1. Department of Gastroenterology, Beijing Ditan Hospital, Capital Medical University, No. 8 Jingshun East St., Chaoyang District, Beijing 100015, China
2. The Endoscopy Center, Huangshan Shoukang Hospital, Meilin Rd. Economic & Technological Development Zone, Huangshan, Anhui Province 245000, China
3. Department of Gastroenterology, Huairou Hospital, Qingchun Rd., Huairou, Beijing 101400, China