1. Gastroenterological Center, Yokohama City University Medical Center, Yokohama, Japan
2. Department of Gastroenterology, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
3. Ultrasound Systems Engineering, GE Healthcare Japan Corporation, Hino-shi, Japan
4. Department of Mechanical and Intelligent Systems Engineering, Graduate School of Informatics and Engineering, School of Informatics and Engineering, The University of Electro-Communications, Choufu-shi, Japan