Abstract：
Objective. Time-of-flight (TOF) is an important factor that directly affects the image quality of PET systems, and various attempts have been made to improve the coincidence resolving time (CRT) of PET detectors. For independent readout detectors, the timing is acquired for each silicon photomultiplier (SiPM), so they are less sensitive to diffused scintillation light, resulting in a better CRT. Further improvement can be expected if the light can be focused on a single SiPM. However, existing SiPM arrays have a thin protective cover on the SiPM and the gap between the SiPMs is filled with either air or the protective cover, so the light must diffuse through the cover. In this work, we investigated optical crosstalk in the protective cover to improve the CRT.Approach. We used 3.1 × 3.1 × 20 mm3fast LGSO crystals and 3 mm square 8 × 8 multi pixel photon counter (MPPC) arrays. Pitch of the MPPCs was 3.2 mm and thickness of the protective cover on them was 150μm. To reduce diffusion of scintillation light in the protective cover, the part of the inactive areas on the MPPC array were optically separated using reflective material. Specifically, 50, 100, 150, and 350μm deep grid-shaped slits were made along the inactive area of the MPPCs and they were filled with BaSO4powder as the reflective material.Main results. Coincidence counts were measured with a pair of TOF detectors, and the CRT was shorter with a deeper slit depth. The CRT before improvement was 235 ps, and using the cover having the 350μm deep slits filled with reflective material lowered the CRT to 211 ps.Significance. Up to 10% of the scintillation light was diffused to other MPPCs by the protective cover, and the CRT was degraded by 10% due to optical crosstalk of the cover. The proposed method promises to improve the CRT of the TOF detector.
摘要：
目的：＆＃xD;飞行时间（TOF）是直接影响PET系统图像质量的重要因素，并且已经进行了各种尝试来改善PET探测器的符合分辨时间(CRT)。对于独立的读出检测器，获取每个硅光电倍增器(SiPM)的时序，所以它们对漫射的闪烁光不那么敏感，导致更好的CRT。如果光可以聚焦在单个SiPM上,则可以预期进一步的改进。然而,现有的SiPM阵列在SiPM上具有薄的保护盖，并且SiPM之间的间隙填充有空气或保护盖，所以光线必须通过盖子扩散。在这项工作中,我们研究了保护套中的光学串扰，以改善CRT。
方法。＆＃xD;我们使用了3.1×3.1×20mm3fastLGSO晶体和3mm正方形8×8多像素光子计数器（MPPC）阵列。MPPC的间距为3.2mm,保护盖的厚度为150μm。为了减少保护罩中闪烁光的扩散，MPPC阵列上的非有源区域的部分使用反射材料光学分离。具体来说,沿MPPC的非活性区域制作50、100、150和350μm深的网格状狭缝，并填充BaSO4粉末作为反射材料。
主要结果。
重合计数是用一对TOF探测器测量的,CRT较短，狭缝深度更深。改进前的CRT是235ps，并且使用具有填充有反射材料的350μm深的狭缝的盖子将CRT降低到211ps。
Significance。＆＃xD;多达10％的闪烁光被防护罩漫射到其他MPPC，并且由于盖的光学串扰,CRT降低了10%。所提出的方法有望改善TOF检测器的CRT。
