JP2706957B2 - Radiation source image reconstruction device - Google Patents

Description

The present invention relates to an apparatus for reconstructing an image of a radiation source.

[Related Art] Radio waves and ordinary light can easily form an image by utilizing the optical properties of reflection and refraction. This is because the lens or the concave mirror itself has an arithmetic function for making a one-to-one correspondence between a subject and an image via electromagnetic waves. However, it is difficult to form an image because radiation does not reflect or refract, or is difficult to use in optics. But,
Image reconstruction devices for X-ray and gamma-ray sources have been developed and used in the fields of astronomical observation, medical treatment and nondestructive inspection using several physical principles. For example, (a) a single photon emission CT or a positron emission tomography apparatus uses a detector to rotationally scan around a γ-ray source and reconstruct an image by calculation. (B) A scinti-scanner or γ-ray In the spectroscopic telescope, various collimators, such as a single-hole or focus type, scan the γ-ray source and reconstruct the image. (C) The scintillation camera uses a multihole detector and multiple detectors to detect adjacent (D) The X-ray oblique incidence reflection telescope can reflect when the incident angle of low energy X-rays with respect to the concave mirror is large. (E) the coded mask imager interposes a coded mask obtained from a mathematical cyclic difference set between a source and a detector, and forms an image by calculation. Reconfigure, equipment, etc. That.

[Problems to be Solved by the Invention] These conventional radiation source image reconstruction apparatuses are limited to images of X-rays and low energy γ-ray sources, and include α-rays, β-rays, high-energy γ-rays, neutron rays, Devices for obtaining source images such as proton beams and fission fragments have not been developed yet. Also, in the prior art, the device of (a) must be larger than the object which is the source, and the devices of (a) and (b) both mechanically scan the object, so that high precision scanning and A detection mechanism is required. The focal collimator of the device (b) has a fixed distance to the subject. The device (c) has a reduced angular resolution as the distance to the source increases. (D) The device does not glare to high energy X-rays. In addition, the apparatus becomes large because the focal length of the concave mirror is long. The apparatus (e) is not effective for high energy γ-rays, and the apparatus becomes large when trying to increase the angular resolution. was there.

The apparatus according to the present invention utilizes the fact that radiation has transparency and rectilinearity with respect to a substance as an rather advantageous property, and aims to obtain various radiation images easily with a small size.

[Means for Solving the Problems] An apparatus according to the present invention will be described with reference to the drawings. First
In the figure, the detection device detects a transmission position twice or more in one detection cycle with respect to one incident radiation (hereinafter referred to as twice detection, three times detection, and the like) to form a set of coordinates. This one
From the set coordinates and the known transmission position interval, a central processing unit (hereinafter referred to as a CPU) calculates a direction component from which the original radiation has flown. The intersection of the straight line having this directional component and the virtual projection plane at an arbitrary distance set in the CPU is calculated as the coordinates of the projection point. The above-mentioned projection points are calculated for each radiation from the subject, and these projection points are superimposed by an image display control device to form an image signal. A reconstructing apparatus comprising the above-mentioned device, wherein the image signal is displayed on a display device to be an image of a radiation source.

[Operation] If the coordinates of two points in space are determined by the geometry, the direction component of a straight line can be obtained, as well as detecting the transmission position of one radiation twice with detectors at known intervals. Then the direction of arrival of the original radiation can be determined. However, when the radiation dose is large, one detector may detect two or more transmission positions within a detection cycle, and it becomes impossible to determine each straight line. In such a case, the transmission position is detected three times for one radiation, and the straight line can be determined by going back and tracing the transmission position. Therefore, the transmission position of one radiation is detected two or more times in one detection cycle to form a set of coordinates.

A case of reconstructing an image of a radiation source by three detections based on the flowchart of FIG. 3 will be described.

The detection device is fixed on a tripod or the like toward the radiation source. Longer transmission position intervals increase the angular resolution, and enlarge the display to achieve telephoto. When the detection device is set to telephoto, the CPU adds the transmission position interval and enlarges the display screen. If the detection device is not telephoto, the CPU restores the transmission position interval and display. If there is any set of coordinate data from the detecting device that does not detect the transmission position even in one of the detectors, the CPU rejects the data and receives the next set of coordinate data. When each detector detects one or more transmissive positions in a set of coordinate data, a round robin is performed in the transmissive order, and the direction component of the straight line is obtained and stored. The virtual projection plane distance may be input in advance, but if not, it is newly input. The intersection of the virtual projection plane and the straight line having the above-described directional component is obtained, set as the coordinates of the projection point, and stored in the image display control device. The projection point is displayed on a display device.

The above-described arithmetic processing is performed until the end of the observation, and the projection points are displayed in a superimposed manner to obtain a reconstructed image of the radiation source. At this time, if the image is not blurred, the virtual projection plane distance may be changed until the image area is minimized.

As described above, the image of the radiation source is reconstructed by making the points of the subject and the image correspond one-to-one.

