Comparison of ordered subsets expectation maximization and Chang's attenuation correction method in quantitative cardiac SPET: A phantom study

Photon attenuation is one of the primary causes of artifacts in cardiac sin gle photon emission tomography (SPET). Several attenuation correction algor ithms have been proposed. The aim of this study was to compare the effect o f using the ordered subsets expectation maximization (OSEM) reconstruction algorithm and Chang's non-uniform attenuation correction method on quantita tive cardiac SPET. We performed SPET scans of an anthropomorphic phantom si mulating normal and abnormal myocardial studies. Attenuation maps of the ph antom were obtained from computed tomographic images. The SPET projection d ata were corrected for attenuation using OSEM reconstruction, as well as Ch ang's method. For each defect scan and attenuation correction method, we ca lculated three quantitative parameters: average radial maximum (ARM) ratio of the defect-to-normal area, maximum defect contrast (MDC) and defect volu me, 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 es timated statistical variation of SPET. The calculation times of the two met hods were comparable. For all SPET studies, OSEM attenuation correction gav e a more correct activity distribution, with respect to both the homogeneit y of the radiotracer and the shape of the cardiac insert. The difference in uniformity between OSEM and Chang's method was quantified by segmental ana lysis and found to be less than 8% for the normal study in conclusion, OSEM and Chang's attenuation correction are quantitatively equivalent, with com parable calculation times. OSEM reconstruction gives a more correct activit y distribution and is therefore preferred. ((C) 1998 Lippincott Williams & Wilkins).