1Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 2Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 3Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 4Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 5Center for Molecular and Biomolecular Imaging, Duke University, Durham, NC, United States