1 Division of Surgery and Interventional Sciences, Gastrointestinal Services Department, University College London, University College London Hospitals NHS Foundation Trust, London, UK. m.chand@ucl.ac.uk.
2 Department of Surgery and Interventional Sciences, University College London Hospitals, NHS Trusts, GENIE Centre, University College London, 235 Euston Rd, London, NW1 2BU, UK. m.chand@ucl.ac.uk.
3 Radiology Department, University College London Hospitals, NHS Foundation Trust, London, UK.
4 Division of Engineering, University College London, London, UK.
5 Division of Surgery and Interventional Sciences, Gastrointestinal Services Department, University College London, University College London Hospitals NHS Foundation Trust, London, UK.