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

本文首先研究了几种半导体探测器的性能，旨在开发一种基于半导体探测器的高分辨率正电子发射计算机断层扫描系统。制作了3种不同形状的TIBr探测器(12 mm×0.47 mm薄型探测器、9 mm×2 mm×3 mm块型探测器和16 mm×0.5 mm×10片叠层型探测器)，并对其性能进行了评价。用薄探测器获得了0.511keV的峰值。其次，结合TLBr半导体的发展，研究了作为PET探测器的CdTe半导体的时间分辨特性。16 mm×0.5 mm的CdTe半导体对PET的时间分辨率为15 ns。结果表明，目前该探测器适合作为小型半导体PET的探测器，并且使用较薄的探测器晶体可以获得良好的时间分辨率。我们从理论上研究了PET系统的空间分辨率极限，得到了在机架直径为25 cm的情况下的空间分辨率极限为0.8 mm。在此基础上，我们制作了一台小型半导体型正电子发射体层析探测器，探测器块由0.5×5×5 mm×3的CdTe晶体组成，每排两层，间隔2.4 mm(共16个探测器)。测试了由两个或多个直径分别为1 mm和0.6 mm的热点组成的超精细结构体模，并以0.5 mm的空间分辨率分离了这些热点的PET图像。这是迄今为止第一个高分辨率的PET设备，表明与现有的PET设备相比，在空间分辨率方面可以获得相当大的提高。

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.