From the Department of Medicine, University of North Carolina School of Medicine, Chapel Hill (R.J.F.); and the Departments of Radiology (J.S.H.), Medicine (A.Z.F.), and Pathology (I.A.R.), Massachusetts General Hospital, and the Departments of Radiology (J.S.H.), Medicine (A.Z.F.), and Pathology (I.A.R.), Harvard Medical School - both in Boston.