JP6983129B2 - Gamma camera - Google Patents

Description

The present application relates to a gamma camera that measures a three-dimensional concentration distribution of radioactive substances.

Conventionally, a gamma camera has been used to measure the concentration distribution of radioactive substances, 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 Document 1, one gamma camera is used to capture two images on an imaging axis tilted at the same angle to the left and right from a vertical line with respect to the front surface of the measurement target, and a stereoscopic image is obtained from the two obtained images. Is getting.

Further, as a method of imaging a 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, focusing on the phenomenon that gamma rays from a gamma ray source are scattered by the pre-stage detector and then photoelectrically absorbed by the post-stage detector, and each detection is performed. The three-dimensional distribution of the gamma ray source is imaged based on the detection position and the detection energy of the gamma ray in the detector.

As a measurement method using this Compton camera, for example, in Patent Document 2, a radiation measuring device provided with two detection units arranged in front and behind when viewed from the radiation generation side, the position of a scattering point, the position of an absorption point, and the radiation energy are used. Therefore, the position of the radiation source is specified as a conical surface (Compton cone) whose apex is the scattering point.

Further, Patent Document 3 describes an image based on the maximum likelihood estimation expected value maximization method (ML-EM method), which is a statistical method, as a method for optimizing the three-dimensional distribution image of a gamma ray source by a Compton camera. The reconstruction method is shown. Further, Non-Patent Document 1 describes a list mode maximum likelihood reconstruction method (LM-ML-EM method) of a Compton scattering camera image in nuclear medicine. According to the LM-ML-EM method, even if it is difficult to obtain the gamma ray source distribution in space from the 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.

Japanese Unexamined Patent Publication No. 9-218268 Japanese Unexamined Patent Publication No. 2011-85418 WO2016-035706 Gazette

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

In a conventional gamma camera, in order to measure the three-dimensional concentration distribution of a radioactive substance, only the gamma rays directly incident from the radioactive substance are used as data, and the gamma rays scattered between the radioactive substance and the radiation detector are detected. Is not used as data. On the other hand, when the measurement target is a substance having a higher density than that of 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 a radioactive substance when the measurement target is a high-density substance.

As a method of measuring the three-dimensional concentration distribution of a radioactive substance in a measurement target, in a method of moving one gamma camera to perform multiple measurements as in Patent Document 1, the gamma camera is connected to a drive unit and moved. There is a problem that the measurement time becomes long because a mechanism for making the measurement is required and the measurement is performed a plurality of times. Further, in the methods of Patent Document 2, Patent Document 3, and Non-Patent Document 1, the three-dimensional concentration distribution of the radioactive substance is measured by one measurement with one gamma camera, but the measurement using Compton scattering is used. The method, a method that applies only to so-called Compton cameras.

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

The gamma camera disclosed in the present application includes a radiation detector that detects the incident direction and energy of gamma rays coming from a measurement target, a gamma ray data storage unit that stores incident direction information and energy information acquired by the radiation detector, and a gamma ray data storage unit. A physical property information acquisition device that acquires physical property information including at least the components and densities 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 energy information stored in the gamma ray data storage unit, and the physical property information storage unit are stored. Based on the physical property information and the measurement condition information stored in the measurement condition storage unit, the energy change and direction change of the gamma rays scattered inside the measurement target are calculated, and the three-dimensional concentration distribution of the radioactive substance is calculated. It is equipped with an elemental distribution calculation device.

According to the gamma camera disclosed in the present application, the energy change of the gamma ray scattered inside the measurement target is based on the incident direction information and energy information of the gamma ray, the physical property information of the measurement target, and the measurement condition information of the radiation detector. Since the direction change is calculated and the distribution area of the radioactive substance is limited, the three-dimensional concentration distribution of the radioactive substance is shortened even when the measurement target is a high-density substance in which most of the gamma rays are scattered inside the object. It is possible to measure with high sensitivity in time.

