Design and simulation study of low-cost 511 keV SPECT/CT imaging of PET tracers in mice

A collimation device for 511 keV small animal SPECT/CT using clinical detectors was investigated as an alternative to dedicated PET/CT. The device consists of a 45 mm thick collimator (lead cylinder with 30 tungsten pinhole inserts) and an animal bed with three-degrees-of-freedom. The device rests on the patient bed of a clinical SPECT/CT scanner, where the gamma cameras rotate around the collimator. The cylinder and pinhole inserts (1.5 mm diameter aperture and 15° cone angle) were designed to provide adequate line-of-sight shielding of 511 keV gamma rays and minimal pinhole penetration. Monte Carlo simulations were performed to evaluate the shielding and imaging performance. Gamma ray leakage was mainly through the pinhole cones rather than the lead cylinder. At the center of the field of view, spatial resolution was estimated to be 2.2 mm, and sensitivity was 0.20% with dual 15.9 mm thick NaI(Tl) detectors. Although the performance is below that of a state-of-the-art small animal PET/CT scanner, this device may be an acceptable low-cost alternative for some laboratories.