JP2017026423A - Compton camera, and displacement detection method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique of resolving a problem such as a case where there is deviation in relative positions among a plurality of Compton cameras and relative positions between Compton cameras and other imaging means.SOLUTION: A displacement detection method of a Compton camera that comprises an electron detector 1 having a scatterer, electron drifting means 12 and an electron collector 11, and a gamma-ray detector 2. Linear or planar first reference radiation flux is made incident to the scatterer, ionized electrons generated by interaction of the first reference radiation flux and the scatterer are moved to the electron collector by the drifting means, and displacement from a prescribed position of the electron detector is detected based on distribution of a first detection signal of ionized electrons detected by the electron collector.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Compton camera that acquires the incident direction of radiation (typically gamma rays) and displays, for example, its intensity distribution as an image, and a displacement detection method for the Compton camera.

  The following advanced Compton method is known as one of gamma ray detection methods. In this method, in addition to the scattered gamma ray energy and scattering direction vector generated by Compton scattering, the recoil electron energy generated by Compton scattering and the recoil direction vector at the Compton scattering point are used to determine the incident direction of the incident gamma ray. calculate. In addition, a Compton camera, which is a kind of gamma camera that can measure and image the intensity distribution of gamma rays emitted from a radiation source using this method, is known.

  Non-Patent Document 1 discloses a TPC (Time Projection Chamber) which is a detection device using such an advanced Compton method. The TPC is filled with a gas that is a scatterer, and a flat-plate electron collector (μPIC) that amplifies and detects ionized electrons is disposed. In addition, an electron drift region in which a uniform electric field is applied to the electron collector is formed in the TPC. In this electron drift region, incident gamma rays (photons) interact with electrons in gas molecules that are scatterers to cause Compton scattering. The recoil electrons generated as a result fly while ionizing gas molecules continuously, and an electron cloud composed of a large number of ionized electrons is generated on the tracks. This electron cloud drifts (moves) to the electron collector in the electron drift region while maintaining almost the same shape as the recoil electron track by the force received from the electric field. The electron collector is a two-dimensional electron detector, and detects the arrival position (X, Y coordinates) of the electron cloud (track) to the electron collector. The distance from the electron collector to the track from the difference between the time when the scattered gamma ray is detected by the scattered gamma ray detector, that is, the time when Compton scattering occurs and the time when the ion collector detects the ionized electrons, and the drift velocity of the ionized electrons. Z coordinate) is detected. In this way, the three-dimensional position of the recoil electron track can be acquired. In general, it is known that such a detector (TPC) can detect gamma rays in a wide energy range of about 1 keV to 2000 keV.

Kabuki S. et al., “Imaging Study of a phantom and Small animal with a two-head electron-tracking Compton gamma-ray camera”, Nuclear Science Symposium Conference Record (NSS / MIC 2010)

  When a three-dimensional distribution image of gamma ray intensity is obtained using a Compton camera, a plurality of Compton cameras arranged in different directions with respect to the inspection object are used. Then, the position information of the gamma rays obtained from each Compton camera is synthesized to obtain a three-dimensional distribution image. Further, in general, an intensity distribution image of gamma rays obtained by a Compton camera is displayed superimposed on a morphological image obtained by other imaging means, for example, an X-ray transmission image, and used for medical diagnosis or the like.

  Here, when there is a shift (displacement from the normal position) in the relative position between the plurality of Compton cameras or the relative position between the Compton camera and other imaging means, a correct three-dimensional distribution image is obtained. It may not be obtained. Alternatively, a deviation may occur between the superimposed gamma ray distribution image and the morphological image. For this reason, accurate diagnosis may be hindered.

  The displacement detection method according to the present invention is a displacement detection method for a Compton camera equipped with a scatterer, an electron drift means, an electron collector, and a gamma ray detector, and includes the following steps. A step of causing a linear or planar first reference radiation bundle to enter the scatterer. The step of moving ionized electrons generated by the interaction between the first reference radiation flux and the scatterer to the electron collector by the drift means. Detecting a displacement of the electron detector from a predetermined position based on a distribution of the first detection signal of the ionized electrons detected by the electron collector.

  A displacement correction method according to the present invention is a Compton camera arrangement correction method including an electron detector having a scatterer, an electron drift means, an electron collector, and a gamma ray detector, and is obtained by the displacement detection method described above. The arrangement of the electron detectors is corrected according to the displacement information.

  According to the displacement detection method of the present invention, it is possible to detect the displacement from the normal position of the electronic detector. Further, according to the arrangement correction method of the present invention, the arrangement of the electron detector can be corrected. By applying such a displacement detection method and arrangement correction method to a Compton camera, it is possible to correct a relative positional shift between a plurality of Compton cameras, and for example, a correct three-dimensional distribution image is obtained. In addition, the relative positional deviation between the Compton camera and other imaging means can be corrected. For example, the gamma ray distribution image and the morphological image can be accurately superimposed, and more accurate diagnosis can be performed. It becomes possible.

The figure which shows schematic structure of Embodiment 1 of a Compton camera. The figure explaining the detection principle of an electron detector and a scattering gamma ray detector. FIG. 3 is a diagram illustrating details of an electron detection circuit and a gamma ray detection circuit according to the first embodiment. The flowchart figure of the displacement detection and arrangement | positioning correction | amendment of the detector in Embodiment 1. FIG. FIG. 3 is a diagram illustrating the arrangement of a collimator and a reference radiation source in the first embodiment. FIG. 3 is a perspective view of a collimator according to the first embodiment. The perspective view which shows the proper arrangement | positioning state of an electron detector and a scattering gamma ray detector. The perspective view which shows the displacement state of an electron detector and a scattering gamma ray detector. The figure which looked at the electron detector without a displacement from the Y-axis direction. The histogram which shows the relationship between the detection position of an electronic lump and a count number in an electron detector without displacement. The figure which looked at the electronic detector with a displacement from the Y-axis direction. The histogram which shows the relationship between the detection position of an electronic lump and a count number in an electronic detector with displacement. The figure which looked at the scattering gamma ray detector with a displacement from the Y-axis direction. The histogram which shows the relationship between the detection position of a reference radiation, and a count number in the scattering gamma ray detector with a displacement. The figure which shows schematic structure of Embodiment 2 of a Compton camera. The figure which shows the flowchart of the displacement detection of the detector in Embodiment 2. FIG. FIG. 6 is a diagram for explaining the arrangement of a collimator and a reference radiation source in the second embodiment. The figure which shows the detail of the electronic detection circuit and gamma ray detection circuit in Embodiment 2. FIG. The figure which shows schematic structure of Embodiment 3 of a Compton camera. FIG. 6 is a diagram for explaining the arrangement of a collimator and a reference radiation source in a third embodiment. FIG. 6 is a perspective view of a collimator according to a third embodiment.

  According to the present invention, the displacement of the electron detector from a predetermined position is detected by detecting ionized electrons generated by Compton scattering instead of direct detection of radiation. The arrangement of the electron detectors can be corrected according to the information on the displacement.

(Embodiment 1)
FIG. 1 shows a schematic configuration of a first embodiment of a Compton camera to which a detector displacement detection method and a detector arrangement correction method according to the present invention are applied. Here, 1 is an electron detector, 2 is a scattered gamma ray detector or gamma ray detector, 3 is an adjustment mechanism, 4 is a signal processing device, 5 is a display device, 6 is a radiation source included in the inspection object, and 7 is an inspection. This is a holding unit for the object.

  The electron detector 1 includes a chamber 10 that is a container in which a gas (for example, argon, xenon, etc.) that is a scatterer is sealed, a plate-shaped electron collector 11 built in the chamber 10, and an electrode 12. The electron collector 11 and the electrode 12 face each other in parallel, and the electrode 12 is attached to the front end side (gamma ray incident side) of the chamber 10. By applying predetermined voltages to the electrode 12 and the electron collector 11 by the voltage generator 13, an electron drift region is formed between the electrode 12 and the electron collector 11. In this electron drift region, a uniform electric field acts in a direction perpendicular to the electron collector 11. In order to make the electric field in the electron drift region more uniform, a guide electrode (not shown) may be provided around the electron drift region. The electron detector 1 and the scattered gamma ray detector 2 constitute a TPC that is a three-dimensional position detector of electrons.

