JPH01141389A - Scintillation detector - Google Patents

Abstract

PURPOSE:To suppress the deterioration of a space resolution in the periphery of a visual field by arranging the scintillators whose scintillation attenuation characteristics are different, in two layers. CONSTITUTION:Scintillators 1 whose scintillation attenuation characteristics are different such as a GSO 11 and a BGO 12, etc., are arranged in two layers in the depth direction and brought to optical coupling. Except the surface which is brought to optical coupling to a photoelectric multiplier 2, the scintillator 1 is covered with a reflecting material 19. An output of the photoelectric multiplier 2 is divided into an output signal A for showing a scintillation generated in a shallow part and an output signal B of a deep part by a waveform analyzer 3, and sent to a simultaneous counting circuit 4. It is also allowed to form a radiation detecting unit by coupling plural photoelectric multipliers to plural scintillators by a light guide. In such a way, by executing simultaneous counting of the output A of one waveform analyzer and the output B of the other waveform analyzer, the deterioration of a space resolution in the periphery of a visual field of a position annihilation point can be suppressed.

Description

[Detailed description of the invention] [Industrial application field]

This invention is a ring type ECT (Emission C
The present invention relates to a scintillation detector suitable for a computed tomography (CT) device, and particularly to a scintillation detector suitable for a ring-type ECT device using a positron-emitting nuclide.

[Conventional technology]

In a ring-type ECT device, as shown in Fig. 4, usually 1
A large number of radiation detectors in which one photomultiplier tube 2 is optically coupled to one scintillator 1 are arranged in a ring shape. In addition,
The scintillator 1 is covered with a reflective material 19 that reflects light except for the surface optically coupled to the photomultiplier tube 2, so as to increase the incidence efficiency of scintillation light emission into the photomultiplier tube 2.

[Problems to be solved by the invention]

However, in such a detector that combines one scintillator and one photomultiplier tube, when radiation enters the scintillator and scintillation occurs,
There is a problem in that depthwise information about the depth of the scintillator at which the scintillation occurs cannot be obtained. Particularly, in the case of the ECT device, since information in the depth direction cannot be obtained in this way, a problem arises in that the spatial resolution becomes large at the periphery of the field of view. That is, the fourth
As shown in the figure, the positron disappears at point P, and two γ-rays are emitted in 180° different directions as shown by the solid line, one of which penetrates diagonally through one or more adjacent scintillators 1, and a certain scintillator If scintillation occurs in the deep part of 1, there is no information in the depth direction, so
Counting is performed assuming that the positron extinction point is located on the dotted line. Such an error (perpendicular distance of the dotted line from the solid line) becomes larger as the gamma rays are incident obliquely, so the spatial resolution deteriorates as the distance from the center increases, as shown in FIG. This invention is a ring-type ECT that can obtain information in the depth direction.
It is an object of the present invention to provide a scintillation detector that can suppress deterioration of spatial resolution around the field of view when applied to a device.

[Means to solve the problem]

A scintillation detector according to the present invention includes scintillators arranged in at least two layers in the depth direction, each having different scintillation attenuation characteristics, a photomultiplier tube optically coupled to the scintillator, and an output of the photomultiplier tube. It consists of a connected waveform analyzer.

[For production]

Since scintillators with different scintillation attenuation characteristics are arranged in at least two layers in the depth direction,
When radiation is incident and scintillation occurs, the decay time of the output pulse from the photomultiplier tube will differ depending on in which layer the scintillation occurs. Therefore, 1. By distinguishing the waveform of the output pulse of this photomultiplier tube with a waveform analyzer, it is possible to determine in which layer scintillation occurs, and to obtain information in the depth direction.

