

  As shown in FIG. 1, the gamma camera 100 includes a radiation detector 1, a gamma ray data storage unit 2 (hereinafter, referred to as a gamma ray data storage unit 2), a physical property information acquisition device 3, a physical property information storage unit 4, and a measurement condition acquisition. The apparatus includes a device 5, a measurement condition storage unit 6, a three-dimensional distribution calculation device 7, and a display unit 8. The radiation detector 1 measures the incident direction and energy of γ-rays coming from the radioactive substance 11 existing in the measurement target. At this time, the γ-ray detected by the radiation detector 1 includes both the direct component 12 and the scatter component 13.

  The radiation detector 1 has a γ-ray sensor that outputs a voltage or current intensity determined according to the position where the γ-ray has reacted due to the incidence of the γ-ray. A gamma ray sensor includes a plurality of semiconductor detectors, a plurality of electrodes for extracting signals from the semiconductor detector, a scintillator for converting gamma rays into ultraviolet light, visible light, and infrared light, and light detection. A unit in which a plurality of units including a unit are arranged is used.

  As the semiconductor detector, a detector using Si, CdTe, CdZnTe, or the like is used. In the case of a semiconductor detector, the position where the γ-ray has reacted is detected from the position where the semiconductor detector to which the γ-ray has reacted or the position of the electrode from which the signal has been extracted. On the other hand, the scintillator includes a scintillation material such as NaI (Tl), CsI (Tl), BGO, LSO, and the like, and the light from the scintillator is detected by a light detection unit. In the case of a scintillator, the position where the γ-ray has reacted is detected from the position where light from the scintillation material is detected.

  Further, the radiation detector 1 has a configuration for specifying the incident direction of the γ-ray. For example, a configuration combining a γ-ray sensor and a housing having one or more holes in a shielding body that blocks γ-rays, or a configuration combining a γ-ray sensor and a collimator that limits the incident direction of γ-rays Or a configuration in which two or more γ-ray sensors are arranged. The γ-ray data storage unit 2 includes a detected energy storage unit 21 and an incident direction storage unit 22, and stores energy information and incident direction information of γ-rays detected by the radiation detector 1, respectively.

  The physical property information acquisition device 3 measures the density, the density distribution, the components (constituent elements), the mixing ratio of the constituent elements, the thickness, and the like of the measurement target as the physical property information of the measurement target. The physical property information acquired by the physical property information acquiring device 3 includes at least a component to be measured and a density. The physical property information acquiring device 3 includes a plurality of devices selected from an X-ray inspection device, a γ-ray inspection device, a neutron inspection device, an ultrasonic inspection device, and an ultrasonic inspection device. In addition, it is also possible to use apparatuses other than the above.

  The constituent elements to be measured and the mixing ratio are measured by an X-ray inspection device or a γ-ray inspection device. The density and density distribution of the measurement target are measured by a neutron beam inspection device, and the thickness dimension of the measurement object is measured by an ultrasonic inspection device or an ultrasonic inspection device. The physical property information storage unit 4 stores the physical property information acquired by the physical property information acquiring device 3. The measurement of the physical property information by the physical property information acquisition device 3 does not need to be performed at the same time as the measurement of the three-dimensional concentration distribution of the radioactive substance, and a part of the measurement target is collected in advance and the physical property information is measured. It is also possible to record it in the storage unit 4.

  The measurement condition acquisition device 5 acquires measurement condition information of the radiation detector 1. The measurement condition information includes the distance between the radiation detector 1 and the measurement target, and the viewing angle of the radiation detector 1. The measurement condition acquisition device 5 includes any one of a laser range finder, a radio range finder, an ultrasonic range finder, and a tape measure. However, it is also possible to use a device other than the above. The measurement condition storage unit 6 stores the measurement condition information acquired by the measurement condition acquisition device 5.

