JPH07311270A - Radioactive ray detector - Google Patents

Abstract

PURPOSE:To provide a radioactive ray detector in which the space resolution of a positron emission tomography(PET) attached with a radioactive ray detector is improved and its sensitivity is not lowered. CONSTITUTION:Sixty-four scintillators 111-1188 are brought into close contact with each other and coupled to form a scintillator group 1. An APD array 2 having sixty-eight avalanche photodiodes(APD) 211-288 correspondingly one by one is optically coupled to the scintillators 111-188. Gamma rays gamma incident to the group 1 are emitted by the scintillator responsive to the incident position, the emitted light is diffused in the circumferential scintillator, and its light quantity is detected by the APDs 211-288 of the array 2. The detected data detected by the APDs 211-288 and photoelectrically converted are applied to an incident position calculator 3, the center of the gravity of the light quantity distribution is obtained based on the detected data to obtain the incident position of the gamma rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects radiation (gamma rays) emitted from a radioisotope (RI) that is administered to a subject and accumulated in a region of interest, and obtains a tomographic image of the RI distribution of the region of interest. The present invention relates to a radiation detector used in an apparatus for obtaining the same, for example, a positron emission tomography (PET) apparatus.

[0002]

2. Description of the Related Art In a conventional radiation detector of this type, a plurality of scintillators and a smaller number of photomultiplier tubes (PMTs) are optically coupled to each other and a reflector or the like is provided between the scintillators. , PM emission from scintillator
It is configured to be appropriately distributed to T and to determine the incident position of the gamma ray from the output ratio of each PMT.

As such a radiation detector, for example,
There are those disclosed in Japanese Patent Publication No. 62-500957 and Japanese Patent Laid-Open No. 5-281362. In the radiation detector disclosed in Japanese Patent Publication No. 62-500957, the length of the reflector provided between the scintillators is changed, and in JP-A-5-281362, the area of the reflector provided between the scintillators is changed. ing.

In recent years, a radiation detector using an APD array in which avalanche photodiodes (APD) are two-dimensionally arranged has been developed. In this radiation detector, a plurality of scintillators are provided on the entire surface of each boundary surface, and each scintillator is optically shielded to form a scintillator group. Each scintillator and APD are in a one-to-one correspondence.
So that the scintillator group and the APD array are optically coupled. In this radiation detector, for example, when an incident gamma ray is emitted by a scintillator, the light is shielded by a reflector between the scintillators, so that the emitted light is not dispersed to other scintillators and only the APD corresponding to the scintillator is scattered. The amount of light is detected by, and the incident position of the gamma ray is detected by the position of the APD where the amount of light is detected.

[0005]

However, the conventional example having such a structure has the following problems. The conventional radiation detectors have the following problems due to the provision of the reflector between the scintillators.

That is, PET having a radiation detector attached
In order to improve the spatial resolution of the device, it is necessary to make the scintillator small. On the other hand, in the conventional device, when the thickness of the reflecting material is made thin, the light emission passes through the reflecting material, and as a result, the accuracy of detecting the incident position is lowered. Therefore, in the conventional device, barium sulfate (BaSO 4 _When using ₄ ), the thickness must be above a certain level (for example, 0.15 mm).
Therefore, if the scintillator is made small in order to improve the spatial resolution of the PET apparatus, the volume of the reflecting material becomes large with respect to the volume of the entire radiation detector. As a result, the packing fraction (PF: volume of the scintillator itself / volume of the entire radiation detector). ) Becomes smaller. However, since the sensitivity of the PET apparatus is generally proportional to the square of PF, the sensitivity of the conventional apparatus is lowered in order to improve the spatial resolution of the PET apparatus.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a radiation detector that improves the spatial resolution of a PET apparatus equipped with a radiation detector and does not reduce the sensitivity thereof. To aim.

