Comparison of 180° and 360° iterative reconstruction with non-uniform attenuation compensation for SPECT

This simulation study compares Tl-201, cardiac SPECT images reconstructed from 180° and 360° emission projection data, using iterative reconstruction with non-uniform attenuation compensation. The images reconstructed with attenuation compensation are compared to each other and to images reconstructed without attenuation compensation. Using a mathematical phantom of the human thorax, Monte Carlo simulation is used to produce both 180° (45° RAO to 45° LPO) and 360° SPECT projection data for a 74 keV radionuclide (T1-201). Included in the simulation are the effects of non-uniform attenuation, detector response, and scatter. The 180° and 360° data were taken over 64 and 128 angles respectively, assuming the same total acquisition time for both. The simulated projection data were reconstructed with nonuniform attenuation compensation using the ML-EM algorithm for 50 iterations and, for comparison, were also reconstructed without attenuation compensation using the filtered backprojection method with a ramp filter. Transaxial slices of the reconstructed images, image profiles and Bull´s-eye plots all show that images reconstructed with attenuation compensation, unlike those reconstructed without attenuation compensation, are essentially the same in the myocardial region for the 180° and 360° data, with few artifacts and similar image contrast. Furthermore, for the same total imaging time, the images reconstructed from the 180° data have slightly less noise in the myocardial region