1. From the Departments of Radiology (J.D.R., J.M.B., S.P.S., J.G.F.), Colorectal Surgery (A.L.L.), and Gastroenterology (D.H.B.), Mayo Clinic, 200 First St SW, Rochester, MN 55905; and Department of Radiology, Mayo Clinic, Scottsdale, Ariz (C.O.M.).