Embodiment FIG. 2 shows a first embodiment of the detection device. The detection device is surrounded by a lens barrel 1 for shielding radiation, and a light shielding film 2 and a fluorescent thin plate 3 are attached to an opening along a radiation axis. Depending on the type of radiation, the transmutation unit 4 is mounted before the fluorescent thin plate 3. The optical system 5 is mounted at a position where the fluorescent thin plate 3 is viewed obliquely, and forms an image of a fluorescent bright spot of the fluorescent thin plate 3 on the surface of the detector 6 due to radiation transmission. The light shielding film 12 and the fluorescent thin plate 13 are mounted again along the radiation axis. The optical system 15 is mounted at a position where the fluorescent thin plate 13 is viewed obliquely, and forms a fluorescent bright spot image of the fluorescent thin plate 13 by radiation transmission on the surface of the detector 16. Finally, along the radiation axis, the light shielding film 22
And the fluorescent thin plate 23 are attached. The optical system 25 mounts the fluorescent thin plate 23 at a position obliquely viewed and forms a fluorescent bright spot image of the fluorescent thin plate 23 on the surface of the detector 26 due to radiation transmission. Light shielding film 2, 12, 22
Is mounted in front of each fluorescent thin plate so that external light and the adjacent fluorescent thin plates 3, 13, and 23 do not affect each other. Attachments 7, 17 of known length can be attached and detached between the fluorescent thin plates 3 and 13 and between the fluorescent thin plates 13 and 23. Further, the optical systems 5, 15, and 25 can be a system for enlarging a part of the fluorescent thin plates 3, 13, and 23 and forming an image on the surfaces of the detectors 6, 16, and 26. The optical systems 5, 15, and 25 are optical systems using lenses, and the optical system 5 and the detector 6 are configured to detect a part of the fluorescent thin plate 3 in an enlarged manner.
The embodiment in which the detectors 16 and 26 detect the entire fluorescent thin plates 13 and 23 is illustrated. The transmutation unit 4 is detachable, and the fluorescent thin plates 3,13,23
Can be exchanged. In this way, the detectors 6, 16, and 26 detect the transmission position of one radiation.

The detection device configured as described above is fixed to a subject from which an image of a radiation source is to be obtained, for example, a specimen to which a radioactive element is administered as a tracer, a celestial body that emits radiation, or an area to be monitored. Radiation incident on the detection device at an arbitrary angle passes through the light shielding film 2 and is separated from visible light by the fluorescent thin plate 3.
And emits fluorescent bright spots.

As the fluorescent thin plate, CdWO ₄ , BGO or plastic scintillator, LiI or NaICsI to which Tl is added as an activation center for radiation, or LiI to which Eu is added is used. (Γ, β), (n, α), (n, β), and other transmutation reactions for radiation that is thin and difficult to emit light (eg, neutrons, X-rays, and γ-rays) The fluorescent thin plate 3 to which In, Li, B, Be or other elements are added, or convert the light into α-rays or β-rays by attaching the nuclear conversion part 4 containing these elements,
Can be transmitted, so that an image of the source can be obtained for various types of radiation. When converted to alpha rays, the range is only a few centimeters even in air, so it is used in a dilute atmosphere such as space.

The bright spot of the fluorescent thin plate 3 is imaged on the surface of the detector 6 by the optical system 5 and becomes the coordinates of the transmission position of radiation.

As the transmission position detector, a CCD, BBD, or other charge transfer element capable of detecting the position with a small amount of light, or a position detection type microchannel plate with a photocathode or another image converter is used. For example, in an astronomical CCD, the minimum number of photons that can be detected is about 200, and the number of pixels is
There are 640,000, the former one in the microchannel plate and the latter three million. On the other hand, the energy of radiation due to nuclear decay is in the range of 1.5 MeV to 8.8 MeV for α-rays on average 5.
4MeV, average of 1.06 MeV in the range of 3 keV to 10.4 MeV for β ^- ray,
The average is 0.6 MeV from 2.1 keV to 7.1 MeV for gamma rays. A 0.6 MeV gamma ray emits 115 photons per unit solid angle while losing energy in a plastic scintillator with an absolute fluorescence efficiency of 0.02. For 2.1keV γ-rays, NaI (T
During the loss of energy in l), seven photons are emitted per unit solid angle, and two photons are emitted per unit solid angle even when distributed to detection three times. Therefore, the detector 6 detects the bright spot position of the fluorescent thin plate 3 as the first transmission position of the radiation. When the image converter is a microchannel plate, even a few photons can be detected, so that low-energy radiation may be used.

When the radiation transmitted through the fluorescent thin plate 3 further emits fluorescence at the fluorescent thin plate 13, the detector 16 detects the radiation as the second transmission position of the radiation in the same manner as described above. The CPU calculates the flying direction for one radiation whose section distance between the fluorescent thin plates 3 and 13 is known and whose two transmission positions are known. However, when the radiation dose is large and the detectors 6 and 16 have respectively received two or more signals within the detection cycle, the flight direction of each line cannot be calculated. Therefore, the third transmission position for one radiation is detected by the detector 26 in the same manner as described above. Also in this case, the fluorescent thin plate 13
It is assumed that the section distance between and is known.

