Lesion detection and signal–to–noise ratio in CT images

This study measured observers' ability to detect and locate focal lesions on simulated CT images. The difficulty of the detection task was manipulated by changing the difference in attenuation between the lesion and its background (contrast), the random variation in the CT values (noise) or the lesion's size. The human observers' performance was compared to that of matched filter detector, modified to include the effects introduced by the display window and the uncertainty about the lesion's location on the image. Changes in lesion contrast, lesion size and noise produced large variations in both the lesion signal-to-noise ratio (a measure of the matched filter detector's performance) and estimated measures of the observer's detection and localization ability. Changes in observers' performance were closely related to changes in lesion signal-to-noise ratio. Generally, changes in lesion contrast, lesion size or noise that produced similar values of lesion signal-to-noise ratios had equivalent effects upon the observers' performance.