高分辨率高效率三维正电子发射断层扫描成像探测器研发

小动物正电子发射断层扫描成像(Positron Emission Tomography，PET)是临床前生物医学研究的重要工具，但小动物 PET要同时达到高空间分辨率和高效率必须使用三维深度测量探测器。本工作使用位置灵敏雪崩光二极管(Position-Sensitive Avalanche Photodiode，PSAPD)和位置灵敏硅光电倍增管(Position-Sensitive Silicon Photomultipliers，PS-SiPM)双端读出，测量了晶体大小为0.7～0.44 mm的高分辨率硅酸镥晶体阵列，其中对一种最新研发成功的 PS-SiPM进行了首次测试。首先对 PS-SiPM和 PSAPD的信噪比进行了测量，然后对使用 PS-SiPM和 PSAPD的双端读出探测器模块的晶格分辨图、能量分辨率和相互作用深度分辨率分别进行了测量。实验发现，PSAPD的信噪比远远优于 PS-SiPM，使用 PSAPD的探测器可以分辨0.44 mm的晶格阵列和最好达到1.4 mm的深度分辨率，而使用 PS-SiPM的探测器模块可以分辨0.7 mm的硅酸镥晶体阵列和达到2.9 mm的深度分辨率。从得到的晶格分辨图、能量分辨率和相互作用深度分辨率上来看，使用 PSAPD的探测器模块要优于使用 PS-SiPM的探测器。这需要提高 PS-SiPM的信噪比来进一步提高探测器分辨更小截面晶格的能力，提高 PS-SiPM微单元的数量来降低饱和效应从而提高探测器的相互作用深度分辨率。从实验结果可以看出，基于 PSAPD的三维相互作用深度测量 PET探测器具有更好的性能，今后计划使用新的 PS-SiPMs和 SiPM阵列进行该类型探测器的研发。

High Spatial Resolution and High Sensitivity Three Dimensional PETDetector Development with Position-sensitive Avalanche Photodiode andSilicon Photomultiplier Readout

Small animal positron emission tomography (PET) is a well-established imaging modality in preclinical biomedical research. But depth encoding detectors are required to simultaneously achieve high spatial resolution and high sensitivity for a small animal PET scanner. In this work, we evaluated several dual-ended readout detector modules using lutetium oxyorthosilicate (LSO) arrays with crystal sizes ranging from 0.70 mm to 0.44 mm, read out by either position-sensitive avalanche photodiodes (PSAPDs) or position-sensitive silicon photomultipliers (PS-SiPMs). A new type of PS-SiPM was developed recently and was evaluated for the ifrst time in this work. First, the signal-to-noise ratio (SNR) of both PSAPDs and PS-SiPMs was measured, and then the lfood histograms, energy resolution and depth of interaction (DOI) resolution of dual-ended readout detector modules by using both PSAPDs and PS-SiPMs were measured. The PSAPD has much better SNR as compared with PS-SiPM. For the detectors using PSAPDs, crystals as small as 0.44 mm can be resolved and a DOI resolution as good as 1.4 mm was obtained. For the detectors using PS-SiPMs, 0.7 mm crystals can be resolved and a DOI resolution of 2.9 mm was obtained. Based on the results of the lfood histograms, energy resolution and DOI resolution the detector modules using PSAPD are better than those using PS-SiPMs. The SNR of the PS-SiPM would need to be improved to resolve even smaller crystals and the number of SiPM cells also need to be increased to reduce the saturation effect to improve the DOI resolution. The performance of the three dimensional depth encoding PET detectors using PSAPDs is much better because the SNR of PSAPD is much higher than PS-SiPM. In the future, high resolution depth encoding PET detectors will be developed by using both new PS-SiPMs and SiPM arrays.