Diffusion-Weighted Magnetic Resonance Imaging in Ileocolonic Crohn's Disease: Validation of Quantitative Index of Activity

OBJECTIVES: Magnetic resonance imaging (MRI) allows accurate assessment of Crohn's disease (CD), but requires gadolinium injection. Diffusion-weighted (DW)-MRI yields comparable performances in small bowel CD. We compared the accuracy of DW-MR enterocolonography (MREC) and the magnetic resonance index of activity (MaRIA), and performed an external validation of the Clermont score in assessing inflammation in CD. METHODS: This was an observational prospective study of a single-center cohort. A total of 130 CD patients underwent consecutively MREC with gadolinium injection and DWI sequences between July 2011 and December 2012. RESULTS: Of the 848 evaluated segments (small bowel = 352, colon/rectum = 496), 175 (20.6%) were active (small bowel = 111, colon/rectum = 64) defined as MaRIA >= 7. Using a receiver operating characteristic (ROC) curve, we determined an apparent coefficient of diffusion (ADC) threshold of 1.9x10(-3) mm(2)/s that yielded a sensitivity and a specificity in discriminating active from nonactive CD of 96.9% and 98.1%, respectively, for the colon/rectum, and 85.9% and 81.6%, respectively, for the ileum. ADC was better correlated to MaRIA >= 7 than related contrast enhancement obtained with injected sequences (P < 0.001). The Clermont score (= 1.646xbowel thickness - 1.321xADC + 5.61 3xedema + 8.306xulceration + 5.039) was highly correlated with the MaRIA (rho = 0.99) in ileal CD but not in colonic CD (rho < 0.80). Interobserver agreement was high with regard to ADC measurement (correlation > 0.9, P < 0.001, and concordance > 0.9, P < 0001). CONCLUSIONS: DW-MREC is a reliable tool to assess inflammation in colonic (ADC) and ileal (Clermont score) CD and its use in daily practice would avoid gadolinium injection.