[1] UCL, Div Surg & Intervent Sci, Charles Bell House,43-45 Foley St, London W1W 7TS, England
[2] Univ Coll London Hosp NHS Trust, Dept Radiol, 235 Euston Rd, London NW1 2BU, England
[3] Univ Coll London Hosp NHS Trust, Dept Urol, 235 Euston Rd, London NW1 2BU, England