1. Department of Gastroenterology, Qingdao University Affiliated Qingdao Municipal Hospital, Qingdao, Shandong 266071, P.R. China
2. Department of Gastroenterology, Qingdao Municipal Hospital, Qingdao, Shandong 266071, P.R. China
3. Digestive Endoscopy Center, Department of Gastroenterology, Changhai Hospital, Shanghai 200433, P.R. China