JPH0690290B2 - Radiation detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an RI (single photon or positron emission type) which is administered in a subject with a large number of radiation detectors arranged in a ring around the subject. The present invention relates to a radiation detector suitable for a ring-type ECT device (emission computed tomography device) that detects radiation (γ-rays) from a radioisotope) and obtains an RI distribution image inside a subject.

In the conventional single photon or positron ECT device, one photomultiplier tube (hereinafter abbreviated as PMT) (42) is optically coupled to one scintillator (41) as shown in FIG. This radiation detector was used and many of these detectors were arranged in a ring type.

In the figure, (43) is a light guide that optically couples the scintillator (41) and PMT (42).

Problems to be Solved by the Invention Therefore, the radiation detector as a whole cannot be downsized because there is a limit to how small the PMT can be, and the position resolution is limited. Even if radiation detection can be miniaturized by combining a small scintillator and a small PMT in order to improve the position resolution, arranging them in a ring type increases the number of PMTs, and the associated circuits are complicated. Therefore, there is a problem that the manufacturing cost of the entire device is increased.

This invention has a very high position resolution and requires a small number of PMTs, and radiation detectors are arranged in a ring shape.
An object is to provide an inexpensive radiation detector suitable for application to an ECT device.

A radiation detector according to the present invention comprises a single photomultiplier tube and a plurality of scintillator elements optically coupled to the front surface thereof and having different thicknesses in the radiation incident direction. The scintillator blocks are optically separated and arranged, and the scintillator element on which the radiation is incident is discriminated based on the wave height analysis result of the output signal of the photomultiplier tube.

Action Since scintillator elements with different thicknesses are arranged in front of the PMT, when light is emitted by the incidence of radiation, the amount of light reaching the PMT from each scintillator element is different, resulting in a difference in the peak value of the energy spectrum. Therefore, since the output signal of the PMT differs depending on the scintillator element on which the radiation is incident, the scintillator element of the scintillator block can be discriminated to which scintillator element of the scintillator block by which the radiation is incident.

Example In FIG. 1, (1A) and (1B) are thin scintillator elements whose thickness in the radiation incident direction is different from L _A and L _B, and both scintillator elements (1A) and (1B) are the radiation incident surface (lower side in the figure). The scintillator blocks (1) are formed by arranging the scintillator blocks (1) in one direction so that they are on the same plane.

Light reflection material (2) between each scintillator element (1A) (1B)
Are optically isolated from each other so that there is no crosstalk of light.

The output surface (upper surface in the figure) of the scintillator block (1) is optically coupled to the PMT (4) via the light guide (3).

The light guide (3) is made of a transparent material such as glass or arrill, which absorbs less light at the emission wavelength of the scintillator block (1). As shown in the figure, the scintillator element (1A)
It is formed stepwise to compensate for the thickness difference of (1B).
In order to improve the light collection efficiency, it is desirable that the scintillator elements (1A) and (1B) are coated with a light-reflecting material except for the joint interface between the two, except for the output surface facing the PMT.

With the above configuration, when radiation (γ-rays) is uniformly incident on the scintillator block (1), that is, the scintillator elements (1A) and (1B) from below in the figure, the light emitted from the scintillator element (1A) emits light at the solid angle Ω _A at PMT (4 ) And the light emitted from the scintillator element (1B) reaches the PMT (4) at the solid angle Ω _B.

In the figure, since the solid angle is Ω _A > Ω _B , the signals corresponding to the scintillator elements (1A) and (1B) have different peak values as shown in the energy spectrum diagram of FIG. The actual detector signal is a superposition of both spectra.

Here, the peak value of the energy spectrum in Fig. 2 is PMT.
It is determined by the angle of incidence on (4) and the thickness of the scintillator (the angle of incidence contributes to the crest value more than the thickness of the scintillator), and the crest value moves to the high energy side or the low energy side.

Therefore, it is possible to determine which of the scintillator elements (1A) and (1B) the radiation has entered by performing a pulse height analysis on the output signal of the PMT (4).

Therefore, as shown in FIG. 3, the output signal of the PMT (4) is guided to the wave height analyzers (5A) and (5B). Second on the wave height analyzer (5A)
Set the window W _A corresponding to the crest value P _A of the scintillator element (1A) and the window W _B corresponding to the crest value P _B of the scintillator element (1B) in the crest analyzer (5B). For example, the scintillator element on which the radiation is incident can be identified from the output.

In the embodiment, the scintillator block is composed of two scintillator elements having different thicknesses, but it may be three or more.

Further, the PMT wave height analyzing means is used in combination with the single channel wave height analyzer, but a multi-channel wave height analyzer may be used. Furthermore, the scintillator block was formed by arranging the independent scintillator elements with different thicknesses in a row, but one scintillator plate with different thickness was formed in the direction perpendicular to the radiation incident direction, and the scintillator block was formed at the boundary with different thickness. You may form a scintillator block by providing a notch in a radiation incident direction. In this case, crosstalk can be prevented more effectively by filling the inside of the cut with a light reflecting material.

EFFECTS OF THE INVENTION According to the present invention, the scintillator element on which the radiation of the scintillator block is incident can be identified with a small PMT, and the cost of the ring-type ECT device can be reduced.

In addition, the scintillator elements that make up the scintillator block can be made smaller without being limited by the size of the PMT, and the spatial resolution can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention, and FIG.
2 is an energy spectrum diagram for explaining the operation principle of FIG. 2, FIG. 3 is a block diagram showing the circuit of the embodiment of FIG. 1, and FIG. 4 is a perspective view showing the configuration of a conventional example. 1: Scintillator block 1A, 1B: Scintillator element 2: Light reflector, 3: Light guide 4: PMT, 5A, 5B: Wave height analyzer

Claims (3)

[Claims] 1. A scintillator block in which a plurality of scintillator elements having different thicknesses in a radiation incident direction are optically separated from each other and arranged, and a photomultiplier tube optically coupled to an output surface of the scintillator block. The radiation detector characterized in that the scintillator element on which the radiation of the scintillator block is incident is discriminated based on the wave height analysis result of the output signal of the photomultiplier tube. 2. The radiation detector according to claim 1, wherein the radiation input surfaces of the scintillator element are located on the same plane. 3. The radiation detector according to claim 1, wherein the scintillator block and the photomultiplier tube are optically coupled via a light guide.