Comparison of ordered subsets expectation maximization and Chang's attenuation correction method in quantitative...

Photon attenuation is one of the primary causes of artifacts in cardiac single photon emission tomography (SPET). Several attenuation correction algorithms have been proposed. The aim of this study was to compare the effect of using the ordered subsets expectation maximization (OSEM) reconstruction algorithm and Chang's non-uniform attenuation correction method on quantitative cardiac SPET. We performed SPET scans of an anthropomorphic phantom simulating normal and abnormal myocardial studies. Attenuation maps of the phantom were obtained from computed tomographic images. The SPET projection data were corrected for attenuation using OSEM reconstruction, as well as Chang's method. For each defect scan and attenuation correction method, we calculated three quantitative parameters: average radial maximum (ARM) ratio of the defect-to-normal area, maximum defect contrast (MDC) and defect volume, using automated three-dimensional quantitation. The differences between the two methods were less than 4% for defect-to-normal ARM ratio, 19% for MDC and 13% for defect volume. These differences are within the range of estimated statistical variation of SPET. The calculation times of the two methods were comparable. For all SPET studies, OSEM attenuation correction gave a more correct activity distribution, with respect to both the homogeneity of the radiotracer and the shape of the cardiac insert. The difference in uniformity between OSEM and Chang's method was quantified by segmental analysis and found to be less than 8% for the normal study. In conclusion, OSEM and Chang's attenuation correction are quantitatively equivalent, with comparable calculation times. OSEM reconstruction gives a more correct activity distribution and is therefore preferred.