It is a block diagram of the gamma camera which concerns on Embodiment 1. FIG. It is a figure explaining the method of measuring the three-dimensional concentration distribution of a radioactive substance by the gamma camera which concerns on Embodiment 1. FIG. It is a hardware block diagram of the 3D distribution arithmetic unit in the gamma camera which concerns on Embodiment 1. FIG. It is a figure explaining the energy distribution of the direct component and the scattering component of the gamma ray from a radioactive substance. It is a figure explaining the probability distribution of the difference between the scattering probability and the absorption probability of gamma rays in the measurement target. It is a figure explaining the flow of processing in the 3D distribution arithmetic unit of the gamma camera which concerns on Embodiment 1. FIG. It is a figure explaining the method of estimating the three-dimensional concentration distribution of a radioactive substance in the gamma camera which concerns on Embodiment 1. FIG. It is a block diagram of the gamma camera which concerns on Embodiment 2. FIG. It is a figure explaining the flow of processing in the 3D distribution arithmetic unit of the gamma camera which concerns on Embodiment 2. FIG.

Embodiment 1.
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 the first embodiment, 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 the first embodiment, and FIG. 3 is an embodiment. It is a hardware block diagram of the 3D distribution arithmetic unit in the gamma camera which concerns on Embodiment 1. FIG. In each figure, the same and corresponding parts are designated by the same reference numerals.

The measurement target of the gamma camera 100 according to the first embodiment is mainly a substance having a higher density than that of the human body, for example, concrete, metal, or the like. The radioactive material present in the measurement target contains radionuclides that emit radiation and decay to change into other nuclei. Gamma rays (hereinafter referred to as γ rays) are emitted from gamma ray nuclides. As shown in FIG. 2, the γ-rays coming from the radioactive substance 11 existing inside the measurement target 10 are directed to the direct component 12 directly incident on the gamma camera 100 and the 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 measurement condition acquisition. It 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 the 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 scattering component 13.

The radiation detector 1 has a γ-ray sensor that outputs a voltage or current intensity determined by energy and a position where the γ-ray reacts due to the incident of the γ-ray. Gamma-ray sensors include those with multiple semiconductor detectors, those with multiple electrodes that extract signals from semiconductor detectors, and scintillators and photodetectors that convert γ-rays into ultraviolet light, visible light, and infrared light. A unit in which a plurality of units including a unit are arranged is used.

As the semiconductor type 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 reacts is detected from the position where the semiconductor detector with which the γ-ray reacts is arranged or the position of the electrode from which the signal is taken out. On the other hand, the scintillator contains a scintillation material such as NaI (Tl), CsI (Tl), BGO, LSO, etc., and the light from the scintillator is detected by the photodetector. In the case of a scintillator, the position where the γ-ray reacts is detected from the position where the 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 in which a γ-ray sensor is combined with a housing having one or more holes in a shield that shields γ-rays, or a configuration in which a γ-ray sensor and a collimeter that limits the incident direction of γ-rays are combined. , Or a configuration in which two or more γ-ray sensors are arranged side by side corresponds to this. The γ-ray data storage unit 2 has a detection energy storage unit 21 and an incident direction storage unit 22, and stores γ-ray energy information and incident direction information detected by the radiation detector 1, respectively.

The physical property information acquisition device 3 measures the density, density distribution, component (constituent element), mixing ratio of the constituent elements, thickness dimension, etc. of the measurement target as the physical property information of the measurement target. The physical property information acquired by the physical property information acquisition device 3 includes at least the components and densities to be measured. The physical property information acquisition device 3 includes a plurality of devices selected from an X-ray inspection device, a γ-ray inspection device, a neutron beam inspection device, an ultrasonic inspection device, and a sound wave inspection device. It is also possible to use a device 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 target is measured by an ultrasonic inspection device or a sound wave inspection device. The physical property information storage unit 4 stores the physical property information acquired by the physical property information acquisition device 3. The measurement of the physical property information by the physical property information acquisition device 3 does not have to be performed at the same time as the measurement of the three-dimensional concentration distribution of the radioactive substance. It is also possible to record in the storage unit 4.

