Initial performance of the RatCAP, a PET camera for conscious rat brain imaging

The first fully functional prototype of the RatCAP (Rat conscious animal PET) scanner has been constructed and preliminary evaluations have been performed. RatCAP is a miniature, high performance PET scanner designed specifically to image the brain of a rat while directly attached to its head. The goal is to eliminate the need for anesthesia which can confound quantitative brain studies and prevent simultaneous correlations of neurochemistry and behavior. RatCAP is a fully 3D tomograph with a transaxial (axial) field-of-view of 38(18) mm, outside diameter 72 mm, and weight <200 g which is supported by a small tether. A total of 384 LSO crystals are divided among 12 independent detector blocks, each of which contains an avalanche photodiode (APD) photosensor array and a custom-designed ASIC for highly integrated front-end processing. A custom FPGA-based time-stamp module has been designed and implemented, achieving a preliminary system resolution of 13.9 ns FWHM. With a point source in the FOV center, spatial resolution is 2.1 mm FWHM, energy resolution averages 23% FWHM, and sensitivity is 0.7% at an average threshold of 150 keV. Novel offline data processing algorithms have been developed including methods for time and energy calibrations, corrections for physical effects, and a highly accurate iterative image reconstruction. Initial phantom and rat brain images have been obtained