1. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, P. R. China
2. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. Department of Radiology, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, P. R. China
4. National Engineering Research Center for Nanotechnology, Shanghai 200241, P. R. China