  The inspection object is, for example, a human body (subject), and the radiation source 6 in this case is the administered radiopharmaceutical. The radiation source 6 is made of a radioactive material that emits gamma rays having an energy of about 100 keV to 2000 keV. When inspecting an object, individual incident gamma rays (photons) that come from the radiation source 6 and pass through the front end of the chamber 10 and the electrode 12 and enter the electron drift region are converted into electrons in the gas molecules. Compton scattering is an interaction between the two. As a result, recoil electrons and scattered gamma rays are generated. The recoil electrons are detected by the electron collector 11 and the scattered gamma rays are detected by the scattered gamma ray detector 2.

  As shown in FIG. 1, the signal processing device 4 includes an electron detection circuit 20, a gamma ray detection circuit 21, a gamma ray incident direction calculation circuit 22 (hereinafter also simply referred to as a calculation circuit), and an image reconstruction device 23. The electron detection circuit 20 calculates the recoil electron energy, the Compton scattering point position, and the recoil direction vector from the recoil electron detection signal. The gamma ray detection circuit 21 calculates the energy of the scattered gamma ray and the scattering direction vector from the detection signal of the scattered gamma ray.

  The calculation circuit 22 calculates the incident direction of the incident gamma ray based on the energy of the recoil electron, the recoil direction vector, the energy of the scattered gamma ray, and the scattering direction vector for each Compton scattering event generated from the incident gamma ray (photon). calculate. The image reconstruction device 23 generates intensity distribution image data from information on the incident direction of incident gamma rays calculated for a plurality of Compton scattering events. The display device 5 uses this image data to display the intensity distribution of the radiation according to the density or the color difference.

  Next, the detection principle of the electron detector 1 and the scattered gamma ray detector 2 will be described with reference to FIG. In FIG. 2, the chamber 10 is omitted. Incident gamma rays 30 (photons) having an energy of about 100 keV to 2000 keV emitted from the radiation source 6 and incident on the electron drift region are subjected to Compton scattering, which is an interaction with electrons in the gas molecules. As a result, recoil electrons 31 and scattered gamma rays 32 having energy smaller than that of the incident gamma rays 30 are generated. If the energy of the incident gamma ray 30 is E0, the energy of the recoil electrons 31 is Ke, and the energy of the scattered gamma ray 32 is Eγ, the relationship E0 = Ke + Eγ is established.

  While recoil electrons 31 fly in the electron drift region, the recoil electrons 31 interact with gas molecules one after another to be scattered, and generate ionized electrons each time. In FIG. 2, Pc is a Compton scattering point, Pt is a passing point on the recoil electron track, and Pa is an absorption point of the scattered gamma ray 32 by the scattered gamma ray detector 2 (position where the scattered gamma ray is photoelectrically absorbed). . Further, s is an incident direction vector (incident direction unit vector) of the incident gamma ray 30, g is a scattering direction vector (scattering direction unit vector) of the scattered gamma ray 32, and e is a recoil direction vector (Compton scattering) of the recoil electrons 31. (Unit vector in the recoil direction at the point Pc).

  On the line along the track of the recoil electrons 31, an electron cloud 24 composed of a large number of ionized electrons is generated. Recoil electrons 31 gradually lose energy each time they are ionized, and stop when all energy is lost. If the dimension of the electron drift region is 100 mm in the X, Y, and Z directions, the range of the recoil electrons 31 is 100 mm or less if the energy Ke of the recoil electrons 31 is 30 keV or less, and most of the recoil electrons 31 are within the electron drift region. Stop at. In addition, since the scattering interval and the scattering direction received by the recoil electrons 31 are irregular, the shape of the tracks, that is, the electron cloud 24 is also irregularly refracted as shown in the figure. The electron cloud 24 generated in the electron drift region in this way drifts vertically toward the electron collector 11 while maintaining the size and shape substantially by the force received from the electric field.

  The electron collector 11 is a flat plate-like two-dimensional detector such as MSGC (Micro Strip Gas Chamber). This is because a large number of cathode electrode lines C parallel to the Y direction shown in FIG. 2 and arranged at minute intervals in the X direction, and a large number of anodes arranged in the Y direction at an angle of 90 degrees with respect to the cathode electrode line C. Electrode line A is provided as a detection element. By applying a potential difference between the anode electrode line A and the cathode electrode line C, a strong electric field is generated between the electrode lines, whereby the electrons that drift and reach the electron collector 11 are avalanche amplified. A large number of ionized electrons and cations generated as a result are collected by the anode electrode line A and the cathode electrode line C, respectively. The minimum energy of electrons that can be detected by the electron collector 11 is limited by circuit noise and the like, and corresponds to the energy of recoil electrons Ke = about 5 keV. In addition, the maximum energy of detectable electrons is limited by the range of recoil electrons 31 with respect to the size of the electron drift region, and generally corresponds to about Ke = 30 keV.

  The scattered gamma ray detector 2 is arranged behind the electron detector 1 and includes a scintillator 25 and a photoelectric detector 26 in which scintillator elements are two-dimensionally arranged in the X direction and the Y direction. As the photoelectric detector 26, for example, a photomultiplier tube or an avalanche photodiode can be used. The scattered gamma rays 32 are photoelectrically absorbed by the scintillator 25 and converted into visible light, and the visible light is further converted into electric signals by the photoelectric detector 26.

  Next, details of the operation of the signal processing device 4 shown in FIG. 1 will be described. The detection signal of recoil electrons by the electron collector 11 is processed by the electron detection circuit 20, and the detection signal of scattered gamma rays by the scattered gamma ray detector is processed by the gamma ray detection circuit 21. . FIG. 3 shows details of the electron detection circuit 20 and the gamma ray detection circuit 21. Each part of one electron cloud 24 is detected by a plurality of anode electrode lines A and cathode electrode lines C of the electron collector 11, and generates an electrical signal corresponding to the charge (number of electrons). These electric signals continue from the arrival of the front end of the electron cloud 24 to the arrival of the rear end. The electrical signals from the anode electrode line A and the cathode electrode line C are amplified by the amplification units 40a and 40b, respectively, and output to the data capturing unit 41.

  On the other hand, the scattered gamma ray detection signal is amplified by the amplification unit 47 of the gamma ray detection circuit 21. The amplifying unit 47 outputs a signal corresponding to the detection of gamma rays to the data capturing unit 41 of the electronic detection circuit 20 as a trigger signal. The data capturing unit 41 captures all electrical signals for a predetermined time from the trigger signal as a starting point. Here, it is assumed that the predetermined time is set to be D / V or more, where D is the distance between the electron collector 11 and the electrode 12 and V is the drift speed of the electron cloud. As a result, all electrical signals from each electrode line corresponding to one electron cloud 24 are captured.

  The energy Ke of recoil electrons is calculated by the electron energy calculation unit 46 from the electrical signal acquired by the data acquisition unit 41. Furthermore, the electrical signal captured by the data capturing unit 41 is output to the track coordinate calculation unit 42 as a set with time information starting from the trigger signal. For each part of the electron cloud detected by the collector 11, the calculation unit 42 detects the positions (X and Y coordinates) of the detected anode electrode line A and cathode electrode line C, the trigger signal reference drift time ΔT, and the drift velocity V. And the position (Z coordinate) in the direction perpendicular to the collector 11 is calculated. Based on these, three-dimensional position data of each part of the electron cloud 24 is generated.

