PIRADS: Well defined. BI-RADS: Mammo: At least 75% of the margin is sharply demarcated, with an abrupt transition between the lesion and surrounding tissue (historically, "well defined" or "sharply defined"). MRI: Entire margin is sharply demarcated with abrupt transition between the lesion and surrounding tissue (historically, "smooth"). US: Entire margin is well defined or sharp, with an abrupt transition between the lesion and surrounding tissue (historically, "well defined" or "sharply defined").