1. Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
2. Department of Radiology, The University of Tokyo hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
3. Graduate School of Biomedical Sciences, Tokushima University, 3-18-15, Kuramoto-cho, Tokushima, Japan