1 Department of Radiology, Seattle Children's Hospital, University of Washington School of Medicine, Seattle, WA.
2 Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA.
3 Departments of Radiology and Medicine, Pulmonary Division, Boston Children's Hospital and Harvard Medical School, Boston, MA.
4 Department of Radiology, Seattle Children's Hospital, University of Washington School of Medicine, Seattle, WA. Electronic address: grace.phillips@seattlechildrens.org.