Assessment of medical imaging systems and computer aids: a tutorial review.

This article reviews the central issues that arise in the assessment of diagnostic imaging and computer-assist modalities. The paradigm of the receiver operating characteristic (ROC) curve--the dependence of the true-positive fraction versus the false-positive fraction as a function of the level of aggressiveness of the reader/radiologist toward a positive call--is essential to this field because diagnostic imaging systems are used in multiple settings, including controlled laboratory studies in which the prevalence of disease is different from that encountered in a study in the field. The basic equation of statistical decision theory is used to display how readers can vary their level of aggressiveness according to this diagnostic context. Most studies of diagnostic modalities in the last 15 years have demonstrated not only a range of levels of reader aggressiveness, but also a range of level of reader performance. These characteristics require a multivariate approach to ROC analysis that accounts for both the variation of case difficulty and the variation of reader skill in a study. The resulting paradigm is called the multiple-reader, multiple-case ROC paradigm. Highlights of historic as well as contemporary work in this field are reviewed. Many practical issues related to study design and resulting statistical power are included, together with recent developments and availability of analytical software.