  Next, the Compton scattering point calculation unit 43 calculates the position (X, Y, Z coordinates) of the Compton scattering point Pc from the extracted three-dimensional position data of each electron cloud, and uses this to calculate the recoil direction vector calculation unit 45. , Output to the gamma ray scattering direction vector calculation unit 51 and the image reconstruction device 23. As shown in FIG. 2, since the incident gamma ray 30 is incident from the electrode 12 side, recoil electrons 31 generated by Compton scattering in the electron drift region fly in the direction of the electron collector 11. Therefore, the position farther from the electron collector 11 among the position data at both ends of the electron cloud 24 is defined as the Compton scattering point Pc. Further, the passing point calculation unit 44 calculates the position (X, Y, Z coordinates) of the passing point Pt on the track separated from the Compton scattering point Pc by a predetermined distance from the three-dimensional position data of the electron cloud 24. Is output to the electronic recoil direction vector calculation unit 45. The predetermined distance only needs to be sufficiently smaller than the range of the recoil electrons 31, and is 2 mm, for example. Based on these data, the recoil direction vector calculation unit 45 calculates a recoil direction vector e which is a unit vector in the direction from the Compton scattering point Pc to the passing point Pt for each electron cloud 24. It outputs to the gamma ray incident direction calculation circuit 22.

  On the other hand, detection signals of individual scattered gamma rays amplified by the amplification unit 47 of the gamma ray detection circuit 21 are taken into the data taking unit 48 and then outputted to the gamma ray absorption point calculating unit 49 and the gamma ray energy calculating unit 50. The gamma ray absorption point calculation unit 49 calculates the position of the absorption point Pa detected when the scattered gamma rays arrive and outputs the data to the gamma ray scattering direction vector calculation unit 51. The gamma ray energy calculation unit 50 calculates the energy Eγ of the detected scattered gamma rays and outputs the data to the gamma ray incident direction calculation circuit 22. The gamma ray scattering direction vector calculation unit 51 calculates the scattering gamma ray scattering direction vector g (scattering direction unit vector) from the Compton scattering point Pc data from the Compton scattering point calculation unit 43 and the scattering gamma ray absorption point Pa data. To do. Then, the data is output to the gamma ray incident direction calculation circuit 22.

  The gamma ray incident direction calculation circuit 22 shown in FIG. 1 is based on recoil electron energy Ke, scattered gamma ray energy Eγ, electron recoil direction vector e, and gamma ray scattering direction vector g for each Compton scattering event. An incident direction vector s is calculated. That is, based on Ke, Eγ, e, and g, the incident direction vector s (incident direction unit vector) of the incident gamma ray is calculated by the following equations (1), (2), and (3). In the equation, m is the stationary mass of electrons, and c is the speed of light.

  In the processing so far, values on an electron detector coordinate system and a scattered gamma ray detector coordinate system described later are used. The image reconstruction device 23 in FIG. 1 first converts the data of the incident direction vector s of the incident gamma ray and the Compton scattering point Pc into values on the device coordinate system described later for a plurality of Compton scattering events. Further, data of the radiation intensity distribution image of the radiation source 6 is generated from the data of the incident direction vector s of the converted incident gamma rays and the Compton scattering point Pc. The display device 5 uses this image data to display the intensity distribution of the radiation according to shading or color difference.

  Next, the adjustment mechanism 3 which is a detector arrangement correcting means will be described. As shown in FIG. 1, the adjustment mechanism 3 of the present embodiment includes an overall drive device 60 and a scattered gamma ray detector drive device 61. The overall drive device 60 includes an in-plane drive mechanism 63 and a first rotation mechanism 64. The in-plane drive mechanism 63 drives the support body 62 that integrally supports the electron detector 1 and the scattered gamma ray detector 2 in the X direction and the Y direction shown in FIG. The first rotation mechanism 64 is mounted on the in-plane drive mechanism 63, and the support 62 is moved in the α direction (rotation direction around the X axis) and β direction (rotation direction around the Y axis) shown in FIG. Rotate. The rotation center of the first rotation mechanism 64 is set to the detector origin Oe in the electron detector coordinate system. In the present embodiment, the scattered gamma ray detector 2 is attached and integrated in advance so as to be parallel to the electron detector 1.

  Next, a method of applying the displacement detection method and the arrangement correction method in the present embodiment to the electron detector 1 and the scattered gamma ray detector 2 in the above Compton camera will be described. FIG. 4 shows a flowchart of displacement detection and arrangement correction. In FIG. 4, steps 1 to 4 correspond to detection of displacement of the electron detector 1 and correction of arrangement, and steps 5 to 8 correspond to detection of displacement of the scattered gamma ray detector 2 and correction of arrangement.

[Step 1: Installation of collimator and reference radiation source]
In order to detect the displacement of the electron detector 1, a first reference radiation source 66a and a collimator 65 are installed on the holding unit 7 as shown in FIG. The collimator 65 is made of a material such as lead having a high radiation shielding capability, and has an internal space that houses the first reference radiation source 66a and an emission hole 67 that penetrates from the internal space to the outside of the collimator. The first reference radiation emitted from the first reference radiation source 66a needs to have a sufficiently high rate of photoelectric absorption in the electron drift region. Therefore, the first reference radiation source 66a is a radiation source that generates first reference radiation (gamma rays or X-rays) having an energy of about 5 keV to 30 keV. In the present embodiment, for example, the radioisotope Fe-55 that emits X-rays having an energy of 5.9 keV is used as the first reference radiation source 66a.

  A perspective view of the collimator 65 is shown in FIG. In this embodiment, the emission hole 67 is a thin circular pinhole as shown in (a), but is not limited to this, and even if it is a cross-shaped through-hole (slit) as shown in (b) Well, both have sufficient depth. Here, an apparatus coordinate system as a position reference, that is, an apparatus origin O and apparatus reference axes Xo, Yo, and Zo are set in the holding unit 7. This apparatus coordinate system is used when a gamma ray distribution image is obtained from information on incident gamma rays obtained by the electronic detection circuit 20 and the gamma ray detection circuit 21 of the Compton camera. Further, when a plurality of Compton cameras are arranged around the inspection object, the reference coordinates are common to all Compton cameras. The collimator 65 is installed such that the emission hole 67 is at a predetermined position in the apparatus coordinate system. In the present embodiment, for example, the center line of the pinhole that is the emission hole 67 is aligned with the apparatus reference axis Zo, and the emission end of the emission hole 67 is set to the apparatus origin O.

  Most of the first reference radiation emitted from the first reference radiation source 66a is absorbed in the collimator 65, and only a part of the first reference radiation is formed as a thin line from the exit hole 67 as shown in FIGS. 6 (a) and 6 (b). It is emitted as a thin planar first reference radiation bundle 68a. The first reference radiation bundle 68a goes straight along the apparatus reference axis Zo and enters the Compton camera.

  On the other hand, an electron detector coordinate system, that is, a detector origin Oe and detector reference axes Xe, Ye, and Ze are defined for the electron detector 1. In the present embodiment, for example, the detector origin Oe is the geometric center of the electron detector 1, the detector reference axis Ze is a center axis perpendicular to the electron collector 11, and the detector reference axes Xe and Ye are detected. Two axes are perpendicular to the instrument reference axis Ze. The scattered gamma ray detector 2 defines a scattered gamma ray detector coordinate system, that is, a detector origin Og and detector reference axes Xg, Yg, and Zg. In the present embodiment, for example, the detector origin Og is the geometric center of the surface of the scintillator 25, the detector reference axis Zg is a center axis perpendicular to the surface of the scintillator 25, and the detector reference axes Xg and Yg are detected. Two axes are perpendicular to the instrument reference axis Zg.

  These electron detector coordinate system and scattered gamma ray detector coordinate system are used when the electron detector circuit 20 and the gamma ray detector circuit 21 obtain position information regarding incident gamma rays from information detected by the electron detector 1 and the scattered gamma ray detector 2. Used. The state in which the electron detector 1 and the scattered gamma ray detector 2 are positioned such that the electron detector coordinate system and the scattered gamma ray detector coordinate system are in a predetermined positional relationship with the apparatus coordinate system is free from displacement (misalignment). Proper placement. The predetermined positional relationship is, for example, a positional relationship in which the X, Y, and Z directions coincide and the origin is offset to a predetermined position. The information on the incident gamma rays obtained by the electron detection circuit 20 and the gamma ray detection circuit 21 is coordinate-converted into the apparatus coordinate system when obtaining a gamma ray distribution image.

