[1] Mayo Clin, Dept Radiol, 200 1st St SW, Rochester, MN 55905 USA
[2] Mayo Clin, Dept Neurosurg, Rochester, MN USA
[3] Mayo Clin, Div Prevent Med, Rochester, MN USA
[4] Mayo Clin, Knowledge & Evaluat Res Unit, Rochester, MN USA
[5] Mayo Clin, Dept Neurol, Rochester, MN USA
[6] Univ Calgary, Dept Clin Neurosci, Hotchkiss Brain Inst, Foothills Hosp,Cumming Sch Med, Calgary, AB, Canada