1. Division of Gastroenterology and Hepatology, Graduate School of Medical and Dental Sciences, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata-City, Niigata 951-8510, Japan
2. Department of Gastroenterology, Saiseikai Kawaguchi General Hospital, 5-11-5 Nishikawaguchi, Kawaguchi-City, Saitama 332-8558, Japan
3. Department of Endoscopy, Niigata University Medical and Dental Hospital, 1-757 Asahimachi-dori, Chuo-ku, Niigata-city, Niigata 951-8510, Japan
4. Division of Digestive and General Surgery, Graduate School of Medical and Dental Sciences, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata-City, Niigata 951-8510, Japan
5. Department of Gastroenterology, Nagaoka Red Cross Hospital, 2-297-1 Sensyu, Nagaoka-City, Niigata 940-2085, Japan
6. Department of Gastroenterology, Niigata Cancer Center Hospital, 2-15-3 Kawagishicho, Chuo-ku, Niigata-City, Niigata 951-8566, Japan