1. State Key Laboratory of Tribology Department of Mechanical Engineering Tsinghua University Beijing 100084 China
2. Department of Radiology Beijing Tsinghua Changgung Hospital School of Medicine Tsinghua University Beijing 102218 China
3. The Center for Biomedical Imaging Research Department of Biomedical Engineering School of Medicine Tsinghua University Beijing 100084 China
4. State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and Engineering Tsinghua University Beijing 100084 China