Abstract
We developed an approach to receiver operating characteristic(ROC)analysis that employs the mean and standard deviation of CT vaules for measuring density detection by CT scanner. A CT phantom(PPE resin)for evaluating low-contrast detectability was imaged for case samples. The mean and standard deviation of CT values within regions of interest(ROIs)that were set in a simulated nodule within the CT phantom were used as actually positive data. The values in ROIs of the same size in the same images that did not contain a nodule were used as actually negative data. Density detectability was summarized by the ROC area index Az. Detectabilities were measured with two types of CT scanners for varying absorbed doses. From the experimental results, there were statistically significant differences in density detectability between the several combinatons of exposed dose. We conclude that our new method is useful for measuring density detectability and is correlated with the results obtained from observer-performance study of low-contrast detectability. Furthermore, our method offered better performance in detecting statistically significant differences than the observer performance study.
