1. Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
2. Britton Chance Laboratory of Redox Imaging, Johnson Research Foundation, Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
3. University of Amsterdam, Amsterdam School of Communications Research (ASCoR), Netherlands
4. Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics Huazhong, University of Science and Technology, Wuhan 430074, P. R. China
5. Institute for Scientific Information — Thomson Reuters, Philadelphia, PA 19130, USA