Examining Techniques on Adenoma Miss Rate in Proximal Colon

Inclusion Criteria: * Patients between 45 and 80 years who undergo colonoscopy examination for screening, and who receive primary screening and get positive result Exclusion Criteria: * Pregnant female patients * Patients received colonoscopy in the past 5 years * Patients who have history of colorectal cancer, colorectal polyposis, inflammatory bowel disease or heredity colorectal neoplasm syndrome such as familiar adenomatous polyposis, Lynch Syndrome and so on * Patients who had previous abdominal surgery * Patients who are known to have colonic stricture or obstructing tumor from the results of radiography (X ray, CT scan or barium enema) * Patients who are presenting acute surgical conditions such as severe colitis, megacolon and active gastrointestinal bleeding * Patients who have inadequate bowel preparation * Patients who reject to participate in this study