[1] Washington Univ, Dept Chem, St Louis, MO 63110 USA
[2] Washington Univ, Sch Med, Biomed MR Lab, St Louis, MO 63110 USA
[3] Washington Univ, Dept Radiol, St Louis, MO 63110 USA
[4] Washington Univ, Dept Neurol, St Louis, MO 63110 USA
[5] Washington Univ, Dept Pharmacol & Mol Biol, St Louis, MO 63110 USA
[6] Acad Sinica, Inst Biomed Sci, Taipei, Taiwan
[7] Natl Yang Ming Univ, Dept Biomed Engn, Taipei, Taiwan