Before calculating the direction component, specify whether the detection data is wide-angle or telephoto. When attaching the attachments 7 and 17, or by enlarging a part of the fluorescent thin plates 3, 13 and 23, the detectors 6, 16 and
When imaging on 26 planes, it is telephoto. For example, to set the angular resolution of an image to 4 arcsec, a fluorescent thin plate of 6.1 mm square should be 12.2 m.
It is sufficient that an image is magnified and formed on a CCD surface of 800 × 800 pixels of m square and the length between the fluorescent thin plates 3 and 23 is set to about 39 cm. If the dose is small, the area of the fluorescent thin plate and the number of CCDs used per detector should be increased to increase the light receiving cross-sectional area. To obtain the same angular resolution, the X-ray oblique incidence reflection telescope takes about 3.4m,
Similarly, a coded mask imaging device having a small section having a diameter of 2.5 mm has a length of about 129 m.

In the case of a high dose that the detectors 6, 16, and 26 detect two or more points within the detection cycle, the CPU rounds the points detected by the detector 16 to one point detected by the detector 26 and detects One straight line is determined by examining the linearity with the points detected by the detector 6, and the direction of arrival of each radiation within the detection cycle and for all data can be calculated sequentially and repeatedly. This flying direction data is stored in an external storage device as a direction component of a certain straight line at a known distance between the fluorescent thin plates.

The data detected three times for one radiation becomes the target of the directional component calculation, and the one and two detection data such as high energy γ-rays transmitted through the lens barrel 1 from other than the angle of view are rejected. , The direction component can be determined.

Next, a virtual projection plane is set in the CPU at an arbitrary distance based on one of the fluorescent thin plates. The CPU calculates the intersection of the virtual projection plane at an arbitrary distance and the straight line having the directional component obtained above, sets the intersection as the coordinates of the projection point, and sends the coordinates to the image display control device. The display device projects the projection point.

The data of each direction component and the virtual projection plane are calculated in the same manner as described above, and each projection point is superimposed and displayed on the display device to be reconstructed as an image of the radiation source. At this time, if the contour is blurred, the virtual projection plane distance is set so that the area of the image is minimized.
Focusing can be performed by re-specifying to the CPU.
Even when the depth of field is large, the shape of the radiation source can be known by changing the projection plane distance. If the shape of the subject is known, the source distribution can be known in detail by programming the shape.

By attaching a Ge semiconductor or other spectrometry 9 at the end of the radiation axis, it is possible to know the nuclide of the radiation source from the energy spectrum and analyze the amount of energy absorption by the substance between the radiation source and the detection device as before. .

FIG. 4 shows a second embodiment of the detection apparatus, in which the detection is performed three times using concave mirrors in the optical systems 5 and 15. Since the detector 26 for the third detection is mounted on the radiation axis, it is a microchannel plate of a position detection type that can be operated with X-rays, γ-rays or ion beams. In this case, a photocathode is not required. Unlike the first embodiment, no spectrometry can be attached, but the size can be further reduced. Others are the same as the first embodiment.

FIG. 5 shows a third embodiment of the detecting device, in which the detecting mechanism in the middle of the second embodiment is omitted. Since the detection is performed twice, it is effective when the dose is low. Compared with the three detections, there are advantages that the detection device can be further reduced in size, and that the calculation capability and external storage capacity of the CPU can be reduced.

[Effect of the Invention] The device according to the present invention has the following effects.

(1) Source images are obtained for various types of radiation.

(2) The image can be reconstructed even at a low dose and regardless of the energy level.

(3) The depth of field and the object distance may be arbitrary.

(4) The detection mechanism is simple, and there is no need to mechanically scan the subject.

(5) Even if the detection device is small, high resolution can be obtained.

(6) Wide angle and telephoto functions can be easily provided.

(7) Since the calculation is a simple geometric operation, the processing time is short, and the CPU may be small.

[Brief description of the drawings]

1 is a configuration example of an image reconstructing device, FIG. 2 is a cross-sectional view of a first embodiment of a detecting device, FIG. 3 is a flowchart of the image reconstructing device, FIG. 4 and FIG. It is sectional drawing of a 2nd and 3rd Example. 12,22 ... Light shielding film, 13,23 ... Fluorescent thin plate, 15,25 ... Optical system, 16,26 ... Detector, 17 ... Attachment, 8,18 ... Attachment insertion part, 9 ... Spectro Metric.

Claims (1)

(57) [Claims] 1. A detecting device for detecting a two-dimensional transmission position two or more times in one detection cycle for one radiation to form a set of two-dimensional coordinates and a known transmission position interval. A central processing unit that calculates a directional component of the original radiation from the dimensional coordinates and the transmission position interval, calculates an intersection of a straight line having the directional component with an imaginary projection plane at an arbitrary distance, and sets the coordinates of the projection point; A radiation source image reconstructing apparatus comprising: an image display control device that superimposes a projection point of the above-described coordinates on radiation to form an image signal; and a display device that displays the image signal as an image of the radiation source.