Performance characteristics of four new high resolution L(Y)so detectorblocks for human PET

Using standard circular photomultipliers in quadrant sharing configuration (PQS), four new high resolution L(Y)SO detector blocks for human PET applications have been developed. The detector blocks were assembled in very large arrays of 14times14, 15times15, and, 16times16 for two of them. The crystal pitch sizes were 2.74times2.74times20 mm³, 3.25times3.25times20 mm³, 2.42times2.42times20 mm³, 2.78times2.78times20 mm³ and the surface finishing was 4-mum. Mirror films patterns were placed between crystals as reflectors. The blocks were assembled using optical grease and wrapped by Teflon tape. To acquire list mode data of Ga-68 source (511 KeV) with at high voltage bias of 1100 V, these blocks were coupled to regular round PMT´s of 39/51 mm and, crystal decoding maps, individual crystal energy resolutions and relative light-collection efficiencies were extracted from this data. To investigate the potential imaging resolution of the human PET scanners with these blocks, GATE (Geant4 application for tomographic emission) simulation package was used. The packing fractions of these blocks were found to be 97%, 97% and 95%-97%. From decoding maps, all 196, 225 and 256 crystals were clearly identified. The average energy resolutions were 14.3%, 15.5% and 13.1%/14.2%. The relative collection efficiencies were 0.81~1.00, 0.83~1.00 and, 0.77~1.00/0.78~1.00. From this study we can conclude that the PQS design has the potentiality to achieve high spatial resolution and excellent energy resolutions on human PET scanners with substantially lower production cost.