[1] Massachusetts Gen Hosp, Dept Neurol, Boston, MA 02114 USA
[2] Massachusetts Gen Hosp, Dept Radiol, Boston, MA 02114 USA
[3] Univ Calif San Francisco, Dept Neurol, San Francisco, CA 94143 USA
[4] Natl Inst Neurol Disorders & Stroke, Bethesda, MD USA
[5] Univ Fed Sao Paulo, Dept Neurol & Neurosurg, Sao Paulo, Brazil