1. From the Department of Anesthesiology and Critical Care and the Department of Radiology (M.C., Y.X., R.R.R.), University of Pennsylvania, Philadelphia, Pennsylvania; the Interdepartmental Division of Critical Care Medicine and Department of Medicine (A.G.) and Hospital for Sick Children (B.P.K., T.Y.), University of Toronto, Toronto, Ontario, Canada; the Departments of Anesthesia and Biomedical E