High spatial resolution PET detectors based on 10 mm × 10 mm linearly-graded SiPMs and 0.5 mm pitch LYSO arrays.

Position-sensitive silicon photomultipliers (PS-SiPMs) are promising photodetectors for ultra-high spatial resolution small-animal positron emission tomography (PET) scanners. This paper evaluated the performance of the latest generation of linearly-graded SiPMs (LG-SiPMs), a type of PS-SiPM, for ultra-high spatial resolution PET applications using LYSO arrays from two vendors. Approach: Two dual-ended readout detectors were developed by coupling LG-SiPMs to both ends of the two LYSO arrays. Each LG-SiPM has an active area of 9.8 mm × 9.8 mm. Both LYSO arrays consist of 20 × 20 arrays of 0.44 mm × 0.44 mm × 20 mm polished LYSOs with a pitch of 0.5 mm. The performance of the two detectors was compared in terms of flood histogram, energy resolution, timing resolution, and depth-of-interaction (DOI) resolutions. Main results: Flood histograms showed clear identification of all LYSO elements except for some edge crystals due to the larger size of the LYSO arrays compared to the active area of the LG-SiPMs and the misalignment between LG-SiPMs and LYSO arrays in the assembled detectors. At a bias voltage of 37.0 V, the detectors utilizing the Tianle LYSO array and EBO LYSO array provided energy resolutions of 17.5 ± 2.2 % and 18.6 ± 2.0 %, timing resolutions of 0.75 ± 0.03 ns and 0.78 ± 0.03 ns, and DOI resolutions of 2.16 ± 0.15 mm and 2.31 ± 0.12 mm, respectively. Significance: The results presented in this paper demonstrate that the new generation LG-SiPMs are promising photodetectors for ultra-high spatial resolution small-animal PET scanner applications.