JPH06273529A - Detector for positron tomographic apparatus - Google Patents

Abstract

PURPOSE:To provide a detector for positron tomographic apparatus in which positional error, so-called parallax error, can be reduced while preventirxg the structure of detector from being complicated or enlarged. CONSTITUTION:Rectangular, porous, planar converters 60 for converting gamma-rays incident vertically from above into electrons are arranged vertically and semiconductor position detecting elements 61 for detecting the position in x-direction at the time of conversion of gamma-rays are applied to the opposite sides of the porous converter 60. The detectors 61 detect the position in z-direction at the time of conversion of gamma-rays thus reducing parallax error due to gamma-rays impinging obliquely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector for a positron tomography apparatus equipped with a converter for directly converting γ rays into electrons.

[0002]

2. Description of the Related Art Conventional radiation detectors for directly converting γ-rays into electrons and detecting the converted electrons are disclosed in JP-A-59-65783, 60-135884, and 63-40.
5 and 6 in addition to the one disclosed in Japanese Patent No. 381.
Those shown in are known.

The conventional radiation detector shown in FIG. 5 includes a microchannel plate (hereinafter referred to as MCP) 1 which is radiation / electron converting means and an MC which is electron multiplying means.
P2 is laminated, and the plurality of laminated MCPs 1 and 2 are superposed on the reading electrode 3.

The above MCPs 1 and 2 are made up of many tens of thousands of hollow high lead glass tubes (inner diameter 10 to 50 μm).
From m), they have the same size and shape, and the peripheral surface of each high-lead glass tube functions as an electron emitter or a secondary electron emitter.

The MCP1 located at the uppermost position has a planar rectangular shape and has a function of a converter for converting γ-rays incident from above into electrons and emitting the electrons, and is mounted horizontally on the MCP2. There is. The MCP2 has a function of multiplying the electrons emitted from the MCP1 by an electron, and the reading electrode 3
It is placed horizontally on top.

A position detection type electrode (for example, a cross-wired anode type) is adopted as the readout electrode 3, and the readout electrode 3 has the same size and shape as the MCPs 1 and 2 and is electron-multiplied. It has a function of detecting incident positions of a plurality of electrons.

However, the γ-rays vertically fall from the upper MCP to the lower MCP.
When incident on 1, the MCP 1 converts the γ-rays into electrons and emits them, and the emitted electrons are electron-multiplied by the MCP 2, and the plurality of electron-multiplied electrons enter the reading electrode 3 and enter. The position is detected.

On the other hand, in another conventional radiation detector shown in FIG. 6, a gas 4 such as argon gas is enclosed in a porous laminated lead plate 5 which is a converter having a laminated structure, and this porous laminated lead plate 5 is used as a reading electrode 3. I try to layer it horizontally.

However, when γ-rays enter the porous laminated lead plate 5 vertically downward from above, recoil electrons are emitted from the porous laminated lead plate 5 in the ionization chamber (not shown), and the emitted electrons are enclosed. The gas 4 is ionized, and electrons are multiplied by an avalanche, and a plurality of the electrons thus multiplied enter the reading electrode 3 to detect the incident position.

[0010]

By the way, the radiation detector described above is widely used for γ-ray measurement and the like. However, when it is applied to a positron tomography apparatus, the readout electrode 3 is used for radiation / radiation. Since it is arranged horizontally with respect to the electron converting means and the electron multiplying means, when the radiation enters from a direction obliquely inclined from the vertical direction, a parallax error (Paral error) is generated.
There is a drawback that a position error called "lux error" occurs.

Therefore, when the radiation is obliquely incident, the resolution around the visual field is deteriorated, and uniform high resolution cannot be expected in the visual field.

Further, the conventional radiation detector basically has a converter section (radiation / electron conversion), an electron multiplication section,
In addition, since the three constituent elements of the reading electrode section and the reading electrode section are indispensable, there is a drawback that the structure becomes complicated.

Further, in order to improve the detection efficiency of γ-rays, it is necessary to increase the probability of interaction with γ-rays. Therefore, the converter may be thickened or the converters may be laminated in many layers. Inevitably, there was a big problem that the detector became complicated and large.

The present invention has been made in view of the above, and is for a positron tomography apparatus capable of reducing a positional error called a parallax error and preventing the detector structure from becoming complicated and large. The purpose is to provide a detector.

[0015]

In the present invention, in order to achieve the above-mentioned object, a conversion which is composed of a flat plate-like member which converts incident radiation into electrons and which emits converted conversion electrons in a plane direction. Means and semiconductor position detecting means for superimposing in the plane direction of the converting means and detecting a position in two directions orthogonal to the superimposing direction into which the conversion electrons are incident, the two directions at the time of conversion of the radiation. Is detected by the position signal output of the semiconductor position detecting means.

