1 Departments of Cardiology and Radiology, Royal Brompton Hospital, London, UK; Department of Biomedical Engineering and Imaging Sciences, King's College, London, UK. Electronic address: e.nicol@nhs.net.
2 BHF Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, UK. Electronic address: Michelle.williams@ed.ac.uk.
3 Knight Cardiovascular Institute, Oregon Health & Science University, Portland, OR 97239, USA. Electronic address: ferencik@ohsu.edu.