1. Department of Gastroenterology, People's Hospital of Leling City, Dezhou, Shandong 253600, P.R. China
2. Department of General Surgery, Zhucheng People's Hospital, Weifang, Shandong 262200, P.R. China
3. Department of Gastroenterology, Qiqihar Jianhua Hospital, Qiqihar, Heilongjiang 161000, P.R. China
4. Second Department of General Surgery, Tianjin Fifth Central Hospital, Tianjin 300450, P.R. China
5. Department of Gastroenterology, No. 215 Hospital of Shaanxi Nuclear Industry, Xianyang, Shaanxi 712000, P.R. China