Here, the displacements of the electron detector 1 and the scattered gamma ray detector 2 have the following components (1) to (6).
(1) Parallel displacement in the device reference axis Xo direction (2) Parallel displacement in the device reference axis Yo direction (3) Parallel displacement in the device reference axis Zo direction (4) Angular displacement around the device reference axis Xo (α direction) (5 ) Angular displacement around the device reference axis Yo (β direction) (6) Angular displacement around the device reference axis Zo (γ direction) Of these, the detection targets in this embodiment are (3) and (6) Except for four components. (3) and (6) will be mentioned elsewhere.

[Step 2: Displacement detection of electronic detector]
First, a reference value (reference) for the detected displacement will be described. Assume a proper arrangement state in which the relative position of the electron detector coordinate system of the electron detector 1 and the scattered gamma ray detector 2 of the scattered gamma ray detector 2 with respect to the apparatus coordinate system is not displaced (no deviation in arrangement). FIG. 7 is a perspective view showing such a state. In the figure, the chamber 10 is omitted. The detector reference axis Ze of the electron detector coordinate system and the detector reference axis Zg of the scattered gamma ray detector coordinate system both overlap the apparatus reference axis Zo of the apparatus coordinate system. The detector origin Oe in the electron detector coordinate system and the detector origin Og in the scattered gamma ray detector coordinate system are respectively located at a predetermined distance in the Z direction from the apparatus origin O in the apparatus coordinate system.

  In such an appropriate arrangement state, as shown in FIG. 7, the first reference radiation bundle 68a is incident on the electron drift region along the apparatus reference axis Zo. Since the first reference radiation has low energy, it has a very high probability of being photoelectrically absorbed by interacting with electrons in the gas molecules. As a result of photoelectric absorption, ionized electrons are generated, but their energy is small, so the range in the gas is very short. As a result, the ionized electrons interact with the gas molecules one after another only around the photoelectric absorption position and are scattered to generate new ionized electrons. In this way, an electron mass 69 which is a group of many ionized electrons is generated. The size of the electron mass 69 is almost the same as the resolution of the electron detector 1, that is, almost a point when viewed from the detector. The electron mass 69 drifts vertically toward the electron collector 11 while maintaining its size substantially by the force received from the electric field in the electron drift region. When the electron collector 11 is reached, it is amplified by the anode electrode line A and the cathode electrode line C at the arrival position, and ionized electrons and cations are detected. Since neither the parallel displacement nor the angular displacement of the electron detector 1 is present, all the generation positions of the electron mass 69 are on the apparatus reference axis Zo overlapping the first reference radiation bundle 68a.

For example, as shown in FIG. 7, the point G1 (the upper part of the electron drift region), the point G2 (the center of the electron drift region), and the point G3 (the lower part of the electron drift region), which are the generation positions of the electron mass 69, are all device reference axes. It is also on Zo and on the detector reference axis Ze. Therefore, all these electron masses 69 drift along the detector reference axis Ze perpendicular to the electron collector 11. When the electron collector 11 is reached, it is amplified by a specific anode electrode line A ₀ and cathode electrode line C ₀ on the detector reference axis Ze, and ionized electrons and cations are detected.

FIG. 9A is a view of the electron detector 1 having no parallel displacement and no angular displacement as viewed from the Y-axis direction. Further, (b) shows the vicinity of the arrival position of the electron mass 69 of the electron collector 11 in an enlarged manner. Here, C _{−3 to} C ₃ are cathode electrode wires arranged in the X-axis direction. The cathode electrode line C ₀ is located on the detector reference axis Ze (position of X coordinate = 0), and all the electron masses 69 reach the vicinity of the cathode electrode line C _{0 and} are detected regardless of the generation position. Is done. Actually, the arrival position of the electron mass 69 has a fluctuation of about 2 to 3 times the width of the cathode electrode line due to non-uniformity of the electric field in the electron drift region. In this state, measurement of the electron mass 69 (counting of signals detected by each cathode electrode line C) is performed for a predetermined time. An example of the relationship (histogram) between the detected position (cathode electrode line C) and the number of counts is shown in FIG. When the arrangement pitch of the cathode electrode lines C is p, the X coordinate positions of the cathode electrode lines C _{−3 to} C ₃ are −3p to 3p. Signal to be detected is focused on two or three around the cathode electrode lines C ₀ on the detector reference axis Ze, so that symmetrical distribution having a narrow width and a high peak. Such a measurement is performed in advance in the assembly process of the Compton camera, and the value of the half-value width D0 of this distribution is held in the storage device as a reference value (reference). In the illustrated example, D0 = 2p.

  Next, a displacement detection method of the electron detector 1 will be described. FIG. 8 shows a displacement state in which the relative positions of the electron detector coordinate system of the electron detector 1 and the scattered gamma ray detector 2 of the scattered gamma ray detector 2 with respect to the apparatus coordinate system are displaced (there is a dislocation). It is a perspective view. In the figure, the chamber 10 is omitted. As shown in the figure, when the electron detector 1 has a parallel displacement, the first reference radiation bundle 68a is separated from the detector reference axis Ze, so that the points G1, G2, and G3 where the electron mass 69 is generated are It is not on the detector reference axis Ze. These electron masses 69 drift perpendicularly to the electron collector 11 from their respective generation positions, that is, parallel to the detector reference axis Ze. As a result, the electron collector 11 reaches a position away from the detector reference axis Ze, is amplified by the anode electrode line A and the cathode electrode line C at the arrival position, and ionized electrons and cations are detected.

Further, when there is an angular displacement of the electron detector 1, the first reference radiation bundle 68a is not parallel to the detector reference axis Ze. When the electron mass 69 generated at the points G1, G2, and G3 having different distances from the electron collector 11 drifts perpendicularly to the electron collector 11, that is, parallel to the detector reference axis Ze, each of the electron collectors 11 Reach different positions. Then, it is amplified by a plurality of anode electrode lines A and cathode electrode lines C at the arrival position, and ionized electrons and cations are detected. FIG. 11A is a view of the electron detector 1 having parallel displacement and angular displacement as viewed from the Y-axis direction. Further, (b) shows the vicinity of the arrival position of the electron mass 69 of the electron collector 11 in an enlarged manner. Here, C _{−8 to} C ₂ are cathode electrode wires arranged in the X-axis direction. Although the cathode electrode line C ₀ is located on the detector reference axis Ze, the electron mass 69 reaches each different cathode electrode line C and is detected depending on the distance from the electron collector 11 at the generation position. Is done. That is, the electron mass 69 generated at the point G1 farthest from the electron collector 11 reaches the cathode electrode line C- ₂ , and the electron mass 69 generated at the intermediate point G2 reaches the cathode electrode line C- ₄ and is the closest. The electron mass 69 generated at the point G2 reaches the cathode electrode line C- ₆ .

  Here, the rate at which the first reference radiation incident in the electron drift region interacts with electrons in the gas molecules and is photoelectrically absorbed is large at the front end where the first reference radiation bundle 68a is incident, and the rear end. Then it gets smaller. For example, when the distance L between the electrode 12 and the electron collector 11 is set to 100 mm, the rate of photoelectric absorption of X-rays having an energy of 5.9 keV is about 0 in the middle of the electron drift region when the vicinity of the electrode 12 is 1. .15, around 0.02 near the electron collector 11. As described later, as a result of the difference in the photoelectric absorption ratio depending on the position, the distribution of the count number becomes asymmetric in the electron collector 11, and this is used to not only measure the magnitude (absolute value) of the angular displacement, You can see which direction it is tilted.

In this state, the electron mass 69 is measured for a predetermined time (the count of signals detected by each cathode electrode line). An example of the relationship (histogram) between the detected position (cathode electrode line C) and the number of counts is shown in FIG. X-coordinate position of the cathode electrode line _C -8 -C ₂ becomes -8P～2p. Signal to be detected is dispersed in the detector reference axis 6-7 present with the C _-4 centers spaced from the cathode electrode lines C ₀ on Ze, form a distribution asymmetric with a peak biased and wide. Here, the distance D1 (distribution position) from the center of this distribution to the cathode electrode line C ₀ (X coordinate = 0) is parallel to the apparatus reference axis Zo of the detector reference axis Ze of the electron detector 1 in the X direction. Corresponds to displacement. That is, if the parallel displacement in the X-axis direction with respect to the apparatus reference axis Zo of the electron detector 1 is ΔXe, ΔXe = D1. In the illustrated example, since the X coordinate of the center of the distribution is −4p, ΔXe = 4p.

