Quantitative small field-of-view pinhole SPECT imaging: initial evaluation

A quantitative filtered backprojection (FBP) algorithm for small field-of-view pinhole SPECT has been implemented and evaluated. This algorithm compensates for attenuation, scatter, geometric collimator response and system misalignment. Pinhole SPECT quantification with three different pinhole collimators was evaluated using experimentally acquired phantom data. SPECT scans using both in-air and in-water point sources located at different places and a cylinder filled with uniform activity were acquired. Planar scans of an in-air point source from different incident angles were acquired to determine the angular dependence of the geometric collimator response. Images were reconstructed using the FBP algorithm, with geometric response correction, dual-window scatter subtraction (c=0.4), single iteration Chang attenuation compensation, and system misalignment correction. Total activities in point source experiments and concentrations in cylindrical phantom experiments were measured. Accurate quantitative results (<7%) were obtained using the pinhole FBP algorithm