Tracking the same fast-LGSO crystals by changing surface treatments for better coincidence timing resolution in PET

Abstract

Achieving fast coincidence timing resolution (CTR) is an important issue in clinical time-of-flight positron emission tomography (TOF-PET) to improve the reconstructed image quality. One of the major factors affecting the CTR is the crystal surface treatment, which is often parameterized as surface roughness. However, previous studies on the crystal surface treatment optimization had two limitations of crystal-by-crystal variation and worse CTR over 200 ps. Here, we report the effects of the crystal surface treatment on the performance of a 20 mm long fast-LGSO crystal based TOF detector by tracking the same crystals in the sub-180 ps CTR regime. The light collection efficiency (LCE), energy resolution (ER) and CTR of the TOF detector were evaluated with six different crystal surface treatments of chemically polished (C.P), C.P half side roughened (1/2S) treatment, and then the C.P one side roughened (1S) treatment, mechanically polished (M.P) treatment, M.P 1/2S treatment, and M.P 1S treatment. The four lateral surfaces of each crystal were wrapped by using enhanced specular reflector film while the top surface was covered by using Teflon tape. The bottom surface of the crystal was optically coupled to a silicon photomultiplier. The timing and energy signals were extracted by using a custom-made high-frequency readout circuit, and then digitized by using a waveform digitizer. All the experimental conditions were same except the crystal surface treatment. Among the six different crystal surface treatments, the M.P 1S would be the optimal crystal surface treatment which balanced enhancements in the CTR (165±3 ps) and ER (10.5±0.5%). Unlike the M.P 1S, the C.P 1S did not enhance the CTR and ER. Hence, the C.P without roughening would be the second-best optimal crystal surface treatment which balanced the CTR (169±3 ps) and ER (10.5±0.5%).

A multi-resolution TOF-DOI detector for human brain dedicated PET scanner

“…The timing resolution was influenced by many factors in the detection chain (Lecoq, 2017). The CTR can be improved further in several ways in terms of the crystal and coupling perspectives by utilizing faster LYSO crystals with co-doping (Nadig et al 2023), optimizing the coupling material and optical reflectors (Pizzichemi et al 2019, Zeng et al 2023, and applying better surface treatments of the crystal and lightguide (Kiyokawa et al 2023). In terms of the electronics and timing algorithms, the CTR could be improved by optimizing the ASIC parameters and overvoltage of MPPCs (Nadig et al 2021), applying a signal amplification before the ASIC input stage (Nadig et al 2022), and using LOR-based finetuning (Zeng et al 2023).…”