EVALUATION OF CROHN’S DISEASE ACTIVITY BY DIFFUSION WEIGHTED MAGNETIC RESONANCE IMAGING (MRI)

Background and aim:A new application of MRI is the use of MR sequences DWI (Diffusion Weighted Imaging). These are characterized by a high resolution of contrast that allows to differentiate inflamed small bowel by normal bowel. The diffusion of water is the result of Brownian motion. Using the natural sensitivity of MRI to motion, is possible to measure the ADC (Apparent Diffusion Coefficient), a quantitative parameter of this phenomenon. In active Crohn’s Disease (CD) the high viscosity and cellularity of inflamed tissue may reduce the extracellular space, so restricting the diffusion of water. The aims of this study were: to evaluate in patients with CD the diagnostic capability of DWI sequences in the detection of small bowel inflammation with the measurement of ADC and to verify the correlation between findings of DWI sequences (both qualitative and quantitative) and the Harvey-Bradshaw Index (HBI). Material and methods:A retrospective search of our database was performed. We reviewed 14 patients with CD of terminal ileum (TI) who underwent MR enterography (including dynamic contrast enhanced MRI and DWI) between February 2010 and April 2012. Inclusion criteria were: histologic diagnosis of small bowel CD, HBI calculated within 1 month and colonoscopy performed within 2 months of MR examination. Conventional MRI findings of TI were recorded together with a semiquantitative evaluation of signal intensity in DWI sequences using a 3-point scale. Regions of interest were drawn over TI and normal ileum to calculate ADC. Results:Among conventional MR findings, mural thickening and increased enhancement were present in all patients; ADC values differed significantly between actively inflamed TI and normal ileum [(1.19±0.22)×10 -3 mm2 /s versus (3.69±0.42)×10 -3 mm2 /s; P<0.00001]; the presence of a strong correlation between DWI images and HBI was demonstrated (r of Pearson=0.67; p=0.009); we did not find a significant correlation between ADC value of TI and HBI. Conclusions:Our study confirms that DWI sequences are useful in distinguishing bowel segments with active inflammation from normal loops in patients with CD. The inflamed intestinal wall is characterized by restriction of diffusion and the ADC value of the segments with active disease is significantly lower than normal. The partial correlation between DWI sequences and HBI may show the usefulness of DWI-MRI in the evaluation of disease activity in CD.