1. Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
2. Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
3. Institute for Translational Medicine and Therapeutics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
4. Department of Process Research and Development, Merck Research Laboratories, Kenilworth, New Jersey 07033, United States
5. Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States