The measurement condition acquisition device 5 acquires the 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 wave 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 these, the energy change and direction change of the γ-rays scattered inside the measurement target are calculated, and the three-dimensional concentration distribution of the radioactive substance is calculated. Specifically, the radiation energy emitted from the radioactive nuclei estimated based on the physical property information of the measurement target is calculated, and the γ-ray is 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 in 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 used. Based on this, the distribution area of radioactive substances is limited. In addition, the scattering position of γ-rays 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 according to the estimated scattering position. As one of the calculation methods at this time, it is possible to apply the ML-EM method or the maximum entropy method for estimating the three-dimensional concentration distribution of the radioactive substance so that the distribution is most reliable.

The above arithmetic processing by the three-dimensional distribution arithmetic unit 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 region 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. The part where the distribution areas of the above overlap is defined as the distribution area of radioactive substances. The calculation result by the three-dimensional distribution calculation device 7 is displayed on the display unit 8.

The three-dimensional distribution arithmetic unit 7 has a processing circuit 70 including the processor 71 and the 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, the auxiliary storage device of the hard disk may be provided instead of the flash memory. The processor 71 executes the 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, the calculation method by the three-dimensional distribution calculation device 7 will be described in detail. Gamma rays emitted from radioactive materials cause energy changes and direction changes due to scattering. The three-dimensional distribution calculation device 7 calculates the energy change and the direction change due to the scattering of γ-rays, and limits the distribution area of the radioactive substance based on the calculation result.

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

The three-dimensional distribution calculation device 7 calculates the probability p that γ-rays are scattered at 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 in which the γ-ray travels inside the measurement target, and the scattering cross section σ in which the elements constituting the measurement target scatter the γ-ray. It is a function of Equation 1.

p = 1-exp (-ρσL) (Equation 1)

If the measurement object is composed of a set of a plurality of elements, the density [rho _i of a collection of the respective _elements, the distance γ rays advances the assembly of the respective elements L _i, and the scattering cross section σ _The probability p of being scattered at each location inside the measurement target is calculated by the following equation 2 according to i.

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

The method for calculating the probability p at which γ-rays are scattered is not limited to the above method using Equations 1 and 2. As another calculation method, using the physical property information of the measurement target acquired by the physical property information acquisition device 3, a simulation is performed under the condition that 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, by the above method using the formulas 1 and 2, 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 acquired from the physical property information storage unit 4. Is. In that case, the cross-sectional area in which the element constituting the measurement target absorbs γ-rays is applied to the formulas 1 and 2. Similarly, the probability that γ-rays are absorbed can also be calculated by a simulation that calculates the probability p that γ-rays are scattered.

FIG. 5 shows the scattering probability and the absorption probability of γ-rays inside the measurement target. Here, the scattering probability is the probability that γ-rays emitted from the radioactive substance inside the measurement target are scattered inside the measurement target, and the absorption probability is the γ-ray emitted from the radioactive material inside the measurement target. It is the probability of being absorbed inside the measurement target. In FIG. 5, the vertical axis is the probability, the horizontal axis is the distance (L) that the radiation (γ ray) has traveled inside the measurement target, the solid line S is the scattering probability, the dotted line A is the absorption probability, and the alternate long and short dash line D is the scattering probability. The difference in absorption probability is shown respectively.

As shown in FIG. 5, when the distance traveled by the γ-rays is long inside the measurement target, 100% of the γ-rays are scattered, and when the distance is further long, 100% of the γ-rays are absorbed. Therefore, when the distance traveled by the γ-rays becomes long inside the measurement target, both the scattering probability and the absorption probability become 1. If 100% of the γ-rays are absorbed inside the measurement target, the radiation detector 1 cannot detect the γ-rays.

