Development and preliminary performance evaluation of a small animal dedicated SPECT system

SPECT system using NaI(Tl) scintillation crystal and position-sensitive PMT (Hamamatsu, R3292MOD) was developed for small animal imaging. In this study, preliminary physical performance of this system was evaluated. Pinhole collimator with a small aperture (diameter = 1.0, 0.5, and 0.25 mm) was used for the measurement of system performance. For the measurement of system sensitivity, a Tc-99m point source (inner diameter: 1.2mm) was positioned along the central axis of the pinhole collimator at a various distances from the pinhole aperture. Spatial resolution was measured using a Tc-99m line source (inner diameter: 0.4mm), which was positioned at 1 cm from the pinhole aperture. Intrinsic uniformity was measured using a point source without collimator, and linearity was measured using Tc-99m flood phantom and lead sheets on which the 1-mm or 4.8-mm holes were drilled homogeneously. Sensitivity, which was decreased as the square of distance between object and aperture, was 52.4 (1.0 mm aperture), 28.0 (0.5 mm), and 19.6 cps/MBq (0.25 mm) at 1 cm from the aperture. Resolution without correction for the source dimension was 0.97 and 0.66 mm for the 1.0 and 0.25 mm diameter pinhole, respectively. Linearity in horizontal direction was slightly better than in vertical direction. Preliminary performance of small animal SPECT system was evaluated and we expect this system will be useful for small animal imaging after proper corrections for various physical artifacts