The purpose of the study is to determine whether a new colonoscopic viewing technique called Linked color imaging(LCI) helps endoscopists detect more dysplasia lesions in ulcerative colitis patients than conventional colonoscopy using white light alone.

Patients with longstanding IBD have increased risk of colorectal cancer (CRC) compared to the general population. The association between duration of the disease and development of CRC is the rationale for endoscopic surveillance. Colonoscopic surveillance of ulcerative colitis patients has been shown to reduce the risk of colorectal cancer and allow detection at an earlier stage, but even with meticulous examination, some precancerous lesions or cancers are missed. The newly developed LCI system (FUJIFILM Co.) creates clear and bright endoscopic images by using short-wavelength narrow-band laser light combined with white laser light on the basis of BLI technology. LCI makes red areas appear redder and white areas appear whiter. Thus, it is easier to recognize a slight difference in color of the mucosa. This is a study to determine if using Linked color imaging (LCI) of the colon, rather than the usual white light on the colon, will improve the detection of more dysplasia lesions in ulcerative colitis.

Inclusion Criteria:patients with ulcerative colitis who meet surveillance criteria Exclusion Criteria:pregnant patients,unable or unwilling to give informed consent,patients with severe active colitis who would be unsafe to endoscope