1. The
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia 30332, United States
2. Department
of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China
3. Department
of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110, United States
4. Laboratory
of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, P. R. China