1. Laboratory of Magnetic Resonance Spectroscopy and Imaging, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, P. R. China
2. School of Pharmacy, Xi’an Jiaotong University, Xi’an 710061, P.R. China
3. Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55455, United States