JPS6183985A - scintillation detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a scintillation detector used in a ring-type ECT device (emission computed tomography device) for positrons or single photons.

(b) Conventional ring-type ECT devices are constructed by arranging a large number of radiation detectors in a ring shape, and the spatial resolution improves as the radiation detectors are made smaller and the arrangement density is increased. Incidentally, in the past, a scintillation detector consisting of a combination of one scintillator and one photomultiplier tube is usually used as a radiation detector. Therefore, the size of each scintillation detector is limited by the size of the photomultiplier tube, and there is a limit to how small it can be made. Furthermore, even if the ring-shaped array can be made smaller, the number of photomultiplier tubes in the entire ring-shaped array increases, resulting in an increase in cost.

(C) Objective The object of the present invention is to provide a scintillation detector with improved spatial resolution without increasing the number of photomultiplier tubes and therefore without increasing the price.

(D) Structure In the scintillation detector of the present invention, a large number of scintillators are arranged adjacent to each other, and a certain number of scintillators are optically coupled to each of a plurality of photomultiplier tubes. Then, the first pulse height discriminator detects that the output pulse of each photomultiplier tube falls within a predetermined high level window, and the second pulse height discriminator detects that the output pulse falls within a predetermined low level window. It is detected that the Optical crosstalk is prevented between scintillators coupled to the same photomultiplier tube, and optical crosstalk occurs between scintillators coupled to adjacent photomultiplier tubes. Which scintillator is determined by the combination of the output of the first pulse height discriminator connected to each photomultiplier tube and the output of the second pulse height discriminator connected to another photomultiplier tube adjacent to the photomultiplier tube? It is determined whether radiation has entered the area.

(E) Example t51 In the figure, a large number of scintillators 1 are arranged adjacent to each other in a ring shape, and three scintillators are optically coupled to one photomultiplier tube 5 via a light guide 4. There is. An optical shielding plate 2 is inserted between the scintillators 1 connected to the same photomultiplier tube 5 to prevent mutual light crosstalk.
An optical coupling surface 3 is formed between the scintillators 1 coupled to the child multiplier tube 5, so that crosstalk of light occurs between them. A main wave height discriminator 7 and a sub wave height discriminator 8 are connected to each photomultiplier tube 5 via an amplifier 6, respectively. These wave height discriminators 7.8 are for discriminating the wave height of the output pulse generated from the photomultiplier tube 5, and the main wave height discriminator 7 is for discriminating the wave height of the output pulse generated from the photomultiplier tube 5. The secondary wave height discriminator 8 generates an output when the wave height is in a window lower than that of the main wave height discriminator 7, as shown in FIG. 2(b). This high level window was defined corresponding to the light from the scintillator 1 coupled to each photomultiplier tube 5 via the light guide 4, and the low level window was coupled to the adjacent photomultiplier tube 5. scintillator 1
It is determined in response to crosstalk light from The output of the main wave height discriminator 7 is outputted via the gate circuit 10, but this gate circuit 10 opens only when there is no output from the AND circuit 9, allowing the signal to pass through, and the output is sent from the AND circuit 9. When there is a signal, close it to block the signal. A
The output of the main wave height discriminator 7 and the output of the adjacent sub-wave height discriminator 8 are input to the ND circuit 9.

Now, a and b of the scintillator 1 in FIG.

It is assumed that γ-rays are incident on the objects labeled c and d, respectively. First, when γ-rays are incident only on scintillator a, the scintillation light generated here is blocked by the optical shielding plate 2, so it does not leak to the adjacent scintillator b, etc., and all enters the photomultiplier tube 5 of A. . Therefore,
In this case, the wave height of the output pulse generated from the photomultiplier tube A will be large, so on the A side, the main wave height discriminator 7
An output is generated from the subwave height discriminator 8, but no output is generated from the subwave height discriminator 8. Also, at this time, since no light is incident on the photomultiplier tube 5 on the B side, the main and sub-wave height discriminators 7.
8 does not produce any output, so in this case, the AN on the A side
Since no output is generated from the D circuit 9, the output of the main wave height discriminator 7 on the A side passes through the gate circuit 10 as it is.

