Investigation of position sensitive avalanche photodiodes for a new high-resolution PET detector design

We are developing a high-resolution PET detector design with a goal of nearly complete scintillation light collection in less than or equal to 1 mm width, greater than or equal to 20 mm effective thickness LSO crystals. The design uses position sensitive avalanche photodiodes in novel layered configurations that significantly improve the light collection aspect ratio. To reduce design complexity and dead area we are investigating the use of 1 mm thick sheets of LSO in addition to discrete crystal rods, and the use of PSAPDs which require only four readout channels per device. The raw spatial response of a 1 mm thick crystal sheet coupled to a PSAPD exhibits a compressed dynamic range compared to that observed with discrete crystals. Measurements with the proposed configurations using Na-22. irradiation achieved 10%-13% FWHM energy resolution at 511 keV and 2 ns coincidence time resolution. 1 mm width crystals with a saw cut surface finish an no inter-crystal reflector were well resolved in flood images.