Effect of AsF-TCT duration on estimation of defect size and severity in cardiac SPECT imaging

Attenuation correction (AC) based on short, sequential asymmetric fan-beam TCTs has been demonstrated to improve the uniformity of normal cardiac SPECT images. The purpose of this study was to assess whether AC from short AsF-TCTs also improves semi-quantitative estimates of lesion size and severity for SPECT studies of abnormal myocardium. An anthropomorphic cardiac-thorax phantom was used to acquire Tl-201 SPECT studies of a 45° transmural defect with activity 0-75% of normal tissue. ECTs of the cardiac insert were obtained with the insert inside the thorax phantom and in air for 16 defect configurations and corrected with attenuation maps derived from 1-20 minute TCTs. Defect size was measured where the activity profile decreased below 75% of that of normal tissue, and defect severity was assessed by the ratio of activity in a ROI inside the defect to that of known normal regions of the myocardium. Without AC, defects in the septal wall show the greatest size increases because they appear to extend into the inferior wall. AC based on four minute AsF-TCTs improves defect size to 75-110% relative to in-air measurements. Anterior-wall defects show the smallest changes after correction. AC alters defect severity by less than 15%, but yields improved contrast between adjacent normal and defect regions