Objective Magnetic resonance imaging (MRI) enables accurate assessment of inflammatory bowel diseases (IBD), but its main limitation is the need for bowel preparation. Diffusion-weighted imaging is feasible in Crohn's disease. We evaluated the accuracy of MRI in combination with diffusion-weighted imaging (DWI-MRI) without oral or rectal preparation in assessing colonic inflammation in both ulcerative colitis and Crohn's disease.

Design This was an observational study of a single-centre cohort.

Patients All patients who underwent DWI-MRI-colonography without bowel preparation between January 2008 and February 2010 in our centre were analysed.

Results Among the 96 patients (ulcerative colitis=35; Crohn's disease=61) who had DWI-MRI-colonography, 68 had concomitant endoscopy. In ulcerative colitis a segmental magnetic resonance score (MR-score-S) >1 detected endoscopic inflammation with a sensitivity and specificity of 89.47% and 86.67%, respectively (AUROC=0.920, p=0.0001). In the Crohn's disease group, a MR-score-S >2 detected endoscopic inflammation in the colon with a sensitivity and specificity of 58.33% and 84.48%, respectively (AUROC=0.779, p=0.0001). The MR-score-S demonstrated better accuracy for the detection of endoscopic inflammation in the ulcerative colitis group than in the Crohn's disease group (p=0.003). In ulcerative colitis, the proposed total magnetic resonance score (MR-score-T) correlated with the total modified Baron score (r=0.813, p=0.0001) and the Walmsley index (r=0.678, p<0.0001). In Crohn's disease, the MR-score-T correlated with the simplified endoscopic activity score for Crohn's disease (r=0.539, p=0.001) and the Crohn's disease activity index (r=0.367, p=0.004). The DWI hyperintensity was a predictor of colonic endoscopic inflammation in ulcerative colitis (OR=13.26, 95% CI 3.6 to 48.93; AUROC=0.854, p=0.0001) and Crohn's disease (OR=2.67, 95% CI 1.25 to 5.72; AUROC=0.702, p=0.0001). The accuracy of the DWI hyperintensity for detecting colonic inflammation was greater in ulcerative colitis than in Crohn's disease (p=0.004).

Conclusions DWI-MRI-colonography without bowel preparation is a reliable tool for detecting colonic inflammation in ulcerative colitis.