1. Gordon Center for Medical Imaging, Massachusetts General Hospital and Harvard Medical School, 3rd Avenue, Charlestown, Massachusetts 02129, United States
2. Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, United States
3. Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts 02115, United States
4. Department of Pharmacology, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, North Carolina 27599, United States