To determine the correlation between intravoxel incoherent motion (IVIM) parameters and both histologic inflammatory and fibrotic grades of Crohn disease (CD) in adults.

Prospectively, 17 patients (77 lesions) with a clinical and pathological diagnosis of CD in the first affiliated hospital of sun yat-sen university from July 2015 to June 2016 underwent MRE 15 days before surgery. All patients underwent T₂WI, IVIM and enhanced MRI and calculated IVIM parameters include diffusion-related coefficient (D), perfusion-related coefficient (D^*) and perfusion-related fraction (f). Histological intestinal inflammation and fibrosis was scored using the surgical histopathology as reference standard and further divided into mild-moderate (score 1 to 2) and severe (score 3 to 4) groups. Intestinal microvessel density (MVD) were also analyzed. Differences in IVIM parameters among different histological inflammation and fibrosis grades were assessed with the Kruskal-Wallis test. The Wilcoxon test was used for assessing differences in f between mild-moderate and severe fibrosis. The bivariate correlations between IVIM parameters and histological inflammation and fibrosis grades were analyzed using partial correlation. The bivariate correlations between IVIM parameters and MVD were analyzed using Spearman rank correlation. The areas under the receiver operating characteristics curves (AUROC) were analyzed to evaluate the efficacy for distinguishing severe from mild-moderate fibrosis.

Of 77 surgical specimens, there were 41 mild-moderate and 36 severe inflammatory bowel segments, along with 22 mild-moderate and 55 severe fibrotic bowel segments. Positive correlation was shown between histologic inflammatory and fibrotic scores (r=0.592, P<0.01). MVD (42.7±39.9)/HP presented weak positive correlation with histologic inflammatory scores (r=0.332, P=0.003) while no correlation with histologic fibrotic scores (r=0.129, P=0.262) was presented. Neither the D nor the D^* values significantly correlated with histologic inflammation or fibrosis (P>0.05) while the f value significantly correlated with both histologic inflammation and fibrosis (P<0.05). Significant correlation was present between the f value and histologic inflammatory and fibrotic scores, respectively (r=-0.280, -0.520; P<0.05). There was significant difference in the f value between mild-moderate and severe fibrosis(Z=-5.255,P<0.01). The AUROC for the f value to distinguish between patients with mild-moderate fibrosis and severe fibrosis were 0.885. Using a threshold fractional perfusion of 0.33, the sensitivity and specificity values were 95.5% and 81.8%, respectively. No correlation between f, D and D^* value with histologic fibrotic scores (r=0.129, P=0.262) was presented.

The f value derived from IVIM could help to evaluate the severity of intestinal inflammation and fibrosis CD in adults.

Crohn disease; Magnetic resonance imaging; Inflammation; Fibrosis