Task-Based Evaluation of Image Reconstruction Methods for Defect Detection and Radiation Dose Reduction in Myocardial Perfusion SPECT

Abstract

We evaluated the ability of conventional and corrective image reconstruction methods to detect a myocardial perfusion defect in single-photon emission computed tomography (SPECT) images using the channelized hotelling observer (CHO). Using our previously developed 4-D extended cardiac-torso, we simulated realistic transmural and endocardial perfusion defects in various locations and sizes in the myocardium. Almost noise-free projection datasets were generated separately from the heart, blood pool, lungs, liver, kidneys, stomach, gall bladder, and the remaining body using Monte Carlo simulation techniques that included the effects of collimator detector response, photon attenuation, and scatter. The datasets were then scaled and combined to model 99mTc Sestamibi myocardial perfusion SPECT projection datasets from a typical patient with various reduced count levels, simulating reduced radiation doses. The final projection data were reconstructed using the 3-D filtered back-projection (FBP) without correction and a 3-D ordered-subset expectation-maximization (OS-EM) method with corrections of attenuation, collimator-detector response, and scatter (ADS), followed by smoothing filtering with several different cut-off frequencies. Task-based evaluations on the reconstructed images were performed by using the CHO followed by the receiver operating characteristics (ROC) methodology to evaluate the detectability of a myocardial perfusion defect by the two image reconstruction methods for various defect anatomies. Areas under the ROC curve (AUC) were computed to assess the changes in the detection of myocardial perfusion defects. The results showed that the 3-D OS-EM with ADS correction gave overall higher AUC values than FBP at several post smoothing levels, count levels, and myocardial perfusion defect sizes. The difference in AUC increased as image smoothness decreased, where the 3-D OS-EM with correction was able to provide similar AUC values with 20%–40% reduction in count levels compared to those of FBP. The AUC values for smaller myocardial perfusion defects were lower for both reconstruction methods with smaller differences. We concluded that the 3-D OS-EM with ADS correction provides higher performance in detecting myocardial perfusion defects. At the conventional count level, it allows for less counts or lower radiation doses without loss of defect detection in myocardial perfusion SPECT images compared to the conventional FBP method, especially regarding less smoothed images.