In order to achieve the above object in the present invention, a plurality of detectors for a positron tomography apparatus according to claim 1 are arranged in parallel in the stacking direction, and the position of the stacking direction at the time of conversion of radiation is set. The detection is made based on the presence or absence of the output of each of the plurality of semiconductor position detecting means.

[0017]

According to the present invention, by vertically combining a single conversion means and a pair of semiconductor position detection means, it is possible to obtain position information in the x direction and position information in the z direction when converting radiation. Therefore, it is possible to prevent the occurrence of a positional error called a parallax error, and it can be expected that the deterioration of the resolution in the periphery of the visual field is reduced and a uniform high resolution is obtained. Further, it is possible to prevent the detector for the positron tomography apparatus from becoming complicated and large in size.

Further, according to the present invention, since the plurality of detectors for the positron tomography apparatus are arranged in parallel in the y direction, it is possible to detect the position in the y direction when converting the radiation by the semiconductor position detecting means. Becomes

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to an embodiment shown in FIGS.

The positron tomography apparatus described in this embodiment is different from the positron emission tomography apparatus in that a drug labeled with positron emission is administered to an object to be detected such as a living body and the r-line is in the opposite direction when the emitted positron disappears. Focusing on the fact that they are simultaneously emitted, it is a device that detects these simultaneously and reconstructs an image.

Therefore, detecting the γ-rays with high positional accuracy brings about a high resolution of the tomographic image of the reconstructed living body.

As shown in FIG. 1, the detector 6 for a positron tomography apparatus according to the present invention superimposes a pair of semiconductor position detecting elements (for example, a two-dimensional PSD) 61 on a porous converter 60 to convert γ-ray electrons into electrons. X-direction position during conversion, z
The semiconductor position detecting element 61 detects the directional position (depth position) to reduce the parallax error.

The porous converter 60 for converting γ-rays (radiation) indicated by an arrow into electrons is, as shown in FIG. 1 and FIG.
It is made of a metal such as lead having a large atomic number into a flat rectangular shape, and a large number of holes 60a are horizontally formed, and the large number of holes 60a are vertically aligned.

When γ-rays are converted into electrons by the lead atoms forming the porous converter 60, the electrons are emitted to the outside of the porous converter 60 through the numerous holes 60a.

The porous converter 60 made of lead is
Similar to MCP, it has the function of converting γ rays into electrons.
The probability of emitting electrons due to the interaction with γ rays is MCP2.
Since it is higher than that of MCP, it has a feature that it is more advantageous than MCP based on glass.

Further, unlike the conventional example, the porous converter 60 is sandwiched by a pair of semiconductor position detecting elements 61 in a vertically arranged state, and in other words, in a direction orthogonal to the direction in which a large number of holes 60a are formed. For example, γ rays are incident from above vertically.

However, with the vertical arrangement of the porous converter 60, the passage distance of γ-rays inside the porous converter 60 is extended, the probability of interaction between the γ-rays and the porous converter 60 is increased, and detection is performed. The sensitivity will be improved.

Then, the pair of semiconductor position detecting elements 6
The reference numeral 1 denotes, for example, a PSD in which a high resistance light receiving layer is formed on the surface of a semiconductor substrate by adding impurities, and a position signal electrode for extracting a photocurrent is provided on the end surface of the light receiving layer. They are stacked vertically in a state of being arranged vertically, and have a function of detecting the positions in the x direction and the z direction when converting γ rays.

That is, when γ-rays are incident on the porous converter 60 below from vertically above, high-speed electrons (recoil electrons) are emitted toward the semiconductor position detecting element 61 due to the interaction between γ-rays and lead.

When this high-speed electron passes through the light receiving portion of the adjacent semiconductor position detecting element 61 or stops in the light receiving portion of the semiconductor position detecting element 61, a large number of electron-hole pairs (carriers) follow the track. Is generated.

The carrier groups thus generated are collected by the position signal electrodes provided in the semiconductor position detecting element 61 and output as signals as shown by the arrows in FIGS. 1 and 2.

According to the above construction, by vertically combining the single porous converter 60 and the pair of semiconductor position detecting elements 61, the position information in the x direction and the position information in the z direction (depth) at the time of conversion of γ-rays. Information) and can be obtained.

However, if the position information for γ-ray detection is obtained, as shown in FIG. 3, it is possible to prevent the occurrence of a position error called a parallax error. You can expect the acquisition of resolution.

That is, as shown in FIG. 3, a positional error called a parallax error occurs when γ-rays are obliquely incident on the detector 6 for a positron tomography apparatus and interact (electron emission) at positions A and B. These are generated as a result of detecting the two different positions, in other words, γ rays having the same incident position and direction, but different incident positions.

