Characterization of detector layers from a 1 mm3 resolution clinical PET system

We are developing a 1 mm³ resolution, high sensitivity PET system for breast cancer imaging. The system comprises two 16.5cm × 10cm × 1.8cm detector panels each containing 2304 position sensitive avalanche photodiodes (PSAPDs) coupled to 8×8 arrays of 1×1×1 mm³ LYSO scintillation crystal elements for a total of 294,912 crystal elements. In each panel, the LYSO-PSAPD detectors are arranged generally parallel to the annihilation photons in layers of 16 detectors wide by 2 detectors deep, with each layer having 2048 crystal elements. The LYSO-PSAPD detectors are multiplexed in pairs in the depth direction ("dual LYSO-PSAPD modules"). The readout system has a modular data acquisition structure based on a 36-channel readout ASIC. Two of these acquisition structures are used to read out a single detector layer. Two sets of eight detector layers are stacked and connected to 32 data acquisition structures and digital back-ends to form two cartridge; nine cartridges are stacked to form each panel. This paper presents the results from an edge-on data of one layer from each panel. A Na-22 point source on a translation stage was used to generate coincident 511 keY photons. List-mode coincidence photon data was collected. The coincidence time resolution data was energy gated to be in the 511 keY photopeak and was corrected for delay from percrystal position and time walk from signal amplitude. Two panels in coincidence are shown to have an energy resolution of 12.13±0.01% FWHM at 511 keY and a paired photon time resolution of 12.2±0.2 ns (8.6±0.2 ns unpaired) FWHM at 511 keY. The horizontal reconstructed width of the 0.25 mm point source was 0.62±0.06 mm FWHM.