Diffusion-weighted magnetic resonance imaging in ileocolonic Crohn's disease: validation of quantitative index of activity

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.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.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 1.9 × 10(-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 (P0.001). The Clermont score (=1.646 × bowel thickness-1.321 × ADC+5.613 × edema+8.306 × ulceration+5.039) was highly correlated with the MaRIA (rho=0.99) in ileal CD but not in colonic CD (rho0.80). Interobserver agreement was high with regard to ADC measurement (correlation0.9, P0.001, and concordance0.9, P0001).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.