[1] Univ London Imperial Coll Sci Technol & Med, Sch Med, Natl Heart & Lung Inst, London SW3 6NP, England
[2] Univ London Imperial Coll Sci Technol & Med, Sch Med, Div Investigat Sci, London SW3 6NP, England
[3] Royal Brompton Hosp, Dept Radiol, London SW3 6NP, England