  The three-dimensional distribution calculation device 7 acquires the γ-ray data stored in the γ-ray data storage unit 2, the physical property information stored in the physical property information storage unit 4, and the measurement condition information stored in the measurement condition storage unit 6. Based on them, the energy change and direction change of the γ-ray scattered inside the measurement object are calculated, and the three-dimensional concentration distribution of the radioactive material is calculated. Specifically, the radiation energy emitted from the radionuclide estimated based on the physical property information of the measurement target is calculated, and the γ-ray is calculated based on the calculated radiation energy and the energy information acquired from the detected energy storage unit 21. Calculate the energy change of

  Further, the angle θ at which the γ-rays are scattered inside the measurement target is calculated from the energy change of the γ-rays scattered inside the measurement target, and the calculated angle θ and the incident direction information acquired from the incident direction storage unit 22 are calculated. Based on this, the distribution area of the radioactive material is limited. Further, the scattering position of the γ-ray inside the measurement target is estimated based on the physical property information of the measurement target, and the distribution region of the radioactive substance is further limited by weighting based on the estimated scattering position. As one of the calculation methods at this time, it is possible to apply the ML-EM method, the maximum entropy method, or the like that estimates the three-dimensional concentration distribution of the radioactive substance so that the distribution becomes the most reliable.

  The above calculation processing by the three-dimensional distribution calculation device 7 is performed on one γ-ray detected by the γ-ray sensor of the radiation detector 1. When the radiation detector 1 detects a plurality of γ-rays, the three-dimensional distribution calculation device 7 estimates the distribution area of the radioactive substance based on the incident direction information and the energy information of each of the plurality of γ-rays, and further estimates the plurality of γ-rays. A portion where the distribution regions overlap each other is defined as a radioactive material distribution region. The calculation result by the three-dimensional distribution calculation device 7 is displayed on the display unit 8.

  Note that the three-dimensional distribution calculation device 7 has a processing circuit 70 including a processor 71 and a memory 72 shown in FIG. The memory 72 includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Further, an auxiliary storage device of a hard disk may be provided instead of the flash memory. The processor 71 executes a program input from the memory 72. In this case, a program is input from the auxiliary storage device to the processor 71 via the volatile storage device.

  Next, a calculation method by the three-dimensional distribution calculation device 7 will be described in detail. Γ-rays emitted from radioactive materials undergo energy changes and direction changes due to scattering. The three-dimensional distribution calculation device 7 calculates an energy change and a direction change due to γ-ray scattering, and limits the distribution region of the radioactive substance based on the calculation result.

  FIG. 4 shows an energy distribution of a direct component and a scattering component of γ-rays from a radioactive substance. In FIG. 4, the vertical axis represents the count number and the horizontal axis represents the energy. The solid line A indicates the energy distribution of the direct component, and the dotted line B indicates the energy distribution of the scattered component. As shown in FIG. 4, the direct component of the γ-ray has a predetermined energy, but the energy of the scattered component is smaller and not constant than the energy of the direct component. From such a difference in energy distribution, it can be determined whether the γ-ray detected by the radiation detector 1 is a direct component or a scattered component.

  The three-dimensional distribution calculation device 7 calculates the probability p that γ-rays are scattered for each location inside the measurement target based on the physical property information stored in the physical property information storage unit 4. Generally used as a method for calculating the probability p is the density ρ of the measurement target, the distance L that the γ-ray has traveled inside the measurement target, and the scattering cross-section σ at which the elements constituting the measurement target scatter the γ-ray. This is a function of Equation 1.

  p = 1−exp (−ρσL) (Equation 1)

When the measurement object is composed of an aggregate of a plurality of elements, the density ρ _i of the aggregate of each element, the distance L _i that the γ-ray has traveled through the aggregate of each element, and the scattering cross section σ _The probability p that is scattered for each location inside the measurement target is calculated by the following Expression 2 based on _i .

p = 1−exp (Σ _i (−ρ _i σ _i L _i )) (Equation 2)

  Note that the method of calculating the probability p that γ rays are scattered is not limited to the above method using Expressions 1 and 2. As another calculation method, the physical property information of the measurement target acquired by the physical property information acquisition device 3 is used, a simulation is performed under conditions in which the physical property information of the measurement target is reproduced by random number calculation, and the probability p that γ rays are scattered is calculated. There is a way.

