1. Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan
2. Center for Advanced Medical Engineering Research & Development (CAMED), Kobe University, 1-5-1 Minatojimaminami-machi, Chuo-ku, Kobe, Hyogo 650-0047, Japan