1. Medical Research Center, Academia Sinica, Nankang 11529, Taipei, Taiwan.
2. Institute of Physics, Academia Sinica, Nankang 11529, Taipei, Taiwan.
3. Department of Materials Science, Pohang University of Science and Technology, Pohang, Korea.
4. Department of Radiology, College of Medicine, College of Dentistry, Yonsei University, Seoul, Korea.
5. Department of Periodontology, College of Dentistry, Yonsei University, Seoul, Korea.
6. IPA - Ecole Polytechnique Federale de Lausanne, CH-1015, Lausanne, Switzerland.