1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Innovation Academy of Precision Measurement Science and Technology, Chinese Academy of Sciences-Wuhan National Laboratory for Optoelectronics, Wuhan 430071, P. R. China
2. University of Chinese Academy of Sciences, Beijing, P. R. China
3. Department of Radiology, Chinese PLA General Hospital, Beijing, P. R. China
4. California Nano Systems Institute, Jonsson Comprehensive Cancer Center, The Molecular Biology Institute, Department of Chemistry and of Bioengineering, University of California, Los Angeles, California, United States