JPH0546512B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a radiation detector, and particularly to a ring-type ECT device (emission computer tomography device) that uses a single photon and a positron as a radionuclide. Concerning a suitable radiation detector.

(b) Prior art In ring-type ECT devices, a combination of one scintillator and one photomultiplier tube (hereinafter abbreviated as PMT) is normally used as a radiation detector. There is a problem that the spatial resolution cannot be increased because the size cannot be made very small. Furthermore, even if the PMTs can be made smaller, the number of PMTs will increase, causing problems in terms of manufacturing costs. This is especially a big problem in the type of camera that simultaneously images multiple slice planes.

Conventionally, when photographing three slice planes at the same time, one scintillator 6 is used as shown in FIG.
and one PMT7 are arranged in three sets in the Z direction (slice thickness direction), and a large number of these are arranged in the X direction to form a ring shape (that is, the X direction is the circumferential direction). A configuration is taken. The collimator 8 is used only in the case of a single photon, and is not used in the case of a positron. Here, the detector width d is mainly restricted by the geometric size of the PMT 7 and cannot be made smaller than a certain level, so the spatial resolution in the X direction cannot be increased, and therefore the spatial resolution of the image cannot be improved. I can't. Further, since the size is also limited in the Z direction, it is not possible to reduce the slice thickness.
Furthermore, even if it were possible to reduce the size of the PMT7, a large number of PMTs would be required because a large number of radiation detectors would be arranged in the circumferential direction and arranged in the slice thickness direction according to the number of slices.
It is inevitable that problems will arise in terms of manufacturing costs.

(c) Purpose This invention is a radiation therapy system that can improve the spatial resolution of images in each slice plane, reduce the slice thickness, and require fewer PMTs without causing manufacturing cost problems. The purpose is to provide a detector.

(D) Configuration In the radiation detector according to the present invention, a plurality of scintillators having a predetermined length in one direction are arranged in a direction substantially perpendicular to the length direction, and the length direction of the plural scintillators is arranged in a direction substantially perpendicular to the length direction. Each of the two ends has a plurality of mutually independent photodetection systems.
One or more PMTs are arranged, and the light output from one end is distributed to the photodetection system on the one end side by a light guide at a different ratio for each scintillator, and the light output from the other end is distributed to the light detection system on the one end side. The guide distributes the light to the light detection system at the other end at a different ratio for each scintillator, and which scintillator emit light is determined by the ratio of the output of each light detection system at one end and the other end. In addition to determining whether the light emission has occurred, the position in the length direction at which light emission has occurred is calculated based on the ratio of the output of the PMT on the one end side and the output of the PMT on the other end side.

(E) Example In FIG. 1, scintillators 1, 1, ... having a predetermined length in one direction (Z direction) are arranged in plural scintillators in a direction (X direction) substantially perpendicular to the length direction (Z direction). They are lined up. These scintillators 1,
1,... are each optically independent,
More desirably, a light reflecting material is applied between the scintillators 1, 1, . A PMT is installed at each end of the plurality of scintillators 1, 1... in the Z direction.
3, 3 are arranged via light guides 2, 2. The PMTs 3, 3 each have two mutually independent photodetection systems 3A, 3B and 3C, 3D, and are so-called two-circuit built-in type. Here 2
One PMT with built-in circuit is used, but 1
Two PMTs may be placed in each circuit. The light guides 2, 2 at both ends are optically independent 2
It consists of two light guides 2A, 2B and 2C, 2D. The light output from one end of the scintillators 1, 1, .
It is distributed to input surfaces A and 3B. In addition, the light output from the other ends of the scintillators 1, 1, ... is distributed to the input surfaces of the light detection systems 3C and 3D on the other end side by the light guides 2C and 2D at different ratios for each scintillator. It's getting old.

That is, one output surface of scintillators 1, 1, ... is represented by rectangles 11, 12, 13, 14,
The input surface of PMT3 is represented by rectangles 15, 16, 17, and 18, and the input surface of optical system 3A is represented by rectangles 15, 16, 17, and 18.
When the input surface of the optical system 3B is represented by rectangles 17, 18, 19, and 21 with rectangles 16, 21, and 19,
The light guide 2A is a triangular column 11, 12, 13, 1
Part of 5, 16, 17, i.e. 13, 17, 20,
The light guide 2B has a shape in which the tetrahedral part of No. 21 is removed, and the light guide 2B is made of triangular prisms 11, 13,
14, 15, 17, 18 as tetrahedron 11, 15, 1
It has a shape where only parts 9 and 20 have been removed,
The more the scintillators 1, 1, ... are on the left side of the diagram, the more the amount of light distributed to the input surface of the optical system 3A becomes greater than the amount of light distributed to the input surface of the optical system 3B, and the more the scintillators 1 on the right side of the diagram The distribution ratio of the amount of light is determined so that the amount of light distributed to the input surface of the optical system 3A is smaller than the amount of light distributed to the input surface of the optical system 3B. In addition, the other output surface 31,
The same applies to the light guides 2 attached to the light guides 32, 33, and 34, which are two optically independent light guides 2C and 2D. The light guide 2C has triangular pillars 31, 32, 34, 35, 36,
38, with the tetrahedrons 34, 38, 39, and 40 removed, and the light guide 2
D is triangular prism 32, 33, 34, 36, 37, 38
It has a shape that looks like the tetrahedrons 32, 36, 40, and 41 have been removed. The left side of the diagram of a large number of scintillators 1, 1, etc., the more the optical system 3D
The amount of light distributed to the input surface of optical system 3D is greater than the amount of light distributed to the input surface of optical system 3C. The distribution ratio of the amount of light is determined so that it is less than the amount of light to be distributed.

