Performance evaluation of the low-cost high-sensitivity rodent research PET (RRPET) camera using Monte Carlo simulations

BGO pentagonal blocks are used to build a solid detector cylinder for a rodent research PET (RRPET). With the PMT-quadrant-sharing design, this camera is low-cost and has higher sensitivity than commercial animal PET. The performance parameters of RRPET are obtained using Monte Carlo simulations by GATE, a newly developed toolkit based on GEANT4 for PET/SPECT. Two models of the RRPET system, one 30-sided-polygon geometry model and one 10-sided-polygon electronics model with different time-response constants, are used in the simulations to get the accurate results for both geometry-related and time-related parameters, including the sensitivity, count rate and resolution. Several types of sources are simulated, including a point source, a linear source, and several uniform sources simulating the mouse and the rat. The simulations give the noise equivalent count rate (NECR) curves with the maximum NECR of 2.2 Mcps @ 1.5 mCi for point source, 750 kcps @ 1.5 mCi for mouse-like source and 290 kcps @ 1.0 mCi for rat-like source; the sensitivity is 10.3%; the spatial resolution at the center of the field of view (FOV) is 1.6 mm for an ¹⁸F source inside water phantom; the radial and tangential resolution at the edge of the FOV (10 cm) is 3.2 mm and 2.2 mm, respectively. Preliminary experiments showed a sensitivity of 8.4% to 10.2% (depending on electronics) and a resolution of 1.8 mm with a ²²Na source. By comparing the simulation and experiment results, the resolution degradation from the mechanical misalignment and the block-decoding blurring is found to be 1.1 mm