Further, the distribution width D2, that is, the distance from the end of the distribution with a small count number to the end of the distribution with a large count number is the β direction (around the Y axis) of the detector reference axis Ze of the electron detector 1 with respect to the apparatus reference axis Zo. Corresponds to the angular displacement of. When the value a [Delta] [theta] _beta becomes _{Δθ β = (D2-D0)} / L. D0 is the width (spread) of the distribution in the above-described proper arrangement state without displacement, and uses the reference value held in the storage device. In the illustrated example, the X coordinate at the end of the distribution with a small count number is −7p, the X coordinate at the end of the distribution with a large count number is −p, and Δθ _β = 4p / L. As described above, it is possible to detect not only the magnitude of the angular displacement but also the direction by distinguishing between the count numbers at both ends of the distribution.

Similarly, it is possible from the detection signal by the anode electrode lines A, detects an angular displacement [Delta] [theta] _alpha parallel displacement ΔYe the alpha direction of the Y-axis direction with respect to the apparatus reference axis Zo electron detector 1 (X-axis). The above-described measurement of the electron mass and the detection of the magnitude and direction of the parallel displacement and the angular displacement are performed by detection means provided inside or outside the Compton camera.

[Step 3: Permitted / Unacceptable]
The detected parallel displacements ΔXe, ΔYe and the angular displacements Δθ _β , Δθ _α are compared with a preset upper limit value to determine whether they are within an allowable range. If the displacement is within the allowable range (smaller than the upper limit value), the correction is not necessary, and the process proceeds to the displacement detection of the scattered gamma ray detector in step 5 of FIG. If the displacement is outside the allowable range (greater than or equal to the upper limit value), the electron detector arrangement in step 4 is corrected.

[Step 4: Correction of electron detector arrangement]
Next, the arrangement of the electron detector 1 is corrected. In the present embodiment, the adjustment mechanism 3 is used for correcting the arrangement of the electron detector 1. The adjustment mechanism 3 is driven so as to correct the parallel displacements ΔXe and ΔYe and the angular displacements Δθ _β and Δθ _α of the electron detector 1 detected in step 2 of FIG. The procedure is as follows (1) to (4). It is not necessary to be in the order of (1), (2), (3), (4), and the order is completely arbitrary.
(1) The first rotation mechanism 64 drives the support 62 in the β direction by −Δθ _β (2) The first rotation mechanism 64 drives the support 62 in the α direction by −Δθ _α (3) surface The inner drive mechanism 63 drives the support in the X direction by -ΔXe. (4) The in-plane drive mechanism 63 drives the support in the Y direction by -ΔYe.

  In order to confirm the result of this correction, the detection of the displacement of the electron detector in step 2 in FIG. If the displacement is within the allowable range in step 3 (smaller than the upper limit value), the correction of the arrangement of the electron detector 1 is completed, and the detection of the displacement of the scattered gamma rays and the correction of the arrangement (steps 5 to 8 in FIG. 4). Migrate to 4 is a process in which, for example, a program for realizing one or more functions is supplied to a device via a network or a storage medium, and one or more processors in the computer of the device read and execute the program. It is feasible. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions. The same applies to the procedure of the flowchart described later.

[Step 5: Installation of reference radiation source]
In order to detect the displacement of the scattered gamma ray detector 2, a second reference radiation source 66b and a collimator 65 are installed on the holding unit 7 as shown in FIG. The collimator 65 can also be the one used for detecting the displacement of the electron detector 1 in step 1, but a dedicated one having a higher radiation shielding capability by increasing the thickness may be used. The second reference radiation emitted by the second reference radiation source 66b must pass through the electron detector 1 and reach the scattered gamma ray detector 2. Therefore, the second reference radiation source 66b is a radiation source that generates second reference radiation (gamma rays) having an energy of about 100 keV to 1000 keV that is at least larger than the first reference radiation. In the present embodiment, for example, a radioisotope Cs-137 that emits gamma rays having an energy of 662 keV is used. As shown in FIG. 6, only a part of the second reference radiation emitted from the second reference radiation source 66b is emitted from the exit hole 67 as a thin linear or thin planar second reference radiation bundle 68b. . The second reference radiation bundle 68b travels straight along the apparatus reference axis Zo, passes through the electron detector 1 of the Compton camera, and enters the scattered gamma ray detector 2.

[Step 6: Displacement detection of scattered gamma ray detector]
As described above, the scattered gamma ray detector 2 is attached in advance so as to be parallel to the electron detector 1. Therefore, when the displacement of the electron detector 1 is determined to be within the allowable range in Step 3 of FIG. 4, the angular displacement of the scattered gamma ray detector 2 is also within the allowable range. Therefore, in this embodiment, only the detection of the parallel displacement of the scattered gamma ray detector 2 and the correction of the arrangement are performed.

A displacement detection method of the scattered gamma ray detector 2 will be described. FIG. 13 is a view of the scattered gamma ray detector 2 with parallel displacement as viewed from the Y-axis direction. Here, S _{−5 to} S ₅ are scintillator elements arranged in the X direction. Although the scintillator elements S ₀ is on the detector reference axis Zg are located, since the second reference radiation beam 68b is spaced from the detector reference axis Zg, the detection position of the second reference radiation detector reference There is no axis Zg.

In this state, measurement of the second reference radiation (counting of signals detected by each scintillator element) is performed for a predetermined time. An example of the relationship (histogram) between the detected position (scintillator element S) and the number of counts is shown in FIG. When the arrangement pitch of the scintillator elements and q, X-coordinate position of the scintillator elements _S -5 to S ₅ becomes -5Q～5q. Signal detected is concentrated scintillator elements S _-2 which spaced from the scintillator element S ₀ that is on the detector reference axis Zg. Here, the scintillator elements _{S -2} distance D3 from the (X coordinate = -2Q) to scintillator elements _S 0 (X coordinate = 0) signal is concentrated, the scattered gamma ray detector 2 detector reference axis system criteria Zg This is a parallel displacement in the X direction with respect to the axis Zo. That is, if the parallel displacement in the X-axis direction with respect to the apparatus reference axis Zo of the scattered gamma ray detector 2 is ΔXg, ΔXg = D3, and in the illustrated example, ΔXg = 2q. Similarly, the parallel displacement ΔYg in the Y direction with respect to the apparatus reference axis Zo can be detected. The measurement of the second reference radiation and the detection of the magnitude and direction of the parallel displacement are also performed by detection means provided inside or outside the Compton camera.

[Step 7: Acceptable / unacceptable]
The detected parallel displacements ΔXg and ΔYg are compared with a preset upper limit value, and it is determined whether or not they are within an allowable range. If the displacement is within the allowable range (smaller than the upper limit value), the correction is unnecessary and the operation is terminated. If the displacement is outside the allowable range (greater than the upper limit value), the arrangement of the scattered gamma ray detectors in step 8 is corrected.

[Step 8: Correction of Arrangement of Scattering Gamma Ray Detector]
Next, a method for correcting the arrangement of the scattered gamma ray detector 2 according to the detected displacement will be described. In the present embodiment, the adjustment mechanism 3 is used for correcting the arrangement of the scattered gamma ray detector 2. The adjustment mechanism 3 is driven so as to correct the parallel displacements ΔXg and ΔYg of the scattered gamma ray detector 2 detected in step 6 of FIG. The procedure is as follows (1) and (2). The order does not matter.
(1) The scattering gamma ray detector driving device 61 drives the scattering gamma ray detector 2 in the X direction by -ΔXg. (2) The scattering gamma ray detector driving device 61 drives the scattering gamma ray detector 2 in the Y direction by -ΔYg.

