New 9$\,\times\,$9 and 10$\,\times\,$10 BGO Block Detector for Human PET Using PMT Quadrant Sharing Design

Abstract

Our objectives were to develop two 9times9 and 10times10 array high resolution position sensitive block detectors using low cost photomultiplier-quadrant-sharing (PQS) technology. These two blocks can decode 4.3 mm or 3.9 mm BGO crystals with 39 mm size regular round PMT. By using ESR film as reflector between crystals, we achieved 96% packing fractions for these two blocks. Compared with conventional block design using 19 mm or 26 mm PMT, Phi39 mm size PMT can reduce the number of PMT in a camera by 55%-75%. Use of BGO crystal can reduce crystal cost by more than 70% compared to LSO or GSO crystals that are used in some of the newest PET cameras. The BGO crystal sizes-4.3 mm or 3.9 mm-in these two PQS blocks were similar to or smaller than BGO, LSO, or GSO crystals (4-6.3 mm) in commercial human PET cameras. The spatial resolution of the PQS blocks was expected to be similar or better. List mode data of these two blocks were acquired with Na- 22 source. Crystal-decoding map of blocks and individual crystal spectra were derived. All 9times9 and 10times10 crystals were clearly decoded on the block decoding map. These two PQS detectors decoded 81 or 100 BGO crystals per PMT. The average peak to valley ratio of decoding map was 3.4 and 1.8 respectively. The light collection efficiency for all crystals in the blocks were 71%-100% and 66%-100% respectively. The average energy resolutions of all crystals were 16.8% and 17.2% respectively. Our data suggest that even at lower cost the new PQS PET camera may outperform recent conventional PET cameras.