1. From the Cardiovascular Magnetic Resonance Unit (P.K., M.A.T., J.P., D.W., J.T., M.A.W., L.J.A., D.J.P.) and Medical Statistics Department (M.R.), Imperial College and Royal Brompton Hospital, and Department of Hematology (J.B.P.) and Hatter Cardiovascular Institute (J.M.W.), University College London, London, UK.