1. From the Departments of Radiology (R.L.W., A.M.P., J.H.W., H.K.S., A.C.W., F.W.W.), Cardiology (E.R.M., J.D.H.), Neurosurgery (E.L.Z.), and Vascular Surgery (R.M.F., M.A.G., O.C.V., J.P.C.), University of Pennsylvania Medical System, Philadelphia; and Children’s Hospital of Philadelphia (S.L.W.), Penn.