1. From the Departments of Radiology (J.S., R.J.B., E.A.S., S.B.R.), Obstetrics and Gynecology (E.A.S.), Medical Physics (S.B.R.), Biomedical Engineering (S.B.R.), Medicine (S.B.R.), and Emergency Medicine (S.B.R.), University of Wisconsin, 600 Highland Ave, Madison, WI 53792.