Mark Holden, Derek L.G. Hill, Erika R. E. Denton¹ Jo M. Jarosz¹ Tim C. S. Cox² and David J. Hawkes
Radiological Sciences, GKT, Guy's Hospital, London, SE1 9RT, UK. ¹ Radiology Dept., King's College Hospital, London SE5 9RS, UK ² Institute of Neurology, UCL, Queen's Square, London WC1N 3BG, UK e-mail: mark.holden@kcl.ac.uk