1. Gastrointestinal Services, University College London Hospitals NHS Foundation Trust, London, UK
2. Eastman Dental Institute, University College London, London, UK
3. UCL Medical School, University College London, London, UK
4. Department of Radiology, University College London Hospital, London, UK
5. Division of Medicine, University College London, London, UK
6. Gastrointestinal Services, University College London Hospitals NHS Foundation Trust, Ground Floor West, 250 Euston Road, London, NW1 2PG, UK