Influence of the grayscale on phantom-based image quality assessment in x-ray computed tomography

Radiation dose associated with CT scans has become an important concern in medical imaging. Fortunately, there are many pathways to reducing dose. A complicated aspect, however, is to ensure that image quality is not affected while reducing the dose. A preferred method to assess image quality is ROC analysis, possibly with a search process. For early assessment of new imaging solutions, utilization of human observers and real patient data is rarely practical. Instead, studies involving phantoms and model observers are often preferred. We present here an experimental result that sheds light on how the grayscale window affects human observer performance in a typical phantom-based study; and we also present an analysis that clarifies how the grayscale window affects the statistics of the image. These studies provide a better understanding of possible consequences associated with not including a grayscale window in studies with model observers, as is typical.