1. From the Department of Radiology (B.P.P., H.H.G.) and Division of Pulmonology, Allergy, and Critical Care Medicine, Department of Medicine (D.K.D., B.S., H.B.), Stanford University School of Medicine, 300 Pasteur Dr, S072, Stanford, CA 94305; Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, MA (K.E.S.); and Division of Pulmonary and Critical Care Medicine, Massachusetts General Hospital, Boston, MA (K.E.S.).