1. From the Departments of Imaging Physics (M.C.J., D.D.C., R.R.L.), Interventional Radiology (E.N.K.C., D.L.B.), Diagnostic Radiology, Abdominal Imaging Section (E.P.T.), and Diagnostic Radiology, Neuroradiology Section (D.S.), The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030; and Radiology, Medical Physics Section (X.D.), University of Texas Southwestern Medical Center, Dallas, Tex.