1 1 Acute Stroke Programme, Department of Medicine and Clinical Geratology, Oxford University Hospitals NHS Trust, Oxford, UK.
2 2 Acute Stroke Programme, Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
3 3 Medical Sciences Division, University of Oxford, Oxford, UK.
4 2 Acute Stroke Programme, Radcliffe Department of Medicine, University of Oxford, Oxford, UK3 Medical Sciences Division, University of Oxford, Oxford, UK4 Acute Vascular Imaging Centre, University of Oxford, Oxford University Hospitals, Oxford, UK alastair.buchan@medsci.ox.ac.uk.