1. Department of Gastroenterology, Fukushima Medical University School of Medicine, Fukushima, Japan
2. Department of Endoscopy, Fukushima Medical University Hospital, Fukushima, Japan
3. Department of Hepato-Biliary-Pancreatic and Transplant Surgery, Fukushima Medical University School of Medicine, Fukushima, Japan
4. Division of Gastroenterology, Tohoku University Graduate School of Medicine, Sendai, Japan