Study of the effect of statistical fluctuations on defect detectability at clinical count levels in cardiac SPECT

Cardiac SPECT using Tl-201 suffers from low count statistics. Any statistical studies concerning the evaluation of a reconstruction algorithm, acquisition parameters, diagnostic confidence, etc., for clinical applications are impacted by the difficulty of obtaining data with multiple noise realizations. For this work, we acquired list-mode data of a Tl-201 cardiac phantom with very high counts in three configurations-with an anterior defect, an inferior defect, and no defect. The list-mode data were repartitioned to obtain statistically independent multiple data sets all with the same, clinically relevant noise level. Images were reconstructed from each of the resulting data sets using an iterative algorithm with attenuation correction. Reconstructed images were examined by four human observers, as well as analyzed quantitatively. The ability of observers to differentiate between normal scans and scans with defects varied substantially among datasets. There was correlation between the measured defect detectability and the visual assessment. The fact that the visibility of defects and the uniformity of normal scans varied significantly from one data set to the next, even when both were acquired at the same time, under identical conditions, indicates that the low statistics levels at clinical doses can have a measurable effect on diagnostic confidence.