Molecular imaging is an important technology to clarify biological and medical uncertainties in the 21th century. This is best realized via in vivo imaging of biological processes in small animals. Thus, a special high resolution imager dedicated for small animals is required. We recently installed a high resolution animal positron emission tomography (PET) scanner (microPET R4) for doing in vivo molecular imaging of gene expression. This paper describes the performance evaluation of our microPET R4 scanner. The microPET R4 scanner is a dedicated PET for studies of rodents. The system is composed of 96 detector modules, each with an 8 × 8 array of 2.1 × 2.1 × 10 mm3 lutetium oxyorthosilicate (LSO) crystals, arranged as 32 crystal rings and 14.8 cm in diameter. The detector crystals are coupled to a Hamamatsu R5900-C8 position sensitive photomultiplier tube (PS-PMT) via a 10 cm long optical fiber bundle. The system operates in 3D mode without inter-plane septa, acquiring data in list mode. A number of scanner parameters such as sensitivity, spatial resolution and energy resolution were determined in this work. In the center of field of view (FOV) a maximal sensitivity of 21.04 cps/kBq was calculated from a measurement with a germanium-68 point source with an energy window of 250-750 keV. Spatial resolution of 2.03 mm (FORB+2D-FBPJ/1.61 mm (FORB + 2D-OSEM) full width at half maximum (FWHM) in the tangential direction and 2.07 mm (2D-FBP)/1.65 mm (2D-OSEM) FWHM in the radial direction were measured in the center with a 0.28 mm diameter 18F-FDG line source. The energy resolution of the scanner was measured across all crystals ranging from 13.9% to around 34.6% with a mean of 18.45%. The results show that the microPET R4 is a suitable PET scanner for imaging small animals like mice and rats.