  Similarly, it is possible to calculate the probability that γ-rays are absorbed at each location inside the measurement target based on the physical property information obtained from the physical property information storage unit 4 by the above method using Equations 1 and 2. It is. In that case, the cross-sectional area where the element constituting the measurement object absorbs γ-rays is applied to Equations 1 and 2. Similarly, the simulation of calculating the probability p that γ rays are scattered can also calculate the probability that γ rays are absorbed.

  FIG. 5 shows the scattering probability and the absorption probability of γ-rays inside the measurement object. Here, the scattering probability is the probability that gamma rays emitted from the radioactive substance inside the measurement target are scattered inside the measurement target, and the absorption probability is the gamma ray emitted from the radioactive substance inside the measurement target. This is the probability of being absorbed inside the measurement target. In FIG. 5, the vertical axis represents the probability, the horizontal axis represents the distance (L) traveled by the radiation (γ-ray) inside the measurement object, the solid line S represents the scattering probability, the dotted line A represents the absorption probability, and the dashed line D represents the scattering probability. The difference in absorption probability is shown.

  As shown in FIG. 5, when the distance traveled by the γ-rays in the measurement target increases, the γ-rays are scattered by 100%, and when the distance further increases, the γ-rays are absorbed by 100%. For this reason, if the distance traveled by the γ-rays within the measurement target increases, both the scattering probability and the absorption probability become 1. If γ-rays are absorbed 100% inside the measurement target, the radiation detector 1 cannot detect γ-rays.

  At a certain location inside the measurement target, the probability that the γ-ray is scattered at that location has a probability distribution like the difference between the scattering probability and the absorption probability (indicated by D in FIG. 4). Therefore, the position information of the location where the γ-rays are scattered inside the measurement target can be estimated using the probability distribution of the difference between the scattering probability and the absorption probability. When the measurement object is composed of an aggregate of a plurality of elements, the probability distribution of the difference between the scattering probability and the absorption probability corresponding to each element is used. The position information estimated by the probability distribution of the difference between the scattering probability and the absorption probability is used for weighting for limiting the distribution region of the radioactive material.

When γ rays are scattered inside the measurement object, energy loss of γ rays occurs due to Compton scattering, and the energy E ′ of the γ rays after the energy loss becomes the energy E before being scattered and the static energy of electrons. The energy E ₀ and the scattered angle θ are represented by the following Equation 3. In Equation 3, E is the energy of the γ-ray before being scattered, E ′ is the energy of the γ-ray after the energy loss due to Compton scattering, and θ is the angle at which the γ-ray emitted from the radioactive material is scattered inside the measurement object. It is.

E ′ = E / (1 + E × (1−cos θ) / E ₀ ) (Equation 3)

  In Equation 3, the energy E before being scattered is obtained from the radiation energy emitted from the γ-ray nuclide estimated from the physical property information of the measurement target. The energy E ′ of the γ-ray after the energy loss is the energy of the γ-ray detected by the radiation detector 1 and is stored in the detected energy storage unit 21 as energy information. The angle θ at which the γ-rays emitted from the radioactive substance are scattered inside the measurement target is obtained from the equation (3).

  The flow of processing in the three-dimensional distribution calculation device 7 of the gamma camera 100 according to Embodiment 1 will be described with reference to the flowchart in FIG. First, in step S <b> 1, energy information of γ-rays detected by the radiation detector 1 is obtained from the detected energy storage unit 21. Subsequently, in step S2, a radionuclide (γ-ray nuclide) existing in the measurement target is estimated based on the physical property information of the measurement target acquired from the physical property information storage unit 4. Further, in step S3, the radiation energy emitted from the estimated γ-ray nuclide is calculated.

