Design of an inexpensive high-sensitivity rodent-research PET camera (RRPET)

Abstract

A small animal PET is being developed. The design goals are lower cost, higher sensitivity and same image resolution as commercial animal PET. It uses a new version of our PMT-quadrant-sharing (PQS) detector with a 98% crystal-packing fraction to maximize sensitivity and no light-guides to maximize light output (decoding resolution). It uses 168 low-cost 19-mm PMT and 9216 BGO for its high photoelectric fraction. Each block is 8x8 with an average pitch of 2x2 mm (10mm deep) to provide image resolution similar to commercial systems using LSO, position-sensitive PMT and optical fibers. The number-of-crystals-per-PMT decoding ratio achieved was 55, similar to an animal PET using GSO that has 3 times more light output than BGO. To maximize image resolution, we "circularize" the PQS detector design, where each block is one side of a 24-sided polygon (the detector ring). Circularizing PQS detector requires the block to be ground slightly into a pentagon (166° apex). The edge rows of crystals in the block are also tapered, so that blocks can be glued together to form a solid BGO ring with nearly 100% packing. The ring diameter is 13 cm. 6 rings provide a 12-cm axial FOV. The large axial FOV increases coincidence sensitivity.An automatic PMTequalization system can tune the PET in 1 minute without radiation, for PMT tuning before each study to minimize the effects of prior radiation loading and temperature drift. Detector-pileup-recovery electronics were used to prevent imaging artifacts and count-loss in BGO detectors. Experiments showed that 2x2x10 mm BGO can be decoded (energy resolution 23%). Monte Carlo simulation showed a detection efficiency of 5.9% (350-700 KeV) for a central point source. The 3.7x increase in coincidence sensitivity comes from (a) larger axial-FOV (1.8x), (b) BGO higher photoelectric fraction (1.5x) and (c) high packing fraction (1.3x).

Effects of system geometry and other physical factors on photon sensitivity of high-resolution positron emission tomography

“…Small animal PET systems may be used to non-invasively study the molecular bases of certain diseases and efficacy of new treatment regimes in small animal models. Commercial small animal PET systems , 2001, Laforest et al 2004, Wong et al 2003, Yang et al 2004, Zhang et al 2005b, Ziemons et al 2005, Missimer et al 2004, Domenico et al 2002, Bloomfield et al 1997 have been developed that yield 1-2.5 mm spatial resolution at the system center. The coincidence photon detection efficiency ('photon sensitivity') achieved for these systems ranges between 1 and 10% for a point source at the center of the field of view (FOV).…”