1. State Key Laboratory of High Performance Ceramics and Superfine Microstructures; Shanghai Institute of Ceramics; Chinese Academy of Sciences; Shanghai 200050 P. R. China
2. Department of Radiology; Cancer Hospital/Institute and Department of Oncology; Shanghai Medical College; Fudan University; Shanghai 200032 P. R. China
3. Department of Materials Science and Engineering; Stanford University; Stanford CA 94305 USA