Next, if γ-rays are incident only on scintillator b,
The scintillation light generated here is blocked by the optical shielding plate 2, so it does not leak to the adjacent scintillator a, but leaks to the adjacent scintillator C. Therefore, the light enters the photomultiplier tube 5 of A, and the crosstalk light leaked to the scintillator C enters the photomultiplier tube B. Therefore, in this case, the wave height of the output pulse generated from the photomultiplier tube A becomes large, and therefore, on the A side, an output is generated from the main wave height discriminator 7, but no output is generated from the secondary wave height discriminator 8. Since crosstalk light is incident on the photomultiplier tube B, the main wave height discriminator 7 does not produce an output on the B side, but the auxiliary wave height discriminator 8 produces an output. Therefore, in this case, an output is generated from the ANDN0 circuit on the A side, and as a result, the gate circuit 10 on the A side enters the blocking state, so the output of the main wave height discriminator 7 on the A side is blocked by the gate circuit 10. Put it away.

When γ-rays are incident only on scintillator C, the scintillation light is blocked by optical shielding plate 2, so it does not leak to adjacent scintillator d, but it does not leak to adjacent scintillator B.
It leaks. Therefore, the light enters the photomultiplier tube B, and the crosstalk light leaked to the scintillator b enters the photomultiplier tube A. Therefore, in this case, the wave height of the output pulse generated from the photomultiplier tube B becomes large, and therefore, on the B side, an output is generated from the main wave height discriminator 7, but no output is generated from the auxiliary wave height discriminator 8; At this time, since crosstalk light is incident on the photomultiplier tube A, the main wave height discriminator 7 does not produce an output on the A side, but the auxiliary wave height discriminator 8 produces an output. Therefore, in this case, the output from the ANDN0 circuit on the B side is instantaneously generated, and as a result, the gate circuit 10 on the B side enters the blocking state, so the output of the main wave height discriminator 7 on the B side is blocked by the gate circuit 10. Put it away.

When γ-rays are incident only on the scintillator d, the scintillation light is blocked by the optical shielding plate 2, so that all of the scintillation light is incident on the photomultiplier tube B without leaking to the adjacent scintillator C or the like. Therefore, in this case, photomultiplier tube B
The wave height of the output pulse generated from the B side becomes large, and therefore, an output is generated from the main wave height discriminator 7 on the B side, but no output is generated from the secondary wave height discriminator 8.
゛Since no light is incident on the electron multiplier tube A, neither the main nor the auxiliary wave height discriminator 7, 8 produces an output on the A side.Therefore, in this case, no output is produced from the ANDN0 circuit on the B side, so The output of the main wave height discriminator 7 on the B side passes through the gate circuit 10 as it is.

In this way, by determining the combination of the outputs of the main and auxiliary wave height discriminators 7.8 connected to the photomultiplier tubes A and H,
When an output is generated from the gate circuit 10 on the A side, it means that γ rays have entered the scintillator a, and when an output is generated from the ANDN0 circuit on the A side, it means that γ rays have entered the scintillator b. When an output is generated from the ANDN0 circuit, it can be determined that γ-rays have entered the scintillator C, and when an output has been generated from the B-side gate circuit IO, it can be determined that γ-rays have entered the scintillator d.

In addition, as shown in FIG.
A number of scintillators 1 are optically coupled and photomultiplier tubes 5 are arranged in a ring shape in at least two layers, and γ-rays are incident not only in the circumferential direction of the ring-shaped arrangement but also in a direction perpendicular to the circumferential direction in the same manner as above. If the scintillator 1 is configured to identify which scintillator 1 has been used, an ECT image of a multilayer slice can be obtained.

In addition, 1. Although the scintillators 1 and photomultiplier tubes 5 are arranged in a ring shape in the above example, they can also be arranged in a polygonal or spherical shape.

(F) Effects According to the present invention, the size of the scintillator can be made small regardless of the size of the photomultiplier tube, so it is easy to increase the arrangement density of the scintillators and improve the spatial resolution. Furthermore, since the number of photomultiplier tubes can be reduced, the cost can be reduced.

[Brief explanation of the drawing]

Figure 1 is a block diagram of one embodiment of the present invention, Figures 2 (a) and (b) are time charts for explaining the operation of the pulse height discriminator, and Figure 3 is a schematic diagram of another embodiment. FIG.

Claims (1)

[Claims] (1) A large number of scintillators arranged adjacent to each other, a plurality of photomultiplier tubes to which a certain number of scintillators are optically coupled, and an output pulse of each photomultiplier tube. a first pulse height discriminator that generates an output by detecting that the wave height is within a predetermined high level window; A second wave height discriminator circuit detects that the photomultiplier tube is present and generates an output. Optical crosstalk is caused between the scintillators connected to the multiplier tube, and the output of the first pulse height discriminator connected to each photomultiplier tube is connected to the scintillator adjacent to the photomultiplier tube. A scintillation detector that determines which scintillator radiation has entered in combination with the output of a second pulse height discriminator connected to a photomultiplier tube.