  Subsequently, in step S4, the γ-rays emitted from the radioactive material are scattered inside the measurement object using the γ-ray energy information obtained in step S1 and the radiation energy emitted from the estimated γ-ray nuclide calculated in step S3. The calculated angle θ is calculated by the above-described method. Next, in step S5, the incident direction information of one γ ray detected by the radiation detector 1 is acquired from the incident direction storage unit 22.

  Further, in step S6, an operation for limiting the distribution region of the radioactive material is performed using the angle θ calculated in step S4 and the γ-ray incident direction information obtained in step S5. The distribution region of the radioactive substance obtained from the angle θ calculated by Expression 3 and the incident direction information of the γ-ray acquired by the radiation detector 1 has a conical shape. That is, in step S6, the distribution region of the radioactive substance is limited to the region inside the cone.

  Subsequently, in steps S7 and S8, based on the physical property information of the measurement object acquired from the physical property information storage unit 4, the scattering probability and the absorption probability of γ-rays are calculated by the methods described above. Finally, in step S9, the distribution area of the radioactive substance defined in step S6 is weighted by the scattering probability and the absorption probability calculated in steps S7 and S8 by the above-described method, and the distribution area of the radioactive substance is further limited. I do.

  In the flowchart of FIG. 6, the order of the processes from step S1 to step S9 can be changed as appropriate. The processing of steps S1 to S5 may be performed before the processing of step S6, and the processing of step S1 may be performed after the processing of steps S2 and S3. Similarly, the processing in steps S7 and S8 may be performed before the processing in step S9.

  The processing from step S1 to step S9 is performed for one γ-ray detected by the γ-ray sensor of the radiation detector 1. When the γ-ray sensor detects two or more γ-rays, it becomes possible to superimpose the three-dimensional concentration distribution of the radioactive substance calculated by each γ-ray. A method of estimating the three-dimensional concentration distribution of a radioactive substance when the gamma camera 100 detects a plurality of γ-rays will be described with reference to FIG. FIG. 7A shows a state in which the gamma camera and the object to be measured are arranged in a direction perpendicular to the paper surface, and FIG. 7B shows a state in which the gamma camera and the object to be measured are arranged in parallel to the paper surface. ing.

  7A and 7B, the two-dot chain line T1 is the locus of the first γ-ray detected by the gamma camera 100, and the one-dot chain line T2 is the second γ detected by the gamma camera 100. A1 indicates the distribution area of the radioactive substance estimated from the first γ-ray, A2 indicates the distribution area of the radioactive substance estimated from the second γ-ray, and A3 indicates the two γ-rays. 3 shows the distribution region of the radioactive material estimated from.

  The three-dimensional distribution calculation device 7 limits the distribution region of the radioactive material based on the calculation results of the first γ-ray energy change and direction change (step S6 in FIG. 6), and further weights the scattering probability and the absorption probability. (Step S9 in FIG. 6) to estimate the distribution region A1 of the radioactive material. Similarly, the distribution area A2 is estimated by the second γ-ray, and the distribution area A3 of the radioactive substance is estimated by superimposing these distribution areas A1 and A2. In the region where the radioactive substance is truly present, the overlapping of the distribution regions of the radioactive substance calculated from the respective γ-rays increases. In other words, the greater the overlap, the higher the probability of being a true radioactive substance distribution area, and the more accurate the measurement of the three-dimensional concentration distribution.

  As described above, according to the gamma camera 100 according to the first embodiment, based on the incident direction information and energy information of the γ-ray, the physical property information of the measurement target, and the measurement condition information of the radiation detector 1, the inside of the measurement target Calculates the energy change and direction change of γ-rays scattered in the above, so that the distribution area of the radioactive material is limited, so when the high-density material where most γ-rays are scattered inside the object is the measurement target Also, it is possible to measure the three-dimensional concentration distribution of the radioactive substance in a short time with high sensitivity.

