Preliminary evaluation of a compact, high sensitivity and high resolution small animal PET prototype

A compact, high sensitivity and high resolution small animal PET prototype was recently developed at Shenzhen Bay Laboratory (SZBL). This work aims to characterize the detector performance and preliminarily evaluate the system performance of the prototype PET scanner. Following the benchtop design idea, the overall size of the prototype was about twice the size of a commercial desktop PC case. The prototype consists of twenty detector modules arranged in two rings. The diameter is 80 mm and the axial FOV is 104.5 mm. Each detector module is comprised of a two-layer LYSO/BGO pixelated scintillator array, a 1 mm thick lightguide with oblique cuts, and two pieces of 8×8 Hamamatsu S14161-3050HS MPPCs. All MPPC channels were read out by PETsys TOFPET2 ASICs. The front layer (gamma ray entrance) is a 30×60 array of 0.79×0.79×5 mm
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LYSO crystals. The back layer is a 20×40 array of 1.22×1.22×7.5 mm
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BGO crystals. The complete detector module has overall dimensions of 26×52 mm
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.We used charge integration (QDC) and time-over-threshold (ToT) to discriminate the LYSO and BGO layers. All crystal pixels can be resolved thanks to the customized lightguide. The average energy resolution of the detector module was 11.5%± 2.9% for the LYSO layer events and 26.2%± 3.0% for the BGO layer events. With an energy window of 350–650 keV, the coincidence timing resolution (CTR) of the LYSO-LYSO, BGO-BGO and LYSO-BGO coincidences were 598 ps, 2.52 ns and 1.50 ns respectively, and the peak absolute sensitivity was 14.4% including the cross layer crystal scatter (CLCS) events and 11.2 % excluding CLCS events. The average spatial resolution in FWHM using OSEM reconstruction was 0.76 mm.