1. Department of Radiology, Washington University School of Medicine, Saint Louis, Missouri 63110, United States
2. Center for Mass Spectrometry and Metabolic Tracing, Department of Chemistry, Department of Medicine, Washington University, Saint Louis, Missouri 63130, United States
3. Departments of Neurology, Neuroscience, Physical Therapy and Occupational Therapy, Washington University School of Medicine, Saint Louis, Missouri 63110, United States