[1] Mayo Clin, Dept Physiol & Biophys, Physiol Imaging Res Lab, Rochester, MN 55905 USA
[2] Univ Western Ontario, Dept Appl Math, London, ON N6A 5B9, Canada
[3] Univ Western Ontario, Dept Med Biophys, London, ON N6A 5B9, Canada
[4] Mayo Clin, Div Endocrinol Diabet Metab Nutr & Internal Med, Rochester, MN USA
[5] Childrens Hosp Los Angeles, Los Angeles, CA 90027 USA