Performance evaluation of S-PET, a compact, high sensitivity and high resolution small animal PET prototype

S-PET is a compact, high sensitivity and high resolution small animal PET prototype developed at Shenzhen Bay Laboratory. The prototype system is currently being evaluated at Cancer Hospital Chinese Academy of Medical Sciences, Shenzhen Center. The prototype consists of twenty detector modules arranged in two rings. The system diameter is 80 mm and the axial field of view (FOV) is 104.5 mm. Each detector module is comprised of a two-layer LYSO/BGO pixelated scintillator array and two pieces of 8×8 Hamamatsu S14161-3050HS MPPCs. All MPPC channels were readout by PETsys TOFPET2 ASICs. The inner layer is a 30×60 array of 0.79×0.79×5 mm³ LYSO crystals. The outer layer is a 20×40 array of 1.22×1.22×7.5 mm³ BGO crystals. The peak absolute sensitivity was 14.4% including cross-layer crystal scatter (CLCS) events and 11.2% excluding CLCS events at the center of the FOV. The average detector energy resolution derived by averaging the individual crystal spectra was 11.5 ± 2.9% for LYSO and 26.2 ± 3.0% for BGO. The coincidence timing resolution was 0.76 ± 0.08 ns, 2.06 ± 0.25 ns, and 3.17 ± 0.46 ns for LYSO-LYSO, LYSO-BGO and BGO-BGO coincidences, respectively. The image spatial resolution of a point source reconstructed by maximum likelihood expectation maximization with a spatially variant point spread function modeling has an average value of 0.70 ± 0.09 mm. The peak noise equivalent count rate and scatter fraction were 124 kcps at 6.3 MBq and 7.2% for the mouse-sized phantom, and 80 kcps at 7.2 MBq and 12.6% for the rat-sized phantom. For the NEMA image quality phantom (120μCi), the uniformity was 8.2%, and the spillover ratios measured in the water- and air-filled cold region chambers were 24.9% and 3.6%, respectively.