Department of Radiology, Molecular Imaging Program at Stanford, School of Medicine, Stanford University, CA, United States of America.
Nuclear Emergency & Environmental Protection Division, Korea Atomic Energy Research Institute, Daejeon, Republic of Korea.
Phys Med Biol. 2021 Jun 9;66(12). doi: 10.1088/1361-6560/ac01b5.
Photon time-of-flight (TOF) capability in positron emission tomography (PET) enables reconstructed image signal-to-noise ratio (SNR) improvement. With the coincidence time resolution (CTR) of 100 picosecond (ps), a five-fold SNR improvement can be achieved with a 40 cm diameter imaging subject, relative to a system without TOF capability. This 100 ps CTR can be achieved for adetector design (crystal element length ≥20 mm with reasonably high crystal packing fraction) using a side-readout PET detector configuration that enables 511 keV photon interaction depth-independent light collection efficiency and lower variance in scintillation photon transit time to the silicon photomultiplier (SiPM). In this study, we propose a new concept of TOF-PET detector to achieve high (<2 mm) resolution, using a 'side-coupled phoswich' configuration, where two crystals with different decay times () are coupled in a side-readout configuration to a common row of photosensors. The proposed design was validated and optimized with GATE Monte Carlo simulation studies to determine an efficient detector design. Based on the simulation results, a proof-of-concept side-coupled phoswich detector design was developed comprising two LSO crystals with the size of 1.9 × 1.9 × 10 mmwith decay times of 34.39 and 43.07 ns, respectively. The phoswich crystals were side-coupled to the same three 4 × 4 mmSiPMs and detector performances were evaluated. As a result of the experimental evaluation, the side-coupled phoswich configuration achieved CTR of 107 ± 3 ps, energy resolution of 10.5% ± 1.21% at 511 keV and >95% accuracy in identifying interactions in the two adjacent 1.9 × 1.9 × 10 mmcrystal elements using the time-over-threshold technique. Based on our results, we can achieve excellent spatial and energy resolution in addition to ∼100 ps CTR with this novel detector design.
光子飞行时间（TOF）在正电子发射断层扫描（PET）中的能力可以提高重建图像的信噪比（SNR）。对于直径为 40 厘米的成像对象，若系统具有 TOF 能力，则可以获得相对于没有 TOF 能力的系统提高五倍的 SNR。通过使用侧读出 PET 探测器配置，对于探测器设计，可以实现 100ps 的 CTR（晶体元件长度≥20mm，具有合理高的晶体填充分数），该配置能够实现 511keV 光子相互作用深度无关的光收集效率和闪烁光子传输时间到硅光电倍增管（SiPM）的方差更低。在这项研究中，我们提出了一种新的 TOF-PET 探测器概念，通过使用“侧耦合磷光体”配置，使用两个衰减时间（）不同的晶体，实现了高分辨率（<2mm），该配置在侧读出配置中耦合到公共的一行光电传感器。使用 GATE 蒙特卡罗模拟研究对所提出的设计进行了验证和优化，以确定有效的探测器设计。基于模拟结果，开发了一种概念验证的侧耦合磷光体探测器设计，由两个衰减时间分别为 34.39 和 43.07ns 的尺寸为 1.9×1.9×10mm 的 LSO 晶体组成。磷光体晶体被侧耦合到相同的三个 4×4mm 的 SiPM 上，并评估了探测器性能。实验评估的结果是，侧耦合磷光体配置实现了 107±3ps 的 CTR、511keV 时 10.5%±1.21%的能量分辨率以及使用过阈值技术在两个相邻的 1.9×1.9×10mm 晶体元件中识别相互作用的>95%的准确率。根据我们的结果，我们可以在这个新的探测器设计中实现出色的空间和能量分辨率，以及约 100ps 的 CTR。