  In order to confirm the result of this correction, the detection of the displacement of the scattered gamma ray detector in step 6 in FIG. If the displacement is within the allowable range in step 7 (smaller than the upper limit value), the correction of the arrangement of the scattered gamma ray detector 2 ends. In this embodiment, it is not possible to detect the displacement of the scattered gamma ray detector and correct the displacement first, and then to detect the displacement and correct the displacement of the electronic detector. That is, when the first rotation mechanism 64 is driven in step 4, the horizontal position of the scattered gamma ray detector 2 also changes. Therefore, the displacement detection and position adjustment (step 8) of the scattered gamma ray detector must be performed after that (electronic After detector displacement detection and displacement correction).

(Embodiment 2)
FIG. 15 shows a schematic configuration of a second embodiment of a Compton camera to which the detector displacement detection method and the detector arrangement correction method according to the present invention are applied. In the first embodiment shown in FIG. 1, the adjusting mechanism 3 is used for correcting the arrangement of the detectors. In contrast, the second embodiment does not use an adjustment mechanism for correcting the arrangement of the electron detector 1 and the scattered gamma ray detector 2, and includes a correction unit that corrects position information obtained from the detector. 4 is different from the first embodiment. Since the other Compton cameras have the same configuration and operation as those of the first embodiment, description thereof will be omitted. Further, the collimator 65, the first reference radiation source 66a, the second reference radiation source 66b, the apparatus coordinate system, the electron detector coordinate system, and the scattered gamma ray detector coordinate system used for detecting the displacement of the detector are all embodiments. The description is omitted because it is the same as 1.

  A method for correcting the arrangement of the electron detector 1 and the scattered gamma ray detector 2 in this embodiment will be described. FIG. 18 shows details of the electron detection circuit 20 and the gamma ray detection circuit 21 of the present embodiment. Here, 71 is a storage device, and 72a, 72b, 72c are position correction units. All other configurations and operations are the same as those of the first embodiment shown in FIG. Here, the electron detector 1 and the scattered gamma ray detector 2 are assumed to have a parallel displacement and an angular displacement with respect to the apparatus coordinate system. These displacements are detected in advance by a method described later, and all of the information is stored in the storage device 71. In the present embodiment, the correction of the arrangement of the detectors is performed as follows in the signal processing when obtaining the gamma ray distribution image of the target radiation source 6.

  As described above, the electrical signal corresponding to each part of one electron cloud is amplified by the amplification units 40 a and 40 b and output to the data capturing unit 41. The energy Ke of each recoil electron is calculated by the electron energy calculation unit 46 from the electric signal acquired by the data acquisition unit 41. Further, the track coordinate calculation unit 42 generates three-dimensional position data of each part of the electronic cloud from the signal captured by the data capture unit 41. The Compton scattering point calculation unit 43 calculates the position of the Compton scattering point Pc from this data. What is calculated here is a coordinate value on the displaced electron detector coordinate system. Accordingly, the position correction unit 72a corrects the coordinate value with reference to the parallel displacement and angular displacement information of the electron detector 1 stored in the storage device 71. As a result, the correct coordinate value of the Compton scattering point Pc when it is assumed that the electron detector 1 is not displaced is obtained.

  Similarly, the position of the passing point Pt is calculated by the passing point calculation unit 44. What is calculated here is also a coordinate value on the displaced electron detector coordinate system. Therefore, the position correction unit 72b corrects the coordinate value with reference to the parallel displacement and angular displacement information of the electron detector 1 stored in the storage device 71. As a result, the correct coordinate value of the passing point Pt when it is assumed that the electron detector 1 is not displaced is obtained. Based on these corrected data, the electron recoil direction vector calculation unit 45 calculates a recoil direction vector e that is a unit vector in a direction from the Compton scattering point Pc to the passing point Pt for each electron cloud. This is output to the gamma ray incident direction calculation circuit 22 of FIG.

  On the other hand, detection signals of individual scattered gamma rays amplified by the amplification unit 47 of the gamma ray detection circuit 21 are taken into the data taking unit 48 and then outputted to the gamma ray absorption point calculating unit 49 and the gamma ray energy calculating unit 50. The gamma ray energy calculation unit 50 calculates the energy Eγ of the detected scattered gamma rays and outputs the data to the gamma ray incident direction calculation circuit 22. Further, the gamma ray absorption point calculation unit 49 calculates the position of the absorption point Pa detected when the scattered gamma rays arrive. What is calculated here is a coordinate value on the displaced scattered gamma ray detector coordinate system. Therefore, the position correction unit 72c performs parallel displacement and angular displacement of the scattered gamma ray detector 2 stored in the storage device 71 with respect to the coordinate value (in the configuration of the first embodiment, it is equivalent to the angular displacement of the electron detector 1). ) And make corrections. As a result, the correct coordinate value of the absorption point Pa is obtained when it is assumed that the scattered gamma ray detector 2 is not displaced.

  The gamma ray scattering direction vector calculation unit 51 calculates a scattering direction vector g (scattering direction unit vector) of the scattered gamma rays from the corrected Compton scattering point Pc data and the corrected scattered gamma ray absorption point Pa data. Then, the data is output to the gamma ray incident direction calculation circuit 22.

  The gamma ray incident direction calculation circuit 22 is configured to input the incident gamma ray based on the recoil electron energy Ke, the scattered gamma ray energy Eγ, the corrected electron recoil direction vector e, and the corrected gamma ray scattering direction vector g. A direction vector s is calculated. That is, the incident direction vector s (incident direction unit vector) of the incident gamma ray is calculated using the above-described equations (1), (2), and (3). The image reconstruction device 23 converts the incident direction vector s of each incident gamma ray and the calculated value of the Compton scattering point Pc into values on the device coordinate system. Furthermore, data of a radiation intensity distribution image of the radiation source 6 is generated from these data, and the display device 5 displays the intensity distribution of the radiation by shading and color difference using this image data.

  Next, a detector displacement detection method according to this embodiment will be described. FIG. 16 shows a displacement detection flowchart. In FIG. 16, steps 1 to 3 correspond to detection of displacement of the electron detector 1, and steps 4 to 6 correspond to detection of displacement of the scattered gamma ray detector 2.

[Step 1: Installation of collimator and reference radiation source]
In order to detect the displacement of the electron detector 1, a first reference radiation source 66a and a collimator 65 are installed on the holding unit 7 as shown in FIG. Since this step is the same as step 1 of the first embodiment, detailed description thereof is omitted.

[Step 2: Displacement detection of electronic detector]
The electron mass 69 generated in the electron drift region is measured for a predetermined time (signals detected by each cathode electrode line C and anode electrode line A are counted). As a result, parallel displacements ΔXe and ΔYe and angular displacements Δθ _α and Δθ _β with respect to the apparatus reference axis Zo of the electronic detector 1 are detected. Since this step is the same as step 2 in the first embodiment, detailed description thereof is omitted.

[Step 3: Save displacement to storage]
Information on the parallel displacements ΔXe and ΔYe and the angular displacements Δθ _α and Δθ _β detected in step 2 is stored in the storage device 71, and the detection of the displacement of the electron detector 1 is terminated.

[Step 4: Installation of reference radiation source]
In order to detect the displacement of the scattered gamma ray detector 2, a second reference radiation source 66b and a collimator 65 are installed on the holding unit 7 as shown in FIG. Since this step is the same as step 5 in the first embodiment, detailed description thereof is omitted.

[Step 5: Displacement detection of scattered gamma ray detector]
The second reference radiation is measured for a predetermined time (a signal detected by each scintillator element S is counted). As a result, the parallel displacements ΔXg and ΔYg of the scattered gamma ray detector 2 with respect to the apparatus reference axis Zo are detected. Since this step is the same as step 6 in the first embodiment, detailed description thereof is omitted.

[Step 6: Save displacement in storage]
Information on the parallel displacements ΔXg and ΔYg of the scattered gamma ray detector 2 detected in step 5 is stored in the storage device 71, and the displacement detection of the scattered gamma ray detector 2 is terminated.