[0008]

The present invention has the following constitution in order to achieve such an object. That is, the present invention is a radiation detector that optically couples a plurality of scintillators two-dimensionally coupled to each other and an optical sensor to the scintillator group, and detects an incident position of a gamma ray incident on the scintillator group. While forming a scintillator group by bonding the scintillators to each other in close contact or close to each other, optically couple a plurality of photosensors to the scintillator group, and based on the detected light amount detected by each photosensor An incident position calculation means for detecting the incident position of the gamma ray by obtaining the center of gravity of the light amount distribution is provided.

[0009]

The operation of the present invention is as follows. The light emitted from the scintillator is diffused to each scintillator, and a plurality of optical sensors coupled to the scintillator group detect the amount of light according to the dispersion. The incident position calculation means finds the center of gravity of the light amount distribution based on the detected light amount detected by each optical sensor, and detects the light emitting position, that is, the gamma ray incident position.

Therefore, it is not necessary to provide a reflecting material between the scintillators, and the scintillator can be made small without making the PF small.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a perspective view showing a configuration of a radiation detector according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG.

In this embodiment, a total of 64 scintillators 1 _ij (i = 1 to 8, j), eight in the X direction and eight in the Y direction.
= 1 to 8) form a scintillator group 1 by providing a reflective material and closely contacting each other without forming a gap. As each scintillator 1 _ij , Bi ₄ Ge ₃
O ₁₂ (BGO), Gd ₂ SiO ₅ (GSO), NaI,
Inorganic crystals such as BaF ₂ and CsF are used. Also,
The surface of each scintillator scintillator 1 _ij is preferably mirror-finished.

[0013] The surface of each scintillator 1 _ij gamma ray γ enters (in the figure, the lower surface) (in the figure, upper surface) faces the opposite side, the one-to-one correspondence to each scintillator 1 _ij 64
A consisting of one APD2 _kl (k = 1-8, l = 1-8)
The PD array 2 is optically coupled with an adhesive or the like. The APD array 2 corresponds to the plurality of optical sensors in this invention.

Gamma rays γ incident on the scintillator group 1
2, the scintillator 1 _ij emits light according to the incident position, the emitted light is diffused to the surrounding scintillator 1 _ij , and the light amount is detected by each APD 2 _kl of the APD array 2. If the surface of each scintillator 1 _ij is mirror-finished, the light emission is reflected by this mirror surface, and as a result, the diffusion of the emitted light to the scintillator 1 _ij around the scintillator 1 _ij is suppressed to some extent, and the incident light described later is introduced. The position can be detected more accurately. Also, as shown in FIG.
Reflectors 4 are provided on the respective side surfaces of the scintillator group 1 and on the lower surface on which the gamma rays γ enter, so that the light emission inside the scintillator group 1 is not diffused outside the scintillator group 1.

The detection data (voltage) detected by each APD2 _kl of the APD array 2 and photoelectrically converted is applied to an incident position calculation circuit 3 as incident position calculation means. The incident position calculation circuit 3 obtains the incident position of the gamma ray based on the given detection data of each APD2 _kl , which can be obtained by a scintillation camera system, for example.

Here, an example of a method of calculating the incident position of gamma rays in the case of this embodiment will be described with reference to FIG. For example, for the X direction, each APD2 _kl lined up in the X direction
As shown in FIG. 3A, weights 4m, 3m, 2m, m, -m, -2 corresponding to the position in the X direction are added to the detection data in
m, 3m, -4m (m is a coefficient) is added to calculate the sum (assumed to be A), while each APD2
_The result of adding the detected data in _{kl as} it is (B)
To calculate. Then, the center of gravity of the light amount distribution detected by the APD array 2 in the X direction is obtained by (A / B).

Similarly in the Y direction, the weights 4n, 3n, 2 according to the position in the Y direction are added to the detection data of the APDs 2 _kl arranged in the Y direction, as shown in FIG. 3B.
n, n, -n, -2n, -3n, -4n (n is a coefficient)
The result (B) of adding the detection data of each APD2 _{kl as} it is is calculated while calculating the sum (C) of the results obtained by multiplying
The center of gravity of the light amount distribution detected by the PD array 2 in the Y direction is calculated.

