An improved quadrant-sharing BGO detector for a low cost rodent-research PET (RRPET)

This is a study to improve the detector engineering of a low-cost high-sensitivity rodent-research PET camera (RRPET). The detector system is a solid ring of BGO made of tapered-pentagon blocks, each with 8×8 crystals and an average crystal pitch of 2.0 mm. The detector system used a variation of the photomultiplier-quadrant-sharing design (PQS). The first version of the RRPET blocks used white-paint reflectors of different shapes/sizes to control light distribution to the 4 decoding PMT. In this improved version, the white paint was replaced by a new ESR-mirror film. The film is 0.06 mm thick and mechanically robust. The construction provides a very high crystal-packing fraction (96% linearly) with a gap of only 0.08 mm between crystals. The film construction is more suitable for the slab-sandwich-slice construction we developed to make PQS blocks as the film reduces construction time. Average light output increased by 32% compared to the painted version. The light-output ratio (signal uniformity) between the worst crystal group (in the gap between 4 round PMTs) and the best crystal group (near the middle of a PMT) improved from 53% from 63%. The crystal-decoding resolution has also improved. The detection-efficiency uniformity has improved as well. The energy resolution for individual crystals has improved from 24% to 19% for the corner crystals and from 30% to 22% for the central crystals. The film also has better mechanical precision than paint, thereby positioning the small crystals more accurately relative to each other.