Basic Research on a New Generation PET system (Semiconductor Three Dimensional PET) toward Ultra Low Dose and High Spatial Resolution

首先，针对使用半导体探测器的高分辨率PET系统的发展，研究了几种类型的半导体探测器的性能。制作了三种不同形状的TIBr探测器（12mm^2×0.47mm薄型探测器、9mm^2×3mm块状探测器和16mm^2×0.5mm×10片叠片式探测器），并对其性能进行了评价。用薄探测器获得了0.511keV的峰。由于在低能量侧出现大的噪声，用其它的TIBr探测器没有观察到这个峰。其次，在发展TLBr半导体的同时，研究了CdTe半导体作为PET探测器的时间分辨特性。16mm^2×0.5mm的CdTe半导体PET的时间分辨为15ns。这些结果表明，目前CdTe探测器适合作为小型半导体PET的探测器。我们从理论上研究了PET系统的空间分辨率极限，得到了PET系统的空间分辨率极限为0.8mm，机架直径25cm的情况下。在此基础上，我们制作了一个微型半导体PET，探测器块由0.5×5×5mm^3的CdTe晶体组成，每层两排，间隔2.4mm（共16个探测器）。该装置由两个或两个以上直径<22>分别为1mm和0.6mm的钠热斑组成，其PET图像的空间分辨率为0.5mm，是迄今为止第一台高分辨率PET装置，与现有的PET装置相比，空间分辨率有了很大的提高。

First, the performance of several types of semiconductor detectors was inveatigated aiming at the development of a high resolution PET system using semiconductor detectors. The detectors of TIBr of three different shapes (a thin detector 12mm^2×0.47mm, a block type detector 9mm^2×3mm and a laminated type detector 16mm^2×0.5mm×10 pieces) were made, and their performance was evaluated. The peak of 0.511ke V was obtained with the thin detector. This peak was not observed with the other TIBr detectors, due to a large noise appearing at the low energy side.Second, the time resolution characteristics of CdTe semiconductors as detector foe PET were examined in parallel with the development on TLBr semiconductors. The time resoluhon of the CdTe semiconductor of 16mm^2×0.5mm for PET was 15ns.From these results, it is shown that at present, the CdTe detector is suitable as detector for a small semiconductor PET, and the use of thin detector crystals allows obtaining a good time resolution.We investigated theoretically the limit of spatial resolution for a PET system and obtained a spatial resolution limit of 0.8mm in the case of gantry diameter 25cm. Based on the present results, we built a mini-semicomductor PET, opposing the detector blocks consisting of CdTe crystals of 0.5×5×5mm^3 in four rows of two layers at 2.4mm intervals (16 detectors in total). The hyperfine structure Phantom that consisted of two or more^<22>Na hot spots of 1mm and 0.6mm diameter was tested, and the PET image of these spots was separated with a spatial resolution of 0.5mm.This is the first high resolution PET device to date and demonstrates that considerable improvement in spatial resolution can be obtained compared to existing PET facilities.