Evaluation of a 4D MAP-RBI-EM Image Reconstruction Method for Gated Myocardial SPECT using a Human Observer Study

Abstract

Previously, we investigated a 4D maximum a posteriori rescaled-block iterative (MAP-RBI)-EM image reconstruction method with corrections of image degrading factors for gated myocardial SPECT. It provided a significantly improved trade-off between normalized mean squared error (NMSE) and normalized standard deviation (NSD) of the reconstructed images as compared to conventional reconstruction methods allowing more timing gates per cardiac cycle for better detection of wall motion abnormalities. In this study, we investigate the use of human observer study to evaluate the 4D MAP-RBI-EM method. We used a population of realistic 4D NURBS-based Cardiac-Torso (NCAT) phantoms modeling variations in cardiac motion. Half the population was normal; the other half had hypokinetic cardiac motion abnormalities. Noise-free and noisy projection data with 16 cardiac gates were generated using an analytical projector that included the effects of attenuation, collimator-detector response and scatter (ADS). The projection data were reconstructed using the 3D FBP and 3D OS-EM methods with corrections for ADS followed by a linear filter and the 4D MAP-RBI-EM method with ADS corrections. The reconstructed images were used in a human observer study. The observers were trained to the simulated gated SPECT images animated with a realistic real-time frame rate and were instructed to rate their confidence on the absence or presence of a motion defect on a continuous scale from 1 to 5. We applied receiver operating characteristic (ROC) analysis and used the area under the ROC curve as an index of comparison. The result showed significant differences in detection performance among the different NMSE-NSD combinations. Images obtained from the optimized 4D MAP-RBI-EM with corrections gave better human observer detection performance among the other image reconstruction methods. We conclude that the optimized 4D MAP-RBI-EM method with corrections of image degrading factors provides improvement in detecting wall motion abnormalities in gated myocardial SPECT.