From the Department of Radiology (H.H.
S.J.K., M.I., Y.X., K.E., B.H., H.S., D.G., W.G., R.R.R.), Department of Anesthesiology and Critical Care (M.C.), and Pulmonary, Allergy and Critical Care Division (M.D.R.), University of Pennsylvania, 308 Stemmler Hall, 3450 Hamilton Walk, Philadelphia, PA 19104.