Development and preliminary results of Xtrim-PET, a modular cost-effective preclinical scanner

We report on development of Xtrim-PET, a prototype low-cost preclinical PET system using high-density analog silicone photomultiplier (SiPM) arrays and pixelated scintillator LYSO:Ce crystals. Channel reduction method is employed to reduce 144 SiPM signals per detector block to 16 energy and 9 fast signals in the detector head. Using these signals, a Digital Front-End (DFE) board calculates energy, position, and time information of incident gamma photon and transmits data packets to a downstream Digital Coincidence Processing Unit (DCPU) in which the coincidence events are extracted in a fully pipelined digital processing fashion for maximum count throughput. The system consists of 10 detector blocks (detector head and DFE board), a DCPU board, and an acquisition computer. Prompt and delayed coincidence events are stored in list mode in the acquisition computer where first hand corrections are applied and 3D sinogram is generated in offline mode. Two-dimensional sinograms are then generated using single-slice rebinning algorithm and iterative image reconstruction methods are employed to generate the 3D image. The developed scanner works in room temperature without additional cooling system and has 180 mm ring diameter. Tomographic image resolution of 1.6, 1.7, and 1.8 mm FWHM was calculated along radial, tangential, and axial directions, respectively. Preliminary investigations were performed using NEMA image quality phantom in addition to rat cardiac and bone scans for preclinical evaluation of the scanner.