The parallax error at this time is represented by Δ in FIG. In this case, if the positional information z in the depth direction where the interaction occurs can be obtained, this parallax error can be removed.

Further, according to the above structure, in the semiconductor position detecting element 61, the energy (ionization energy) required to generate a pair of electron-hole pairs is as small as about 3.6 eV in silicon, so that the high-speed electron from the porous converter 60 is used. A large number of electron carriers can be generated from the energy of.

Therefore, it is not necessary to provide a mechanism for performing electron multiplication, and the detector 6 for the positron tomography apparatus can be downsized.

Further, according to the above configuration, since the porous converter 60 is arranged in the vertical direction, the porous converter 6
The passage distance of γ rays inside 0 can be extended, and the probability of interaction between γ rays and the porous converter 60 can be increased.

Therefore, in order to improve the detection efficiency of γ rays,
It is possible to eliminate the need to thicken the converter and stack the converter in multiple layers, and prevent the detector from becoming complicated and large.

Next, FIG. 4 shows another embodiment of the present invention. In this case, a plurality of positron tomography detectors 6 described in the above embodiment are arranged in the lateral y direction. The semiconductor position detecting elements 61 are arranged side by side and detect the position in the y direction during the conversion of γ rays. Other parts are the same as those in the above embodiment.

According to this embodiment, x · z at the time of converting γ rays
The position information of the direction can be detected from the position signal output of the semiconductor position detecting element 61, and by knowing from which semiconductor position detecting element 61 the output is obtained, y of the γ-ray is detected.
Obviously, position information in the direction can also be obtained.

In this embodiment, a plurality of detectors 6 for positron tomography apparatus are simply arranged in parallel in the y direction which is the lateral direction, but the present invention is not limited to this, and a plurality of detectors 6 arranged in parallel are provided. The detector 6 for a positron tomography apparatus may be tilted in the vertical direction to further increase the probability of the interaction between the γ-rays and the porous converter 60.

Further, in the above-mentioned embodiments, the porous converter 6 is used.
Although the one using 0 is shown, it is not limited to this as long as it has the same function as the porous converter 60.

[0044]

As described above, according to the present invention, since it is possible to obtain the radiation detection position information in the z direction,
It is possible to prevent the occurrence of a position error called a parallax error, and through this prevention, it is possible to expect a reduction in resolution deterioration around the visual field and an even higher resolution.

Further, since it is not necessary to provide a mechanism for carrying out electron multiplication, there is a special effect that the detector for the positron tomography apparatus can be remarkably downsized.

Since the constituent elements of the detector for the positron tomography apparatus can be greatly reduced, it is possible to expect that the structure of the detector for the positron tomography apparatus can be surely prevented from becoming complicated. There is.

Furthermore, in order to improve the radiation detection efficiency,
It is possible to reliably eliminate the need to thicken the converter or stack the converter in multiple layers, and it is possible to reliably prevent the detector for the positron tomography apparatus from becoming complicated and large. Can be expected.

Further, according to the present invention, there is a remarkable effect that not only the position information of the radiation in the x direction and the z direction but also the position information in the y direction can be easily obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a detector for a positron tomography apparatus according to the present invention.

FIG. 2 is a sectional explanatory view showing an embodiment of a detector for a positron tomography apparatus according to the present invention.

FIG. 3 is an explanatory diagram illustrating a parallax error of a detector for a positron tomography apparatus according to the present invention.

FIG. 4 is a perspective view showing another embodiment of the detector for a positron tomography apparatus according to the present invention.

FIG. 5 is a perspective view showing a conventional radiation detector.

FIG. 6 is a perspective view showing another conventional radiation detector.

[Explanation of symbols]

6 ... Detector for positron tomography apparatus, 60 ... Porous converter (converting means), 61 ... Semiconductor position detecting element (semiconductor position detecting means).

Claims (2)

[Claims] 1. A conversion means that is composed of a flat plate-shaped member that converts incident radiation into electrons and emits converted conversion electrons in a plane direction, and conversion means provided by superposing in the plane direction of the conversion means. A semiconductor position detecting means for detecting a position in two directions orthogonal to the overlapping direction of incidence of electrons, and detecting the position in the two directions at the time of conversion of the radiation by a position signal output of the semiconductor position detecting means. Characteristic positron tomography detector. 2. A plurality of detectors for the positron tomography apparatus according to claim 1 are arranged in parallel in the stacking direction, and the position in the stacking direction at the time of conversion of radiation is output by each of the plurality of semiconductor position detecting means. A detector for a positron tomography apparatus, characterized by being detected by.