Background and purpose: magnetic resonance enterography has been increasingly used for the diagnosis and follow-up of Crohn's disease (CD). The purpose of the study was to compare the apparent diffusion coefficient (ADC) with wall enhancement for the differentiation of severe, moderate or no inflammation activity in the ileum.
Methods: a prospective, blinded study was conducted of 46 CD patients with a clinical Crohn's disease activity index (CDAI) ≥ 220 and a simple endoscopic score for Crohn's disease (ES-CD) ≥ 7, which yielded 58 inflamed segments with CD. Twenty controls were also included. All segments were characterized by four ADC readings. The two different enhancement patterns observed in inflamed segments, transmural or mucosal, were associated with severely (23) or moderately (35) active CD.
Results: the ADC value decreased from 2.79 ± 0.35 x 10-3 mm2/s for normal segments to 1.81 ± 0.39 x 10-3 mm2/s for the moderately inflamed segments and 1.15 ± 0.20 x 10-3 mm2/s for severely inflamed segments (p ≤ 0.0001). ROC curve analysis on the basis of the three ADC distributions showed a very good discrimination capability with an area under the curve of 0.95. Three groups were defined as follows: normal ileum ADC > 2.4 x 10-3 mm2/s, moderate stages of inflammation 1.5 x 10-3 mm2/s < ADC ≤ 2.4 x 10-3 mm2/s and severe stages of ADC ≤ 1.5 x 10-3 mm2/s.
Conclusions: the ADC value reliably discriminates between normal and inflamed ileum and also distinguishes between severe and moderate inflammation.