High resolution GSO block detectors using PMT-quadrant-sharing design for small animal PET

GSO position-sensitive block detectors have been developed using the PMT-Quadrant Sharing (PQS) design for an animal PET system. Two prototype block detectors with dimensions of 1.51 mm×1.51 mm×10 mm (12×12 array) and 1.66 mm×1.66 mm×10 mm (11×11 array) were built using 19 mm round PMT and ESR mirror-film (98 % reflectance, 0.065 mm thickness, 3M Corporation) windows to control the distribution of scintillation light for the PQS design. The detector pitches are 1.59 and 1.74 mm and the crystal-packing fractions 90, 91 % (area), respectively. List-mode measurements were carried out to test the crystal decoding with Cs-137 sources and analyzed to extract the individual crystal spectra. All the crystals in both crystal-position decoding maps were clearly identified and well isolated. The light collection efficiency is lowest in the central crystals and highest in the crystals of the four corners, with a ratio of 0.76 for the 11×11 array. The overall energy resolution of the 11×11 array is 13.5 % (15.4 % at 511 keV) with a standard deviation of 1.2 %, which indicates that the energy resolution of the detector is very high and uniformly distributed. From this study, we achieved a high crystal/PMT ratio of 144:1. It is believed that these detectors would be useful for a high-resolution animal PET camera.