Quantitative SPECT reconstruction using multiray projection integrators

In pursuit of the goal of absolute quantitation with SPECT, the authors have previously developed a method for deriving optimal multiray projection integrators. These integrators are derived based on models of the depth-dependent blurring associated with collimated detectors. Here, the authors demonstrate the use of these integrators in iterative SPECT reconstruction codes. Data for these studies was acquired on the emission-transmission CT (ETCT) system developed in the authors´ laboratory. The authors modeled the efficiency of the HPGe array used on the ETCT system using Monte Carlo methods, and they derived quantitative multiray integrators for the ETCT collimator. The projection integrators also accounted for attenuation, however, scatter was ignored. Using these methods, and without the use of a calibrated reference, the authors found they can reconstruct images of a uniformity phantom with activities within 10% of the known activity. In addition, the authors observe improved contrast and resolution in SPECT cardiac images of pigs using these methods, as well as better accuracy. However, the authors could not discern differences in the precision of the uptake methods in these studies