[1] Univ Oxford, John Radcliffe Hosp, Acute Vasc Imaging Ctr, Biomed Res Ctr, Oxford OX3 9DU, England
[2] Oxford Radcliffe NHS Trust, Dept Med & Clin Geratol, Acute Stroke Programme, Oxford, England
[3] Univ Oxford, Nuffield Dept Med, Oxford, England
[4] John Radcliffe Hosp, Biomed Res Ctr, Dept Neuroradiol, Oxford OX3 9DU, England