【Example】

In the embodiment shown in FIG. 1, the scintillation detector according to the present invention is applied to a positron ring type ECT device. In this figure, scintillator 1 is composed of scintillators arranged in two layers in the depth direction, each having different scintillation attenuation characteristics, such as G5011 and BG.
○ Consists of 12. These GSoll and BGO12 are optically coupled. A photomultiplier tube 2 is optically coupled to this scintillator 1. The scintillator 1 is a reflective material 1 that reflects light except for the surface optically coupled to the photomultiplier tube 2.
9 to increase the incidence efficiency of scintillation light emission into the photomultiplier tube 2. The output of the photomultiplier tube 2 is guided to a waveform analyzer 3, which outputs an output signal A indicating that scintillation emission has occurred in a shallow portion and an output signal B indicating that scintillation emission has occurred in a deep portion. These are sent to the coincidence counting circuit 4. For example, the positron disappears at point P, and two γ-rays are emitted in 180° different directions as shown by the solid line, one of which penetrates one or more adjacent scintillators 1 diagonally, and a certain scintillator 1. Suppose that scintillation occurs in a deep part. In this case, light emission will occur in the BGO 12, which is a deep scintillator layer. Incidentally, the attenuation characteristics regarding scintillation light emission of G5011 and BGO12 are greatly different as shown by curves a and b in FIG. 2. Therefore, by determining the waveform of the output pulse of the photomultiplier tube 2 with the waveform analyzer 3,
When scintillation occurs in the shallow layer GSoll, output A can be generated, and when scintillation occurs in the deep layer BGO 12, output B can be generated. Therefore, in this embodiment, by performing coincidence counting between the output A of one waveform analyzer 3 and the output B of the other waveform analyzer 3, the point P where the positron actually disappears is close to the solid line on which the point P is located. Simultaneous counting can be performed assuming that the positron vanishing point is on a straight line, and deterioration in spatial resolution can be suppressed. In addition, although the case where one photomultiplier tube 2 is optically coupled to one scintillator 1 has been described above, the case is not limited to this. Even when the tubes 2 are combined by the light guide 5 to form one radiation detection unit, the scintillator 1 is divided into a shallow layer scintillator 11 and a deep layer scintillator 12, each having different scintillation attenuation characteristics.
It can be applied by forming it with. in this case,
The above two-layer scintillator 1 is placed in the direction of the radiation incident surface.
16 scintillators are arranged optically separated from each other, and 4 photomultiplier tubes 2 are connected to these, and which scintillator 1
Discrimination of the position in the direction of the incident surface where light emission occurs is determined from the ratio of the output magnitudes of the respective photomultiplier tubes 2 using Anger's method. Information in the depth direction is obtained by waveform discrimination of the output pulse waveform of the photomultiplier tube 2. Of course, when forming one radiation detection unit by coupling a plurality of scintillators and a plurality of photomultiplier tubes with a light guide in this way, a configuration other than that shown in FIG. 3 may be used. Furthermore, in both Figures 1 and 3 above, the scintillator is made of two layers in the depth direction, but if the pulse waveforms are different,
It can also have three or more layers.

【Effect of the invention】

According to the scintillation detector of the present invention, information in the depth direction can be obtained with a simple configuration, and in particular, ring type E
When used as a radiation detector in a CT device, it is possible to reduce deterioration of spatial resolution around the field of view.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of one embodiment of the present invention, FIG. 2 is a graph showing the attenuation characteristics of each scintillator, FIG. 3 is a schematic diagram of another embodiment, FIG. 4 is a schematic diagram of a conventional example, and FIG. FIG. 5 is a graph showing the characteristics of conventional spatial resolution. 1...Scintillator, 11...G50112...
BG○, 19... Reflective material, 2... Photomultiplier tube, 3
... Waveform analyzer, 4... Coincidence circuit, 5... Light guide.

Claims (1)

[Claims] (1) scintillators arranged in at least two layers in the depth direction, each having different scintillation attenuation characteristics;
A scintillation detector comprising a photomultiplier tube optically coupled to the scintillator and a waveform analyzer connected to the output of the photomultiplier tube.