The aim:1) To test the correlation of pCLE-obtained features with histological findings in UC; comparing the real-time conventional colonoscopy Baron score with CLE assessment. 2) To test the accuracy of the investigators previously proposed simplified four-grade classification system of crypt architecture in evaluating inflammation activity in UC by pCLE.

Patients with acute inflammatory infiltrates seen on histological assessment are more likely to experience relapse than are those without infiltrates,studies suggest that severity of inflammation is a risk factor for colorectal neoplasia in UC.

The assessment of inflammation activity by conventional colonoscopy is inaccurate in the prediction of acute inflammation in some cases. Confocal laser endomicroscopy (CLE) allows for real-time endoscopy and histological diagnosis of gastrointestinal diseases. In our previous study, we confirmed a simplified four-grade classification system of crypt architecture(Grade A :normal; Grade B: an irregular arrangement of colonic crypts with normal size and shape, and enlarged spaces between crypts; Type C: an enlarged crypt opening and a more irregular crypt arrangement than type B; Type D: crypt destruction and / or crypt abscess) by eCLE in predicting acute inflammation, and found a good correlation with histology. In this study, the investigators aimed to test the accuracy of the proposed tne four-grade classification system in evaluating inflammation activity in UC by pCLE.

Inclusion Criteria:

• Male or Female aged 18-80;
• patients previously or in-process diagnosed as Ulcerative Colitis

Exclusion Criteria:

• Patients with gastrectomy, acute GI bleeding, and advanced esophageal cancer;
• Patients under conditions unsuitable for performing CLE including coagulopathy (prothrombin time <50% of control, partial thromboplastin time >50 s), lactation, food retention, oesophageal stenosis, postoperative cases, leiomyoma, impaired renal function (creatinine level >1.2 mg/dL), pregnancy or breastfeeding, and known allergy to fluorescein sodium;
• Inability to provide informed consent and other situations that could interfere with the examination protocol.

Consecutive patients screened that fulfill the eligibility criteria at Qilu Hospital, Shandong University will be enrolled into the study