[1] Mayo Clin, Coll Med, Dept Radiol, Rochester, MN 55905 USA
[2] Univ Minnesota, Sch Med, Ctr Magnet Resonance Res, Minneapolis, MN 55455 USA
[3] Mayo Clin, Coll Med, Dept Neurol, Rochester, MN 55905 USA
[4] Univ Minnesota, Sch Med, Dept Radiol, Minneapolis, MN 55455 USA
[5] Mayo Clin, Coll Med, Dept Neurosci, Rochester, MN 55905 USA
[6] Mayo Clin, Coll Med, Dept Biochem Mol Biol, Rochester, MN 55905 USA