The probability that γ-rays are scattered at a certain place inside the measurement target has a probability distribution such as 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 by using the probability distribution of the difference between the scattering probability and the absorption probability. When the measurement target 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 to limit the distribution region of the radioactive material.

Further, when γ-rays are scattered inside the measurement target, energy loss of γ-rays occurs due to Compton scattering, and the energy E'of γ-rays after the energy loss is the energy E before being scattered and the electron stationary. It is represented by the following equation 3 by the energy E _{0 and the scattered angle θ.} In Equation 3, E is the energy of the γ-rays before being scattered, E'is the energy of the γ-rays after the energy loss due to Compton scattering, and θ is the angle at which the γ-rays emitted from the radioactive substance are scattered inside the measurement target. Is.

E'= E / (1 + E × (1-cosθ) / 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. Further, the γ-ray energy E'after the energy loss is the γ-ray energy detected by the radiation detector 1, and is stored in the detection energy storage unit 21 as energy information. From this equation 3, the angle θ at which the γ-rays emitted from the radioactive substance are scattered inside the measurement target can be obtained.

The flow of processing in the three-dimensional distribution calculation device 7 of the gamma camera 100 according to the first embodiment will be described with reference to the flowchart of FIG. First, in step S1, the energy information of the γ-rays detected by the radiation detector 1 is acquired from the detection energy storage unit 21. Subsequently, in step S2, the 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 target using the γ-ray energy information acquired 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 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 calculation for limiting the distribution region of the radioactive substance is performed using the angle θ calculated in step S4 and the incident direction information of the γ-rays acquired in step S5. The distribution region of the radioactive substance obtained from the angle θ calculated by the equation 3 and the incident direction information of the γ-rays 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 shape.

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

In the flowchart of FIG. 6, the order of processing 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 of step S7 and step S8 may be performed before the processing of step S9.

The processing of steps S1 to S9 is performed on 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 is 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 the radioactive substance when the gamma camera 100 detects a plurality of gamma rays will be described with reference to FIG. 7. FIG. 7A shows a state in which the gamma camera and the measurement target are arranged in the direction perpendicular to the paper surface, and FIG. 7B shows a state in which the gamma camera and the measurement target are arranged parallel to the paper surface. ing.

In FIGS. 7 (a) and 7 (b), the two-point chain line T1 is the locus of the first γ-ray detected by the gamma camera 100, and the one-point chain line T2 is the second γ detected by the gamma camera 100. The locus of the line is shown, A1 is the distribution area of the radioactive substance estimated from the first γ-ray, A2 is the distribution area of the radioactive substance estimated from the second γ-ray, and A3 is the distribution area of the two γ-rays. The distribution area of radioactive substances estimated from is shown.

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

As described above, according to the gamma camera 100 according to the first embodiment, the inside of the measurement target is 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. Since the energy change and direction change of the γ-rays scattered in the above are calculated and the distribution area of the radioactive material is limited, the measurement target is a high-density material in which most of the γ-rays are scattered inside the object. However, it is possible to measure the three-dimensional concentration distribution of radioactive substances in a short time with high sensitivity.

Further, since the distribution region of the radioactive substance is further limited by the weighting based on the scattering probability and the absorption probability calculated based on the physical property information of the measurement target, the measurement accuracy is improved. Further, when a plurality of γ-rays are detected, the measurement accuracy is further improved by superimposing the distribution regions of the radioactive substances estimated from the respective γ-rays.

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

The gamma camera 100 according to the first embodiment performs a 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 substance 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 calculation result 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 the second embodiment will be described with reference to the flowchart of FIG. Since the processes of steps S11 to S18 of FIG. 9 are the same as the processes of steps S1 to S8 of the flowchart of FIG. 6 described in the first embodiment, the description thereof will be omitted here. In step S19 of FIG. 9, γ inside the measurement target is based on the incident direction information of γ-rays acquired in step S15, the scattering probability of γ-rays calculated in step S17, and the absorption probability of γ-rays calculated in step S18. Estimate the scattering position of the line.