The center of gravity of the light amount distribution in the X and Y directions thus obtained is the position in the X and Y directions corresponding to the light emitting position, and this light emitting position is the incident position of the gamma ray γ.

The optimum m, n, or the weighting method can be experimentally determined in advance depending on the number and arrangement of the scintillators 1 _ij and APD2 _kl .

The incident position calculation circuit 3 is configured, for example, as shown in FIG. 4, so as to perform the above calculation. In addition, DT _{kl in} FIG. 4 is APD
a detection data in _kl (voltage), A _l is, DT _1l to D
The addition value of the result obtained by multiplying T _6l by each weight (-4 _m to 4 m), A _k is DT _{k1 to} DT _k8 and each weight (-4n to 4).
The addition value of the result of multiplying n) is shown.

The method of obtaining the incident position is not limited to the above,
It can be obtained by other methods, and the incident position calculation circuit 3 may be configured according to the incident position calculation method.

[0022] As described above, according to this embodiment, without providing a reflective material between the scintillator 1 _ij, because it binds in close contact with each scintillator 1 _ij, the scintillator 1
_The PF can always be increased regardless of the size of _ij .

Although the APD array 2 is used as the optical sensor in the above embodiment, for example, the position detection type P
MT or multi-segment PMT may be used as the optical sensor.

Further, in the above embodiment, the scintillator 1
_ij and APD2 _kl correspond one to one, but APD2 _kl
Of scintillator 1 _ij may be smaller than the number of scintillator 1 _ij in each of the X and Y directions.
May be many.

Further, in the above _description , the surface of each scintillator 1 _ij is preferably mirror-finished, but may be roughened.

Further, in the above-mentioned embodiment, the scintillator group 1 is constructed by bringing the scintillators 1 _ij into close contact with each other.
A slight gap between the scintillators 1 _ij may be provided to couple each scintillator 1 _ij by interposing an air layer constitute a scintillator array 1. Even in this case, the incident position of the gamma ray γ can be obtained by the same method as described above.
Further, since this gap does not need to have a constant size, the gap may be reduced in proportion to the size of each scintillator 1 _ij . Therefore, the PF can always be increased regardless of the size of each scintillator 1 _ij .

If necessary, a thin reflecting material (a degree to which the emitted light is transmitted, for example, about 0.03 mm) may be interposed in the above-mentioned gap.

[0028]

As is apparent from the above description, according to the present invention, a plurality of scintillators are brought into close contact or close to each other to form a scintillator group, and a plurality of optical sensors are optically provided in the scintillator group. The scintillator has a constant thickness between the scintillators, since the scintillator is provided with the incident position calculation means for detecting the incident position of the gamma ray by obtaining the center of gravity of the light amount distribution based on the detected light amount detected by each optical sensor. Since it is not necessary to provide a reflecting material, the interval between the scintillators can be reduced. Therefore, the scintillator can be downsized without reducing the PF, and the spatial resolution can be improved without lowering the sensitivity of the PET device or the like.

Further, unlike the conventional apparatus, since it is not necessary to provide a reflecting material having a certain thickness between each scintillator, the radiation detector can be easily manufactured and the process of manufacturing the scintillator group can be simplified. It is also possible to reduce the production cost.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a radiation detector according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a diagram for explaining an example of a method for obtaining an incident position of gamma rays.

FIG. 4 is a block diagram showing an example of a configuration of an incident position calculation circuit.

[Explanation of symbols]

1 _ij ... Scintillator 1 ... Scintillator group 2 ... APD array (optical sensor) 3 ... Incident position calculation circuit (incident position calculation means)

Claims (1)

[Claims] 1. A radiation detector that optically couples a plurality of scintillators two-dimensionally coupled to each other and an optical sensor to the scintillator group to detect the incident position of a gamma ray incident on the scintillator group. While forming a scintillator group by bonding each scintillator close to or close to each other, optically couple a plurality of photosensors to the scintillator group, and based on the detected light amount detected by each photosensor, A radiation detector comprising an incident position calculating means for detecting the incident position of a gamma ray by obtaining the center of gravity of the light amount distribution.