1. From the National Research Council, Institute of Clinical Physiology Metabolism and MRI Laboratory (A.M.S., A.G., D.C., V.P., E.B., S.G., S.T., M.L.), Pisa; National Research Council, Institute of Biomedical Engineering (A.M.), Padova; and Department of Internal Medicine (E.F.), University of Pisa School of Medicine, Pisa, Italy.