Subsequently, in step S20, the distribution region of the radioactive substance limited in step S16 is weighted by the scattering position of the γ-rays estimated in step S19 by the same method as in the first embodiment, and the distribution region of the radioactive substance is performed. Is further limited. Next, in step S21, the shape information of the measurement target stored in the shape information storage unit 15 is acquired. 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 limited in step S20, and the distribution region is corrected.

The order of processing 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 process in step S21 may be performed before the process in step S16 so that 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 effect as that of the first embodiment, the distribution region of the radioactive substance obtained by the calculation and the shape information of the measurement target acquired by the shape information acquisition device 14 are compared and distributed. Since the area is corrected, the result of calculation for the area 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, the time required for the calculation can be shortened as compared with the first embodiment.

The present disclosure describes various exemplary embodiments and examples, although the various features, embodiments, and functions described in one or more embodiments are those of a particular embodiment. It is not limited to application, but can be applied to embodiments alone or in various combinations. Therefore, innumerable variations not exemplified are envisioned within the scope of the techniques disclosed herein. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

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

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 Target, 11 radioactive material, 12 direct component, 13 scattered component, 14 shape information acquisition device, 15 shape information storage unit, 21 detection energy storage unit, 22 incident direction storage unit, 70 processing circuit, 71 processor, 72 memory, 100, 100A gamma camera

Claims (11)

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 incident direction information and energy information acquired by the radiation detector, and
A physical property information acquisition device that acquires physical property information including at least the components and densities to be measured,
A physical property information storage unit that stores physical property information of a measurement target acquired by the physical property information acquisition device, and a physical property information storage unit.
A measurement condition acquisition device that acquires measurement condition information of the radiation detector,
A measurement condition storage unit that stores measurement condition information acquired by the measurement condition acquisition device, and a measurement condition storage unit.
Scattered inside the measurement target 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 measurement condition information stored in the measurement condition storage unit. A gamma camera characterized by being equipped with a three-dimensional distribution calculation device that calculates the energy change and direction change of the gamma rays and calculates the three-dimensional concentration distribution of radioactive substances. The gamma camera according to claim 1, further comprising a shape information acquisition device for acquiring shape information of a measurement target and a shape information storage unit for storing the 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 a radioactive substance based on the shape information of a measurement target acquired from the shape information storage unit. One of claims 1 to 3, wherein the physical property information acquisition device acquires the density distribution of the measurement target, the mixing ratio of the constituent elements, and the thickness dimension as the physical property information of the measurement target. Gamma camera described in. Claims 1 to 4 are characterized in that the physical property information acquisition device includes a plurality of devices selected from an X-ray inspection device, a gamma ray inspection device, a neutron beam inspection device, an ultrasonic inspection device, and a sound wave inspection device. The gamma camera described in any one of the items. One of claims 1 to 5, wherein the measurement condition acquisition device acquires the distance between the radiation detector and the measurement target and the viewing angle of the radiation detector as measurement condition information. The gamma camera described in the section. The gamma camera according to any one of claims 1 to 6, wherein the measurement condition acquisition device includes any 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 radioactive nuclei estimated based on the physical property information of the measurement target, and gamma rays are based on the calculated radiation energy and the energy information acquired from the gamma ray data storage unit. The gamma camera according to any one of claims 1 to 7, wherein the energy change of the above 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 the calculated angle and the incident direction information acquired from the gamma ray data storage unit are used. The gamma camera according to any one of claims 1 to 8, wherein the distribution region of the radioactive substance is limited based on the above. The claim is characterized in that the three-dimensional distribution calculation device estimates the scattering position of gamma rays inside the measurement target based on the physical property information of the measurement target, and limits the distribution region of the radioactive substance by weighting by 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 and estimates the distribution region of the radioactive substance based on the incident direction information and energy information of each of the plurality of gamma rays. The gamma camera according to any one of claims 1 to 10, wherein the portion where the plurality of distribution regions overlap each other is used as the distribution region of the radioactive substance.

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