Objective: Lesion detection at contrast material-enhanced breast Magnetic Resonance (MR) imaging is primarily based on a lesion's vascularity relative to normal breast tissue. MR imaging may be still be advantageous because it can be used not only to characterize the lesion in question but also to evaluate the remainder of the breast, potentially leading to identification of unsuspected multifocal disease. The primary benefit of a noninvasive test such as MR imaging undertaken prior to tissue diagnosis (ie, with core biopsy or excisional biopsy) is that it can be used to determine which lesions are likely to be benign, so that mammographic or clinical followup could be used in place of tissue diagnosis. When a test is used in this capacity, it must be sufficiently sensitive that the negative predictive value is very high without sacrificing specificity. Standard evaluation criteria have not been optimized for evaluating