[1] UCL Inst Neurol, Queen Sq MS Ctr, London, England
[2] Natl Hosp Neurol & Neurosurg, Lysholm Dept Neuroradiol, London, England
[3] London Sch Hyg & Trop Med, Med Stat Unit, London, England
[4] NIHR Univ Coll London Hosp Biomed Res Ctr, London, England