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Objective: Assessment of disease extension and activity is crucial to guide treatment in Crohn's disease. The objective of the current cross-sectional study was to determine the accuracy of MR for this assessment. Design: 50 patients with clinically active (n = 35) or inactive (n = 15) Crohn's disease underwent ileocolonoscopy (reference standard) and MR. T2-weighted and precontrast and postcontrast-enhanced T1-weighted sequences were acquired. Endoscopic activity was evaluated by CDEIS (Crohn's Disease Endoscopic Index of Severity); in addition endoscopic lesions were classified as absent, mild (inflammation without ulcers) or severe (presence of ulceration). Results: The comparison of intestinal segments with absent, mild and severe inflammation demonstrated a progressive and significant (p,0.001) increase in the following MR parameters: wall thickness, postcontrast wall signal intensity, relative contrast enhancement, presence of oedema, ulcers, pseudopolyps and lymph node enlargement. Independent predictors for CDEIS in a segment were wall thickness (p = 0.007), relative contrast enhancement (p = 0.01), presence of oedema (p = 0.02) and presence of ulcers at MR (p = 0.003). There was a significant correlation (r = 0.82, p,0.001) between the CDEIS of the segment and the MR index calculated according to the logistic regression analysis coefficients. The MR index had a high accuracy for the detection of disease activity (area under the receiver operating characteristic (ROC) curve 0.891, sensitivity 0.81, specificity 0.89) and for the detection of ulcerative lesions (area under the ROC curve 0.978, sensitivity 0.95, specificity 0.91) in the colon and terminal ileum.

Aliment Pharmacol Ther 2011; 34: 125–145 Summary Background  Cross‐sectional imaging techniques, including ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI), are increasingly used for evaluation of Crohn’s disease (CD). Aim  To perform an assessment of the diagnostic accuracy of cross‐sectional imaging techniques for diagnosis of CD, evaluation of disease extension and activity and diagnosis of complications, and to provide recommendations for their optimal use. Methods  Relevant publications were identified by literature search and selected based on predefined quality parameters, including a prospective design, sample size and reference standard. A total of 68 publications were chosen. Results  Ultrasonography is an accurate technique for diagnosis of suspected CD and for evaluation of disease activity (sensitivity 0.84, specificity 0.92), is widely available and non‐invasive, but its accuracy is lower for disease proximal to the terminal ileum. MRI has a high diagnostic accuracy for the diagnosis of suspected CD and for evaluation of disease extension and activity (sensitivity 0.93, specificity 0.90), and is less dependent on the examiner and disease location compared with US. CT has a similar accuracy to MRI for assessment of disease extension and activity. The three techniques have a high accuracy for identification of fistulas, abscesses and stenosis (sensitivities and specificities >0.80), although US has false positive results for abscesses. As a result of the lack of radiation, US or MRI should be preferred over CT, particularly in young patients. Conclusions  Cross‐sectional imaging techniques have a high accuracy for evaluation of suspected and established CD, reliably measure disease severity and complications; they may offer the possibility to monitor disease progression.