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) technology for animal PET imaging. Two prototype block detectors with dimensions of 1.51 mm x 1.51 mm x 10 mm (12 x 12 array) and 1.66 mm x 1.66 mm x 10 mm (11 x 11 array) were built using 19 mm round PMTs. The Enhanced Specular Reflector mirror-film (98% reflectance, 0.065 mm thickness, 3M Co.) was used to control the light collection and distribution in the PQS design. The detector pitches are 1.59 (12 x 12) and 1.74 mm (11 x 11) and the crystal-packing fractions 95.0 and 95.4%, respectively. List-mode measurements with Cs-137 sources were carried out to investigate the crystal decoding and analyzed to extract the individual crystal spectra. All the crystals in both the detectors 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 x 11 array. The overall energy resolution of the 11 x 11 array is 13.5% (15.4% at 511 keV) with a standard deviation of 1.2%, which indicates that the individual energy resolutions of the detector are high and uniformly distributed. From this study, we achieved a high decodable crystals/PMT ratio of 144:1 for the 19 mm PQS GSO detector technology with crystals 10 rum deep. It is believed that these detectors would be useful for high resolution animal PET imaging.