JPH0627856B2 - Radiation position detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a nuclear medicine diagnostic apparatus for injecting a radioisotope (RI) into a body of a subject to obtain a distribution image thereof, and particularly to a radiation position detector thereof. .

2. Description of the Related Art A conventional scintillation camera uses a mechanical collimator, but has a fundamental problem that detection efficiency and spatial resolution are not compatible.

Recently, an electric collimator as a means for efficiently imaging a single photon emitter has been proposed by M. Singh et al. (Med.Phy.Vol10, No.4,1983,421-42).
7). As shown in FIG. 3, the Ge detector 3 is placed in front of the scintillation camera, the Ge detector 3 and the scintillation camera 4 perform simultaneous counting, and energy information and position information from the Ge detector 3 and the scintillation camera 4 are detected. Based on the position information from the source, the source finds the cone on its surface. That is, the γ-rays emitted from the radiation source are incident on the Ge detector 3 and are Compton-scattered, and the scattered rays are emitted in different directions by a certain angle, and then enter the scintillation camera 4 to cause a photoelectric effect.
The angle of this scattered ray can be known from the energy information obtained by the Ge detector 3. Therefore, the source exists in a direction different from the straight line connecting the position detected by the Ge detector 3 and the position detected by the scintillation camera 4 by the above angle, that is, the source exists on the surface of a certain cone. I understand. By collecting a lot of information about such a cone and backprojecting it, the distribution image of the radiation source can be reproduced. In this case, there is an advantage that the detection efficiency is extremely high because no mechanical collimator is used.

However, in this case, since the scintillation camera 4 is only placed behind the Ge detector 3, only the forward scattered rays of γ rays can be detected by the scintillation camera 4.
Therefore, about ^99m Tc γ-rays (141 KeV), there is a problem that less than half of scattered rays are not counted. Klei
The differential scattering cross section calculated by the n-Nishina formula is 4th
As shown in Fig. 4, from ^99m Tc γ-rays (141 KeV), the infinitesimal angular scattering cross section is 80mb / sr, electron, and the 180 ° reverse scattering cross section is 50mb / It is sr, electron, and it can be seen that when 141 KeV γ-rays cause Compton scattering, half of the strong light is scattered forward and the other half is weakly scattered back. Such a little less than half of the backscatter is conventionally not counted.

Therefore, another scintillation camera may be placed in front of the Ge detector 3 to detect backscattering to further improve the detection efficiency. However, the scintillation camera is placed in front of the Ge detector 3. Since the incident γ-rays do not reach the Ge detector 3, such a configuration is impossible.

In addition, the spatial resolution and maximum count rate of this entire system are
There is a problem that the detection efficiency is dramatically improved as described above because it is limited by the intrinsic spatial resolution and the maximum counting rate of the scintillation camera 4.

An object of the present invention is to provide a radiation position detector capable of further improving the detection efficiency by detecting not only the forward scattered rays but also the back scattered rays and sufficiently utilizing the excellent detection efficiency. .

Means for Solving Problems A radiation position detector according to the present invention comprises a Ge detector,
And a MWPC detector arranged so as to surround the Ge detector, wherein the Ge detector and the MWPC (multiwire proportional counter) detector perform simultaneous counting, and energy information and position information from the Ge detector are provided. And the position information from the MWPC detector determine the cone on which the source lies on its surface.

Action Since the MWPC detector can transmit γ-rays and the scattered rays can generate a photoelectric effect, it is possible to arrange the MWPC detector in front of the Ge detector so as to surround the Ge detector.
Therefore, it becomes possible to detect scattered rays scattered in various directions without leakage, and the detection efficiency is further improved.

Moreover, since the MWPC detector is superior to the scintillation camera in both the intrinsic spatial resolution and the maximum count rate, even if the detection efficiency is improved as described above, it can substantially support it and the principle superiority can be realized. .

Embodiment In FIG. 1, the MWPC detector 1 is arranged behind the Ge detector 3 and the MWPC detector 2 is arranged in front thereof. These MWPC detectors 1 and 2 are Xe gas sealed at high pressure, have a large number of cathode wires and anode wires arranged in a two-dimensional direction in a plane, and incident γ-rays cause a photoelectric effect. And the position information of the event in the two-dimensional direction is obtained. The reason why the MWPC detector 2 placed in front is thinner is that this MWPC detector 2 transmits incident γ-rays and causes only the backscattered rays to generate a photoelectric effect.

That is, the energy of the backscattered ray is considerably lower than that of the incident γ-ray or the forward scattered ray (for example, when the energy of the incident γ-ray is 141 KeV, the energy of the backscattered ray in the 180 ° direction is 90 KeV, 90 °. The energy of scattered rays in the direction is about 110 KeV), so this MWP
By adjusting the pressure of the C detector 2 and the thickness of the sensitive region, most 140 KeV photons are allowed to pass, and 90 to 11
It is said that 0 KeV photon causes a photoelectric effect. If the probability of causing the photoelectric effect of the Xe-encapsulated MWPC detector is plotted as a function of the energy Eγ of incident γ rays,
It becomes like the figure. The probability of Compton scattering is very small in this energy range compared to the photoelectric effect, so it can be ignored. From this FIG. 2, the MWPC detector 2 is set to P.t.
= 50 atm · cm, 80% of 141 KeV photons can be transmitted, and the photoelectric effect can be generated for 50% of 90 KeV photons. Regarding the MWPC detector 1 placed behind the Ge detector 3, it is necessary to detect 141 KeV photons as much as possible, so the value of P · t is increased.

By thus disposing the MWPC detector 2 in front of the Ge detector 3 as well, the detection efficiency is improved. And Ge
By providing the MWPC detector 1 behind the detector 3 instead of disposing the scintillation camera as in the conventional case (FIG. 3), the spatial resolution of the entire system of this radiation position detector can be improved. The overall spatial resolution is determined by the energy resolution of the Ge detector 3, the width and thickness of each element, and the inherent resolution of the MWPC detectors 1 and 2, and the MWPC detector 1 has a characteristic resolution higher than that of the scintillation camera. This is because the overall spatial resolution is improved due to the excellent. Further, since the mechanical collimator is not used, the MWPC detector 1 is put under a very high counting rate. If this is a scintillation camera as shown in FIG. However, it is necessary to take measures such as providing multiple counting circuits.
Since it is a C detector, the maximum count rate is excellent, and thus such a need is not necessary.

In the end, by using the MWPC detector also behind the Ge detector 3, the radiation efficiency is very high as a whole, the radiation efficiency is very high and the spatial resolution and count rate characteristics are excellent. The position detector can actually be realized.

Although the MWPC detectors are placed only behind and in front of the Ge detector 3 in the above embodiment, the detection efficiency can be further increased by placing the MWPC detectors above, below, or in the lateral direction.

Effects of the Invention According to the present invention, it is possible to realize a radiation position detector having improved detection efficiency, spatial resolution, and count rate characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is an incident γ
FIG. 3 is a graph showing a probability of causing a photoelectric effect with respect to the energy of a line, FIG. 3 is a schematic view of a conventional example, and FIG. 4 is a graph showing a differential scattering cross section. 1, 2 ... MWPC detector 3 ... Ge detector 4 ... Scintillation camera

Claims (1)

[Claims] 1. A Ge detector and an MWPC detector arranged so as to surround the Ge detector, wherein the Ge detector and the M detector are provided.
Radiation position detection, in which coincidence counting is performed with the WPC detector, and the radiation source finds a cone on its surface based on the energy information and position information from the Ge detector and the position information from the MWPC detector. vessel.