[1] UCLH, Univ Coll London, Inst Nucl Med, Euston Rd T-5, London NW1 2BU, England
[2] Univ Coll London Hosp, Inst Nucl Med, Euston Rd T-5, London NW1 2BU, England
[3] UCL, Dept Comp Sci, Gower St, London WC1E 6BT, England
[4] UCL, Ctr Med Imaging, 250 Euston Rd, London NW1 2PG, England
[5] UCL, Ctr Med Imaging Comp, Gower St, London WC1E 6BT, England
[6] Univ Wollongong, Ctr Med Radiat Phys, Northfields Ave, Wollongong, NSW 2522, Australia