The collimator 4 is used when the radionuclide is a single photon. A large number of radiation detectors configured in this manner are arranged in a ring shape in the arrangement direction of the scintillators 1, 1, . . ., that is, in the X direction. That is, the X direction is the circumferential direction, and the Z direction is the slice thickness direction.

The outputs A to D of the photodetection systems 3A to 3D are then sent to adders/subtracters 51 and 52 and an adder 53 as shown in FIG.
+
B)-(C+D)} and (A+B+C+D) are obtained. Since the light distribution ratio is determined by the light guides 2A to 2D as described above, {(B+
C)-(D+A)} corresponds to which scintillator 1 generates light emission, that is, the position of the light emission in the X direction. Also, {(A+B)-(C+D)} indicates which side of both lengthwise ends of the scintillator 1 a greater amount of light has reached, so it corresponds to the position of light emission in the Z direction. Furthermore, (A+B+C+
D) is an output corresponding to the energy of the radiation incident on the scintillator 1. Therefore, the divider 54,
55 and normalize with the energy signal to obtain {(B+C)-(D+A)}/(A+B+C+D) {(A+B)-(C+D)}/(A+B+C+D), the former is the X direction position. The latter becomes a position signal indicating the Z-direction position.

In this way, although there are four photodetection systems 3A to 3D, it is possible to determine which of the thin scintillators 1 the radiation has entered, and it is possible to detect radiation in the X direction without being restricted by the geometric size of the PMTs 3, 3. The spatial resolution of the image is increased, thereby increasing the spatial resolution of the image. In addition, since it is not necessary to provide PMT3 corresponding to the number of thin scintillators 1, PMT3
The number of objects can be reduced. Furthermore, since the position can also be determined in the Z direction, images of thin multi-layered slice planes can be captured simultaneously without using PMT corresponding to the number of layers. It is no longer necessary to form a PMT ring-shaped array for the number of layers corresponding to the number of layers.
In this respect as well, the number of PMT3 can be reduced.

Note that the above position calculation is just one example, and the X-direction position and Z-direction position can also be determined using an analog position calculation circuit such as that used in a scintillation camera. In addition, in the above, the PMTs 3, 3 are provided only at both lengthwise ends of the scintillator 1, but multiple PMTs are also arranged on the side opposite to the radiation incident side, that is, on the upper side in the figure, and the Z including their outputs is If the position calculation in the direction is performed, the position resolution in the Z direction will be improved.
Furthermore, if the energy signal is determined by including these outputs, the energy resolution will also be improved.

(f) Effects According to the present invention, the spatial resolution of images can be improved without increasing the number of PMTs, thereby suppressing manufacturing costs, and the slice thickness can be reduced to increase the number of slice plane layers that can be simultaneously imaged. I can do a lot.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of an embodiment of the present invention, FIG. 2 is a block diagram of a signal system of the same embodiment, and FIG. 3 is a schematic perspective view of a conventional example. 1, 6...scintillator, 2...light guide,
3, 7...PMT, 4, 8...collimator.

Claims (1)

[Claims] 1 A plurality of scintillators having a predetermined length in one direction and arranged in a direction substantially perpendicular to the length direction, and a plurality of scintillators arranged at one end in the length direction of the plurality of scintillators. one or more photomultiplier tubes having mutually independent photodetection systems;
A light guide that distributes the light output from one end to the photodetection system at a different ratio for each scintillator, and a plurality of mutually independent photodetectors arranged at the other end in the length direction of the plurality of scintillators. one or more photomultiplier tubes having a photomultiplier system, a light guide that distributes light output from the other end to the photodetection system at a different ratio for each scintillator, and one or more photomultiplier tubes having one or more photomultiplier tubes on the one end side and the other end side. A circuit that determines which scintillator generates light emission based on the ratio of the outputs of each photodetection system, and a circuit that determines the length of the scintillator based on the ratio of the output of the photomultiplier tube on one end and the output of the photomultiplier tube on the other end. A radiation detector consisting of a circuit that calculates where in the horizontal direction light emission occurs.