  In the first and second embodiments described above, the emission hole 67 of the collimator 65 is a thin circular pinhole shown in FIG. 6A, but a cross-shaped through-hole (slit) shown in FIG. 6B. However, the displacement can be detected by the same method. This is because even if the cross section of the bundle of radiation is a cross, etc., each contained radiation is a straight line, so the electron cloud and scattered gamma rays that are generated are not different from the case of a thin circular pinhole. is there. In the latter case, it is assumed that the direction of the cross is directed in the X direction and the Y direction. By combining two slits each having a narrow width W in the X direction and the Y direction in this way, the area of the entire emission hole 67 can be increased as compared with a single thin pinhole, so that the radioactivity of the reference radiation source is increased. Without increasing the intensity (number of photons) of the reference radiation. As a result, efficiency can be improved, such as shortening the measurement time in displacement detection. In FIG. 6B, the reference radiation bundle is drawn as a parallel bundle, but it is sufficient that at least the radiation angle in the width W direction is sufficiently limited.

(Embodiment 3)
FIG. 19 shows a schematic configuration of a third embodiment of a Compton camera to which the detector displacement detection method and the detector arrangement correction method according to the present invention are applied. In the present embodiment, the adjustment mechanism 3 is used to correct the arrangement of the electron detector 1 and the scattered gamma ray detector 2 as in the first embodiment, but the configuration is different.

  The adjustment mechanism 3 includes an overall drive device 60 and a scattered gamma ray detector drive device 61. The overall drive device 60 includes an in-plane drive mechanism 63, a second rotation mechanism 70, and a first rotation mechanism 64. The in-plane drive mechanism 63 drives the support body 62 that integrally supports the electron detector 1 and the scattered gamma ray detector 2 in the X direction and the Y direction shown in FIG. The second rotation mechanism 70 is mounted on the in-plane drive mechanism 63 and rotates the support body 62 in the γ direction (rotation direction around the Z axis) shown in FIG. The first rotation mechanism 64 is mounted on the second rotation mechanism 70, and the support 62 is arranged in the α direction (rotation direction around the X axis) and β direction (rotation direction around the Y axis) shown in FIG. Turn to.

  In the present embodiment, since the configuration and operation of the Compton camera excluding the adjustment mechanism 3 are the same as those in the first embodiment, description thereof will be omitted. In this embodiment, as will be described later, a collimator 65 used for detecting the displacement of the detector is also different from that of the first embodiment. Since the other apparatus coordinate system, electron detector coordinate system, and scattered gamma ray detector coordinate system are all the same as those in the first embodiment, description thereof will be omitted.

  Next, a method of applying the detector displacement detection method and the detector arrangement correction method to the electron detector 1 and the scattered gamma ray detector 2 will be described. The flowchart of displacement detection and arrangement correction is the same as that of the first embodiment shown in FIG. 4. Steps 1 to 4 correspond to displacement detection and arrangement correction of the electron detector 1, and steps 5 to 8 are scattered gamma ray detection. This corresponds to the detection of the displacement of the device 2 and the correction of the arrangement.

[Step 1: Installation of collimator and reference radiation source]
In order to detect the displacement of the electron detector 1, a first reference radiation source 66a and a collimator 65 are installed on the holding unit 7 as shown in FIG. The collimator 65 is made of a material such as lead having a high radiation shielding capability, and is formed with two exit holes 67-1 and 67-2 penetrating from the internal space and the internal space to the outside of the collimator. The first reference radiation source 66 a is a radiation source that generates first reference radiation (gamma rays or X-rays) having an energy of about 5 keV to 30 keV, and is accommodated in the internal space of the collimator 65. In the present embodiment, for example, the radioisotope Fe-55 that emits X-rays having an energy of 5.9 keV is used as the first reference radiation source 66a.

  A perspective view of the collimator 65 is shown in FIG. The exit holes 67-1 and 67-2 are small circular pinholes as shown in the figure, and have a sufficient depth.

  Here, an apparatus coordinate system as a position reference, that is, an apparatus origin O and apparatus reference axes Xo, Yo, and Zo are set in the holding unit 7. This apparatus coordinate system is used when a gamma ray distribution image is obtained from information on incident gamma rays obtained by the electronic detection circuit 20 and the gamma ray detection circuit 21 of the Compton camera. The collimator 65 is installed so that the emission holes 67-1 and 67-2 are at predetermined positions in the apparatus coordinate system. For example, the center lines of the pinholes that are the emission holes 67-1 and 67-2 are parallel to the apparatus reference axis Zo, and the coordinates of the emission end of the emission hole 67-1 in the apparatus coordinate system are (u, -u). , 0), and the coordinates of the exit end of the exit hole 67-2 in the apparatus coordinate system are (−u, u, 0). That is, the exit end of the exit hole 67-1 and the exit end of the exit hole 67-2 are symmetric with respect to the apparatus origin O, and the line connecting them is 45 with respect to the apparatus reference axis Xo and the apparatus reference axis Yo. Make an angle of degrees. In the present embodiment, an electron detector using the first reference radiation bundle 68a-1 emitted from the emission hole 67-1 and the first reference radiation bundle 68a-2 emitted from the emission hole 67-2. 1 displacement is detected.

Here, the displacements of the electron detector 1 and the scattered gamma ray detector 2 have the following components (1) to (6).
(1) Parallel displacement in the device reference axis Xo direction (2) Parallel displacement in the device reference axis Yo direction (3) Parallel displacement in the device reference axis Zo direction (4) Angular displacement around the device reference axis Xo (α direction) (5 ) Angular displacement around the device reference axis Yo (β direction) (6) Angular displacement around the device reference axis Zo (γ direction) Of these, the detection targets in this embodiment are the five components excluding (3) It is. (3) can be detected and corrected by another simple method, as will be described later.

[Step 2: Detection of displacement of the electronic detector 1]
Hereinafter, a specific embodiment when the detector displacement detection method and the detector arrangement correction method according to the present embodiment are applied to a Compton camera will be described. First, the parallel displacement of the electron detector 1 at the position corresponding to each of the first reference radiation bundles 68a-1 and 68a-2 corresponds to one of the first reference radiation bundles 68a-1 and 68a-2. Detect the angular displacement at the position. The first reference radiation beam 68a-1 where, become a standard, and the cathode electrode line C _u is the X coordinate = u on the detector reference axis Xe, Y coordinate on the detector reference axis Ye = - an anode electrode lines _{a -u} is u. With respect to the first reference radiation beam 68a-2, become a standard, and the cathode electrode line C _-u is X coordinate = -u on the detector reference axis Xe, Y coordinate on the detector reference axis Ye = U is the anode electrode line _Au .

The displacement detection method is the same as in step 2 of the first embodiment. For the first reference radiation bundle 68a-1, the measurement of the electron mass 69 is performed for a predetermined time (the signal detected by each cathode electrode line C and anode electrode line A). Count). Then determine the center position Xe1 of the distribution of the detection signal of the cathode electrode line C, the distance to the position u of the cathode electrode line C _u as a reference, i.e. a X-axis direction displacement DerutaXe1. Also, the distance from the center position Ye1 of the distribution of the detection signal of the anode electrode line A to the position -u of the reference anode electrode line A- _u , that is, the displacement in the Y-axis direction is obtained as ΔYe1. That is, the relationship between the detected position and the displacement is Xe1 = ΔXe1 + u and Ye1 = ΔYe1-u.

Similarly, for the first reference radiation bundle 68a-2, the electron mass 69 is measured for a predetermined time. Then, the distance from the center position Xe2 of the distribution of the detection signal of the cathode electrode line C to the position -u of the cathode electrode line C- _u serving as a reference, that is, the displacement ΔXe2 in the X-axis direction is obtained. Further, from the center position Ye2 of the distribution of the detection signal of the anode electrode lines A, the distance to the position u of the anode electrode lines A _u as a reference, i.e. a displacement in the Y-axis direction determine the DerutaYe2. That is, the relationship between the position and displacement in the electron detector coordinate system is Xe2 = ΔXe2-u and Ye2 = ΔYe2 + u.

  From the obtained Xe1, Ye1, Xe2, and Ye2, three components of displacement perpendicular to the device reference axis Zo of the electron detector 1, that is, angular displacement Δθγ around the device reference axis Zo (γ direction), X direction The parallel displacement ΔXe and the parallel displacement ΔYe in the Y direction are calculated. For this, the following formulas (4), (5), and (6) are used.

