高分辨率小动物PET探测器边缘晶体分辨能力的提升方法研究

小动物PET成像系统是临床前生物医学研究的重要工具，但通常高分辨率PET探测器模块不能对边缘晶体单元做出清楚无误的鉴别，造成晶体阵列端面小于SiPM阵列面积，使得PET成像系统中探测器模块间隙增加，效率下降。本项目在我们前期研发的高分辨率双端读出深度测量PET探测器的基础上，研究提高探测器对边缘晶体的分辨能力的方法。拟采用两种新的探测器设计方案，第一种是在SiPM阵列边缘使用比中心小的SiPM单元；第二种是在晶体阵列边缘使用和中心发光衰减时间不同的晶体材料，通过脉冲形状分析，对两种晶体做出鉴别。计划通过闪烁光子产生和传输过程的蒙特卡罗模拟技术，对晶体探测器的参数进行优化。目标是研发晶体阵列端面和SiPM阵列面积一样，所有晶体单元可以清楚无误分辨，晶体大小达到0.5mm的超高位置分辨率、高深度分辨率和高效率PET探测器，为今后研发分辨率接近物理极限的高灵敏度小动物PET成像仪器奠定基础。

The small animal Positron Emission Tomography (PET) scanner is an important tool for preclinical biomedical research. However usually the edge crystals of a scintillator array cannot be clearly resolved in high resolution PET detector modules, which results in that the size of the scintillator array is usually smaller than that of the silicon photomultiplier (SiPM) array. This creates a large space between detectors modules in a PET scanner and significantly reduces the sensitivity of the PET scanner. Based on the excellent results of our previous work on developing high resolution PET detectors by using dual-ended readout, in this proposal, two novel PET detector designs are proposed to improve the identification of the edge crystals of the detectors. In the first design, the pixel size of SiPMs used at the edge of a SiPM array is smaller than that of the center SiPMs. In the second design, the decay time of the crystals at the edge of the scintillator array is different from that of the center crystals. The two types of scintillator crystals can be identified by using pulse shape analysis. A Monte Carlo simulation will be carried out to study the process of scintillation photon production and transportation in the detector to optimize the parameters of the detectors. The final goal of this proposal is to develop a PET detector with the size of the scintillator array the same of the size of the SiPM array, with all crystals clearly resolved and crystal size down to 0.5 mm to achieve ultra-high position resolution, high depth of interaction resolution and high sensitivity. The outcome of this work will set a solid foundation to develop a small animal PET scanner with spatial resolution approaching the physical limit and high sensitivity in the future.