1. Department of Diabetes & Endocrinology, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield S10 2JF, UK
2. Department of Diabetes & Endocrinology, University College London Hospital NHS Foundation Trust, London NW1 2BU, UK
3. Centre for Obesity & Metabolism, Department of Experimental & Translational Medicine, Division of Medicine, University College London, London WC1N 3BG, UK
4. Wellcome/EPSRC Centre for Interventional and Surgical Sciences, University College London, London WC1E 6BT, UK
5. Department of Medical Physics and Biomedical Engineering, University College London, London WC1E 6BT, UK
6. Department of Neurosurgery, National Hospital for Neurology and Neurosurgery, London WC1N 3BG, UK