Patient-specific Channelized Hotelling observer to estimate lesion detectability in CT.

Task-based image quality assessment is essential for CT protocol and radiation dose optimization. Despite many ongoing efforts, there is still an unmet need to measure and monitor the quality of images acquired from each patient exam. In this work, we developed a patient-specific channelized Hotelling observer (CHO)-based method to estimate the lesion detectability for each individual patient scan. The ensemble of background was created from patient images to include both relatively uniform regions and anatomically varying regions. Signals were modelled from lesions of different sizes and contrast levels after incorporating the effect of contrast-dependent spatial resolution. Index of detectability (d') was estimated using a CHO framework. This method was applied to clinical patient images obtained from a CT scanner at 3 different radiation dose levels. The d' for 5 different lesion size/contrast conditions was calculated across the scan range of each patient exam. The average noise levels and the d' averaged from 5 conditions were 13.2/3.78, 17.1/2.93 and 21.9/2.43 at 100%, 50% and 25% dose levels, respectively.