1. Department of Endoscopy, Yuexi Hospital of the Sixth Affiliated Hospital, Sun Yat-sen University, Xinyi, Guangdong, P. R. China
2. Department of Endoscopic Surgery, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, P. R. China
3. Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, P. R. China