1. Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892, United States
2. Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20982, United States
3. Department of Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, United States
4. Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, United States
5. National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States