National Institute of Radiological Sciences (NIRS), National Institutes for Quantum and Radiological Science and Technology (QST), 4-9-1, Anagawa, Inage-ku, Chiba, Japan.
Department of Senior Healthcare, Graduate School, Eulji University, Daejeon, Republic of Korea.
Biomed Phys Eng Express. 2020 Nov 4;6(6). doi: 10.1088/2057-1976/abc45a.
Silicon photomultipliers (SiPMs) are now widely used for positron emission tomography (PET) applications because of their high gain and low noise characteristics. The PET image quality has been improved with the advancement of time-of-flight (TOF) and depth-of-interaction (DOI) measurement techniques. For brain-dedicated PET systems, both TOF and DOI information are beneficial for enhancing the reconstructed PET image quality. In a previous study, we proposed SiPM-based dual-ended readout PET detectors that used a mean time method to achieve coincidence timing resolution (CTR) of 349 ps and DOI resolution of 2.9 mm. However, the coincidence timing resolution (CTR) was worse than 300 ps since the crystal surface and the reflector type were not optimized. This study aimed at investigating the optimal crystal surface treatment and the reflector material to achieve a sub-200 ps CTR and sub-3 mm DOI resolution with a dual-ended readout PET detector using an LYSO crystal (2.9 × 2.9 × 20 mm). The scintillation light inside the LYSO crystal was read out by two SiPMs using the dual-ended readout method. The CTR and DOI resolution were measured with two different crystal surfaces (polished and saw-cut) and three different reflector material scenarios of ESR without grease (i.e., air coupling), ESR with optical grease and Teflon. We digitized the timing and energy signals by using a V775N TDC module (35 ps bit) and V965 QDC module, respectively. The combination of the saw-cut LYSO crystal and the ESR with air coupling resulted in the best CTR (188 ± 32 ps) and DOI resolution (2.9 ± 0.2 mm) with the dual-ended readout configuration. We concluded the dual-ended readout method in combination with the saw-cut crystal and the ESR reflector with air coupling can provide a sub-200 ps CTR and sub-3.0 mm DOI resolution simultaneously.
硅光电倍增管（SiPM）由于其高增益和低噪声的特点，现在被广泛应用于正电子发射断层扫描（PET）应用。随着飞行时间（TOF）和交互作用深度（DOI）测量技术的进步，PET 图像质量得到了提高。对于专门用于脑部的 PET 系统，TOF 和 DOI 信息都有利于提高重建 PET 图像的质量。在之前的研究中，我们提出了基于 SiPM 的双端读出 PET 探测器，该探测器使用平均时间方法实现了 349 ps 的符合时间分辨率（CTR）和 2.9mm 的 DOI 分辨率。然而，由于晶体表面和反射器类型没有优化，因此符合时间分辨率（CTR）差于 300 ps。本研究旨在研究最佳的晶体表面处理和反射器材料，以使用双端读出 PET 探测器实现具有 LYSO 晶体（2.9×2.9×20mm）的亚 200 ps 的 CTR 和亚 3mm 的 DOI 分辨率。LYSO 晶体内部的闪烁光通过双端读出方法由两个 SiPM 读取。通过两种不同的晶体表面（抛光和锯切）和三种不同的反射器材料方案（无油脂的 ESR，即空气耦合）、带光学油脂的 ESR 和 Teflon 测量了 CTR 和 DOI 分辨率。我们分别使用 V775N TDC 模块（35 ps 位）和 V965 QDC 模块对定时和能量信号进行数字化。锯切 LYSO 晶体与带空气耦合的 ESR 的结合实现了双端读出配置下最佳的 CTR（188±32 ps）和 DOI 分辨率（2.9±0.2mm）。我们得出结论，双端读出方法与锯切晶体和带空气耦合的 ESR 反射器相结合，可以同时提供亚 200 ps 的 CTR 和亚 3.0mm 的 DOI 分辨率。
