具有间隙反射膜的稀疏SiPM阵列PET探测器性能评估
Performance evaluation of a PET detector witha sparse SiPM array and gap reflectors

正电子发射断层成像仪（positron emission tomography，PET）通常采用模块化闪烁探测器，由闪烁晶体阵列耦合光电传感器阵列构成。近年来硅光电倍增管（silicon photomultiplier，SiPM）广泛应用于PET。虽然SiPM紧密排列可以获得较好性能，但是稀疏排列可以有效降低成本，获得较高性价比。该文采用SensL公司MicroFB-30035-SMT芯片自主拼接了一款8×8的稀疏SiPM阵列，阵列面积为33.7 mm×33.7 mm，SiPM芯片尺寸为3.16 mm×3.16 mm，即阵列间隙面积比例为44%。基于该稀疏SiPM阵列，开发了一款具有作用深度信息的双层错位LYSO晶体PET探测器模块。SiPM间隙为探测死区，将造成光损失。该文评估了在SiPM间隙粘贴增强型镜面反射膜（enhanced specular reflector，ESR）后对探测器性能的影响。在室温下采集了有无间隙反射膜2种情况下的泛场图像。开发了定量评估方法，评估了探测器的光电峰、能量分辨率和晶体响应均方根误差。结果表明：SiPM间隙粘贴反射膜提高光收集量25.5%，将探测器的能量分辨率由13.48%优化到12.80%；泛场图像质量也有了提升，即改善了探测器固有空间分辨率。
Abstract：Positron emission tomography (PET) usually uses scintillation detectors consisting of crystal arrays and photoelectric sensor arrays. In recent years, silicon photomultipliers (SiPMs) have been more widely used in PET detectors. Although a closely arranged SiPM array can give high performance, a sparse array gives a more cost-effective system. This paper describes a sparse 8×8 SiPM array using the MicroFB-30035-SMT chip from SensL Inc. The array size is 33.7 mm×33.7 mm while the SiPM chip is 3.16 mm×3.16 mm; thus, the gap ratio is 44%. The sparse SiPM array and a dual-layer offset LYSO array were used in a high performance depth PET detector. The gaps between the SiPMs are dead zones which reduce the optical photon collection. Thus, this work studies the effects of adding enhanced spectral reflector films into the gaps. Flood maps were acquired with and without reflectors at room temperature with the crystal response analyzed to find the photopeaks, energy resolution and root-mean square (RMS) of the crystal response. The results show that the reflectors in the gaps effectively enhance the photon collection (25.5% increase) and optimize the energy resolution of the detector (from 13.48% to 12.80%). The quality of the flood map is also improved, i.e. the intrinsic spatial resolution of the PET detector.