Further, for the first reference radiation bundle 68a-1 or 68a-2, the angular displacement Δθ _α about the X axis and the angular displacement about the Y axis are determined from the width of the distribution of the signals detected by the cathode electrode line C and the anode electrode line A. Δθ _β is obtained. The distribution width of this signal is the distance from the end of the distribution with a small count number to the end of the distribution with a large count number.

[Step 3: Permitted / Unacceptable]
The detected displacement is compared with a preset upper limit value, and it is determined whether or not it is within an allowable range. If the displacement is within the allowable range (smaller than the upper limit value), the correction is not necessary, and the process proceeds to the displacement detection of the scattered gamma ray detector in step 5 of FIG. On the other hand, if the displacement is outside the allowable range (greater than the upper limit value), the arrangement of the electron detectors in step 4 is corrected.

[Step 4: Correction of electron detector arrangement]
Next, the arrangement of the electron detector 1 is corrected. In the present embodiment, the adjustment mechanism 3 is used for correcting the arrangement of the electron detector 1. The adjustment mechanism 3 is driven so as to correct the parallel displacements ΔXe, ΔYe and the angular displacements Δθ _γ , Δθ _α , Δθ _β detected in step 2 above. The procedure is as follows (1) to (5).
(1) The support 62 is driven in the β direction by −Δθ _β by the first rotation mechanism 64 (2) The support 62 is driven in the α direction by −Δθ _α by the first rotation mechanism 64 (3) the second rotating mechanism 70 -Δθ _γ driving the support 62 in the gamma direction (4) by a surface within the drive mechanism 63 to -ΔXe drive the support in the X direction (5) support by the in-plane drive mechanism 63 -ΔYe drive in Y direction

  In order to confirm the result of this correction, the detection of the displacement of the electron detector in step 2 in FIG. In Step 3, if the displacement is within the allowable range (smaller than the upper limit value), the correction of the arrangement of the electron detector 1 is finished, and the detection of the displacement of the scattered gamma ray detector and the correction of the arrangement (Steps 5 to 8). Migrate to

  Hereinafter, step 5 (installation of the reference radiation source) to step 8 (correction of the arrangement of the scattered gamma ray detectors) are the same as those in the first embodiment, and thus description thereof is omitted.

The parallel displacement of the electron detector 1 and the scattered gamma ray detector 2 in the apparatus reference axis Zo direction can be easily detected by using a general method such as a gauge or various distance measuring means. Therefore, if such a general method and the displacement detection method according to the present invention are combined, all components of the displacement of the electron detector 1 and the scattered gamma ray detector 2, that is, the following (1) to (6): The component can be detected.
(1) Parallel displacement in the device reference axis Xo direction (2) Parallel displacement in the device reference axis Yo direction (3) Parallel displacement in the device reference axis Zo direction (4) Angular displacement around the device reference axis Xo (α direction) (5 ) Angular displacement around the device reference axis Yo (β direction) (6) Angular displacement around the device reference axis Zo (γ direction)

  Further, when a plurality of Compton cameras are arranged around the inspection object, the detector displacement detection method and the detector arrangement correction method according to the present invention can be applied to each Compton camera. In this case, the first reference radiation source, the second reference radiation source, and the collimator are made common, and the first reference radiation bundle and the second reference radiation bundle may be individually emitted to each Compton camera. Good.

1 Electron detector 2 Gamma ray detector (scattered gamma ray detector)
3 Adjustment mechanism 4 Signal processing device 6 Radiation source 11 Electron collector 12 Electrode (Electronic drift means)

Claims (18)

A Compton camera displacement detection method comprising a scatterer, an electron drift means, an electron detector having an electron collector, and a gamma ray detector,
Injecting a linear or planar first reference radiation bundle into the scatterer;
Moving ionized electrons generated by the interaction of the first reference radiation flux and the scatterer to the electron collector by the drift means;
Detecting the displacement of the electron detector from a predetermined position based on the distribution of the first detection signal of the ionized electrons detected by the electron collector;
A displacement detection method characterized by comprising:   The displacement detection method according to claim 1, wherein the first detection signal includes detection signals of ionized electrons generated at a plurality of positions in the scatterer having different distances from the electron collector. .   A parallel displacement in a direction perpendicular to an incident direction of the first reference radiation bundle of the electron detector is detected based on a position of a distribution of the first detection signal in the electron collector. The displacement detection method according to claim 1 or 2.   The angular displacement of the electron detector with respect to the incident direction of the first reference radiation bundle is detected based on a spread of the distribution of the first detection signal in the electron collector. The displacement detection method according to any one of the above.   The first reference radiation bundle is composed of a plurality of reference radiation bundles incident on different positions of the electron collector, and based on the distribution of the first detection signal in the electron collector, The displacement detection method according to claim 1, wherein a parallel displacement in a direction perpendicular to an incident direction of the first reference radiation bundle and an angular displacement around the incident direction are detected.   A step of causing a linear or planar second reference radiation bundle having energy higher than that of the first reference radiation bundle to enter the gamma ray detector, and the second detection signal from the gamma ray detector based on the second detection signal. The displacement detection method according to any one of claims 1 to 5, further comprising a step of detecting a displacement of the gamma ray detector from a predetermined position. An electron detector having a scatterer, an electron drift means and an electron collector, and a Compton camera arrangement correction method comprising a gamma ray detector,
6. An arrangement correction method, wherein the arrangement of the electron detectors is corrected in accordance with displacement information obtained by the displacement detection method according to any one of claims 1 to 5. An electron detector having a scatterer, an electron drift means and an electron collector, and a Compton camera arrangement correction method comprising a gamma ray detector,
An arrangement correction method, wherein the arrangement of the gamma ray detectors is corrected in accordance with displacement information obtained by the displacement detection method according to claim 6. A Compton camera comprising a scatterer, an electron drift means, an electron detector having an electron collector, and a gamma ray detector,
A Compton camera comprising a drive mechanism for correcting the arrangement of the electron detectors.   The drive mechanism corrects the arrangement of the electron detectors according to displacement information obtained by the displacement detection method according to any one of claims 1 to 5. Compton camera. A Compton camera comprising a scatterer, an electron drift means, an electron detector having an electron collector, and a gamma ray detector,
A Compton camera comprising: a correction unit that corrects position information of ionized electrons generated by an interaction between a reference radiation bundle obtained from the electron detector and the scatterer.   The said correction | amendment part correct | amends the positional information of the said ionization electron according to the information of the displacement obtained by the displacement detection method of any one of Claim 1-5. Compton camera. A Compton camera comprising a scatterer, an electron drift means, an electron detector having an electron collector, and a gamma ray detector,
A Compton camera comprising a drive mechanism for correcting the arrangement of the gamma ray detectors.   The Compton camera according to claim 13, wherein the driving mechanism corrects the arrangement of the gamma ray detectors in accordance with displacement information obtained by the displacement detection method according to claim 6. Electron detector having a scatterer, electron drift means, and an electron collector, and a gamma ray detector for detecting scattered gamma rays due to Compton scattering, which is an interaction between photons incident on the electron drift means and electrons of the scatterer Compton camera with
A Compton camera comprising a correction unit that corrects position information of scattered gamma rays obtained from the gamma ray detector.   The Compton camera according to claim 5, wherein the correction unit corrects position information of the scattered gamma rays according to displacement information obtained by the displacement detection method according to claim 5.   Ionized electrons and scattered gamma rays due to Compton scattering, which are interactions between photons incident on the electron drift means and electrons of the scatterer, obtained by the electron detector and the gamma ray detector, respectively, after correction of the arrangement The Compton camera according to any one of claims 9, 10, 13, and 14, wherein information on an incident direction of an incident gamma ray is acquired based on the information.   Information on the incident direction of incident gamma rays using information on ionized electrons or scattered gamma rays due to Compton scattering, which is an interaction between photons incident on the electron drift means and electrons of the scatterer, obtained by the correction unit. The Compton camera according to claim 11, wherein the Compton camera is acquired.

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