1. From the Department of Radiology, Northwestern University Feinberg School of Medicine, 676 N St Clair St, Suite 800, Chicago, IL 60611 (K.R.D., M.B.P., S.M.S., M.F.E., R.S., R.J.L.); and Department of Radiology, U of C School of Medicine, Aurora, Colo (R.K.R.).