1. Department of Surgical Oncology, Graduate School of Medicine, Tohoku University 1-1, Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan
2. Department of Bioengineering and Robotics, Graduate School of Engineering, Tohoku University, Sendai, Japan
3. Biomedical Engineering Research Organization, Tohoku University, Sendai, Japan