1. From the Departments of Radiology (L.F.A., C.J.O., D.M.S., M.J.C., A.M.M., M.P.C.) and Vascular Surgery (Y.M.E.), Mayo Clinic, 4500 San Pablo Rd, Jacksonville, FL 32224; and Department of Radiology, University of Alabama Birmingham, Birmingham, Ala (M.L.R.).