1. Department of General Surgery, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266011, China
2. Department of Gastrointestinal Surgery, The Affiliated Hospital of Binzhou Medical University, Binzhou, Shandong 256603, China
3. Department of Ultrasound, The 3rd Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong 510630, China
4. Centers for Disease Control and Prevention of Binzhou City, Binzhou, Shandong 256603, China
5. Center of Colon and Rectum, Qingdao Municipal Hospital, Qingdao, Shandong 266011, China