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, UK 3 Medical Sciences Division, University of Oxford, Oxford, UK 4 Acute Vascular Imaging Centre, University of Oxford, Oxford University Hospitals, Oxford, UK alastair.buchan@medsci.ox.ac.uk.