  In addition, the distribution area of the radioactive substance is further limited by weighting based on the scattering probability and the absorption probability calculated based on the physical property information of the measurement object, so that the measurement accuracy is improved. When a plurality of γ-rays are detected, the measurement accuracy is further improved by overlapping the distribution regions of the radioactive substances estimated from the respective γ-rays.

Embodiment 2 FIG.
FIG. 8 shows a configuration diagram of the gamma camera according to the second embodiment. The gamma camera 100A according to the second embodiment stores, in the gamma camera 100 according to the first embodiment, a shape information acquisition device 14 that acquires a shape of a measurement target and shape information acquired by the shape information acquisition device 14. And a shape information storage unit 15 to be added. As the shape information acquisition device 14, a three-dimensional shape measurement device, a contour shape measurement device, or the like is used. The other configuration is the same as that of the first embodiment, and the description is omitted here.

  The gamma camera 100 according to Embodiment 1 performs the calculation including γ-rays from a region other than the measurement target. On the other hand, the three-dimensional distribution calculation device 7A of the gamma camera 100A according to the second embodiment can correct the distribution region of the radioactive material based on the shape information of the measurement target acquired from the shape information storage unit 15. . Specifically, the distribution region of the radioactive substance obtained by the calculation is compared with the shape information of the measurement target acquired by the shape information acquisition device 14, and the result of the calculation for the region other than the measurement target is removed.

  The flow of processing in the three-dimensional distribution calculation device 7A of the gamma camera 100A according to Embodiment 2 will be described with reference to the flowchart in FIG. Note that the processing from step S11 to step S18 in FIG. 9 is the same as the processing from step S1 to step S8 in the flowchart in FIG. 6 described in the first embodiment, and a description thereof will not be repeated. In step S19 of FIG. 9, the γ in the measurement target is determined based on the incident direction information of the γ-ray acquired in step S15, the scattering probability of the γ-ray calculated in step S17, and the absorption probability of the γ-ray calculated in step S18. Estimate the scattering position of the line.

  Subsequently, in step S20, the distribution area of the radioactive material defined in step S16 is weighted by the γ-ray scattering position estimated in step S19 in the same manner as in the first embodiment, and the distribution area of the radioactive substance is determined. Is further limited. Next, in step S21, the shape information of the measurement target stored in the shape information storage unit 15 is obtained. Finally, in step S22, the shape information of the measurement target acquired in step S21 is compared with the distribution region of the radioactive substance defined in step S20, and the distribution region is corrected.

  Note that the order of the processes from step S11 to step S22 can be changed as appropriate. The processing of steps S11 to S15 may be performed before the processing of step S16, and the processing of step S11 may be performed after the processing of steps S12 and S13. Further, the shape information acquisition processing in step S21 may be performed before the processing in step S16, and the calculation of the three-dimensional concentration distribution of the radioactive substance in the region other than the measurement target may not be performed.

  According to the second embodiment, in addition to the same effects as in the first embodiment, the distribution region of the radioactive substance obtained by the calculation is compared with the shape information of the measurement object acquired by the shape information acquiring device 14 to obtain the distribution. Since the correction of the region is performed, the calculation result for the region other than the measurement target can be removed, and the measurement accuracy is improved. Further, since the calculation of the three-dimensional concentration distribution of the radioactive substance in the region other than the measurement target can be prevented from being performed, the time required for the calculation can be reduced as compared with the first embodiment.

  Although this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments may differ from those of the specific embodiments. The present invention is not limited to the application, and can be applied to the embodiment alone or in various combinations. Accordingly, innumerable modifications not illustrated are contemplated within the scope of the technology disclosed herein. For example, a case where at least one component is deformed, added or omitted, and a case where at least one component is extracted and combined with a component of another embodiment are included.

  The present application can be used as a gamma camera for measuring a three-dimensional concentration distribution of a radioactive substance.

