[1] UCL, Div Surg & Intervent Sci, London, England
[2] Univ Coll London Hosp, Dept Radiol, London, England
[3] Univ Coll London Hosp, Dept Histol, London, England
[4] Royal Coll Surgeons England, London WC2A 3PN, England
[5] London Sch Hyg Ad Trop Med, Clin Effectiveness Unit, London, England