[1] Walter Reed Army Med Ctr, Dept Med, Washington, DC 20307 USA
[2] George Washington Univ, Med Ctr, Dept Neuroradiol, Washington, DC 20052 USA
[3] Pulm Crit Care & Sleep Med Serv, Washington, DC USA
[4] Uniformed Serv Univ Hlth Sci, Dept Med, Bethesda, MD 20814 USA