  Reference Signs List 1 radiation detector, 2 gamma ray data storage unit, 3 physical property information acquisition device, 4 physical property information storage unit, 5 measurement condition acquisition device, 6 measurement condition storage unit, 7, 7A three-dimensional distribution calculation device, 8 display unit, 10 measurement Object, 11 radioactive material, 12 direct component, 13 scattering component, 14 shape information acquisition device, 15 shape information storage unit, 21 detected energy storage unit, 22 incident direction storage unit, 70 processing circuit, 71 processor, 72 memory, 100, 100A gamma camera

Claims (11)

A radiation detector for detecting the incident direction and energy of gamma rays coming from the measurement object,
A gamma ray data storage unit for storing incident direction information and energy information obtained by the radiation detector,
Physical property information acquisition device that acquires physical property information including at least the component and density of the measurement target,
Physical property information storage unit that stores the physical property information of the measurement target acquired by the physical property information acquisition device,
A measurement condition acquisition device for acquiring measurement condition information of the radiation detector,
A measurement condition storage unit that stores measurement condition information acquired by the measurement condition acquisition device,
Based on the incident direction information and energy information stored in the gamma ray data storage unit, the physical property information stored in the physical property information storage unit, and the scattering inside the measurement target based on the measurement condition information stored in the measurement condition storage unit. A gamma camera comprising a three-dimensional distribution calculation device for calculating a change in energy and a change in direction of the gamma ray and calculating a three-dimensional concentration distribution of the radioactive material.   The gamma camera according to claim 1, further comprising: a shape information acquisition device that acquires shape information of a measurement target; and a shape information storage unit that stores shape information acquired by the shape information acquisition device.   The gamma camera according to claim 2, wherein the three-dimensional distribution calculation device corrects a distribution region of the radioactive material based on shape information of the measurement target acquired from the shape information storage unit.   4. The physical property information acquisition device according to claim 1, wherein the physical property information of the measurement target acquires a density distribution, a mixing ratio of constituent elements, and a thickness dimension of the measurement target. The gamma camera according to the above.   The said physical-property information acquisition apparatus contains several apparatuses selected from the X-ray inspection apparatus, the gamma-ray inspection apparatus, the neutron beam inspection apparatus, the ultrasonic inspection apparatus, and the sonic inspection apparatus. The gamma camera according to any one of the above.   6. The measurement condition acquisition apparatus according to claim 1, wherein the measurement condition information acquires a distance between the radiation detector and a measurement target and a viewing angle of the radiation detector as measurement condition information. The gamma camera according to the item.   The gamma camera according to any one of claims 1 to 6, wherein the measurement condition acquisition device includes one of a laser range finder, a radio range finder, an ultrasonic range finder, and a tape measure.   The three-dimensional distribution calculation device calculates the radiation energy emitted from the radionuclide estimated based on the physical property information of the measurement target, and calculates the gamma ray based on the calculated radiation energy and the energy information obtained from the gamma ray data storage unit. The gamma camera according to any one of claims 1 to 7, wherein an energy change of the gamma camera is calculated.   The three-dimensional distribution calculation device calculates the angle at which gamma rays are scattered inside the measurement target from the energy change of the gamma rays scattered inside the measurement target, and calculates the calculated angle and the incident direction information obtained from the gamma ray data storage unit. The gamma camera according to any one of claims 1 to 8, wherein a distribution region of the radioactive substance is limited on the basis of:   The three-dimensional distribution calculation device estimates a gamma ray scattering position inside the measurement target based on physical property information of the measurement target, and limits a distribution region of the radioactive material by weighting with the estimated scattering position. The gamma camera according to any one of claims 1 to 9.   When the radiation detector detects the incident direction and energy of a plurality of gamma rays, the three-dimensional distribution calculation device estimates the distribution area of the radioactive material based on the incident direction information and the energy information of each of the plurality of gamma rays, and estimates The gamma camera according to any one of claims 1 to 10, wherein a portion where the plurality of distribution regions overlap each other is defined as a distribution region of a radioactive substance.

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