1. Department of Materials Science and Engineering; College of Engineering; Peking University; Beijing 100871 China
2. Institute of Medical Physics; Key Laboratory of Particle & Radiation Imaging; Ministry of Education; Department of Engineering Physics; Tsinghua University; Beijing 100084 China
3. Department of Biomedical Engineering; College of Engineering; Peking University; Beijing 100871 China
4. Department of Radiology; Affiliated Hospital of the Academy of Military Medical Sciences; Beijing 100071 China
5. Synthetic and Functional Biomolecules Center; Department of Chemical Biology; College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 China