[1] Johns Hopkins Univ Hosp, Div Neurosci Crit Care Med, Baltimore, MD 21287 USA
[2] Johns Hopkins Univ, Sch Med, Dept Radiol, Baltimore, MD 21205 USA
[3] Johns Hopkins Univ, Sch Med, Dept Neurosurg, Baltimore, MD 21205 USA
[4] Johns Hopkins Univ, Sch Med, Dept Neurol, Baltimore, MD 21205 USA
[5] Johns Hopkins Univ, Sch Med, Dept Anesthesiol & Crit Care Med, Baltimore, MD 21205 USA