Radiological images constitute a special class of images that are captured (or computed) for a specific purpose (i.e. diagnosis) and their "correct" interpretation is vitally important. However, because they are not "natural " images, radiologists must be trained to visually interpret them. This training involves perceptual learning that is gradually acquired over an extended period of exposure to radiological images. This implicit (subconscious) knowledge is difficult to pass along explicitly (i.e. verbally) to less experienced radiologists. Multimedia technology has the potential to facilitate perceptual learning in new radiologists. However, it is important to have an objective and quantitative method for evaluating the progress of trainees using this approach. This paper proposes an eye-tracker-based metric for determining the level of expertise of a radiologist in training, based on where he/she lies along a scale based on the visual scanning behavior of radiologists, ranging from novice to expert.