Abstract: Objective To evaluate the diagnostic value of magnetic resonance colonography (MRC) combined with fecal calprotectin (FC) in the activity degree of ulcerative colitis (UC). Methods Forty-one patients with active UC were collected as the case group, and they were subdivided into mild and moderate active group (n=12) and severe active group (n= 29) according to the mayo endoscopic score(MES).During the same period, 32 healthy subjects were used as the control group. According to MES, 192 sections of intestine after colonoscopy were divided into normal segment group (n=39), mild and moderate active segment group (n=45) and severe active segment group (n=108). The thickness and the signal intensity anterior and posterior enhanced of the intestinal wall of each segment were measured, and edema of the intestinal wall, enlarged lymph nodes or comb sign were evaluated. The simplified MRC index (MRC-S) was obtained by Logistic regression analysis. The ROC curve was drawn to analyze the optimal threshold value of MRC-S for the diagnosis of intestinal segment lesions. FC concentration was measured in control group and case group. ROC curve was used to analyze the optimal threshold value for FC diagnosis of lesion activity. The diagnostic efficacy of MRC-S, FC and their combination were analyzed on UC lesion activity. Results The mean value or occurrence frequency of MRC parameters were higher in the mild and moderate group and severe active bowel group than those in the normal bowel group (P＜0.05). There were no significant differences in intestinal wall thickness between the severe active bowel group and the mild and moderate active bowel group. The diagnostic values of MRC-S in both active (MRC-S≥1) and severely active (MRC-S≥2) bowel lesions were higher (AUC was 0.979 and 0.881, respectively). The diagnostic values of FC were higher in both active (FC≥92.9 μg/g) and severely active (FC≥3 003.8 μg/g) UC patients (AUC was 1.000 and 0.958, respectively). MRC-S combined with FC showed obvious diagnostic specificity for patients with severe active UC (91.7%). Conclusion Both MRC-S and FC have a high value in the diagnosis of the disease activity in UC patients.The combination of the two of them can further improve the specificity of diagnosis.

Key words: magnetic resonance imaging, colitis, ulcerative, fecal calprotectin, degree of activity