Performance evaluation of a new gamma imager for small animal SPECT applications

In this work we characterized a recently developed gamma imager for small animal SPECT applications. The Hamamatsu C9177 is a mini-gamma camera that integrates the detector and all the electronics, including the acquisition system, in a compact and portable housing. The detector is based on a high resolution parallel hole collimator, a CsI(NaI) crystal array and a PS-PMT (flat panel type). The active field of view is 41.9 times 41.9 mm² and the assembly is optimized for 60 to 200 keV. The electronics in the housing includes the high voltage divider, an ASIC which converts the 64 anodes into Anger-like signals, ADCs which are fed with these signals and position and energy lookup tables which allow digital information for each detected photon to be obtained directly from the imager. In order to be able to obtain tomographic data and to improve the measurement protocols, we mounted the detector in a custom-built motorized gantry. We evaluated detector uniformity and energy resolution using a flood field image. Planar intrinsic spatial resolution and spatial linearity were assessed by stepping a capillary source across the detector surface and plotting the count profile for each individual crystal of the array. We additionally performed phantom studies to preliminarily characterize the tomographic performance. Energy resolution is 11.6% (mean), sensitivity is 2.54 cps/muCi and planar spatial resolution is 2.4 mm (CFOV 20 % energy window) when the source is placed on the detector surface.