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Objective:
Diffusion-weighted MRI (DWI) is increasingly utilized in the body for lesion characterization and assessing treatment response. The intravoxel incoherent motion (IVIM) approach in DWI has been proposed to enable quantitative parameters that separately reflect water diffusivity (D), tissue perfusion (D*), and perfusion fraction (f), therefore accounting for the effects of micro-capillary perfusion on DWI. In patients with Crohn’s disease, significant differences in IVIM parameters have been reported between normal and inflamed bowel segments. We sought to determine if IVIM measures from the terminal ileum change over time in response to medical treatment (anti-TNF-alpha), correlate these measures with clinical markers of inflammation, and compare IVIM measures of the bowel wall in healthy versus Crohn's patients.

Materials and Methods:
In this prospective study, 20 children and young adults with newly diagnosed ileal Crohn’s disease and 15 healthy controls underwent investigational MRI examinations of the small bowel between 12/2018 and 10/2021. Participants with Crohn's underwent investigational MRI at baseline as well as 6 weeks, and 6 months following initiation of anti-TNF-alpha therapy. To acquire quantitative IVIM measures (D, D*, f), we averaged the results from two ROIs (from two separate images) placed on axial DWI images showing the most inflamed portion of the ileum (9 b-values, ranging from 0 to b=800 s/mm2). A mixed-effects model approach was utilized to assess for changes in IVIM parameters over time. Spearman correlation was used to evaluate associations between IVIM measures and laboratory markers of intestinal inflammation. Unpaired T-tests were used to compare IVIM between Cronh's participants and controls at baseline.

Results:
The median patient age for participants with Crohn’s disease was 14 years (12 male) and 17 years for healthy controls (8 female). Mean IVIM f values increased over time in response to medical therapy (mean f at baseline, 0.21 ± 0.05; 6 weeks, 0.25 ±0.07; 6 months 0.29 ± 0.10; p=0.016). Mean IVIM D* values increased over time in response to medical therapy (mean D* at baseline, 10.86 ± 3.02; 6 weeks, 11.75 ± 2.82; 6 months 13.26 ± 3.265; p=0.047). Mean IVIM D values did not significantly differ temporally with treatment (p=0.108). Patient erythrocyte sedimentation rate showed a moderate negative correlation with mean IVIM f (r= -0.49, p<0.001), D (r= -0.40, p=0.002), and D* (r= -0.31, p=0.02). Patient albumin showed a moderate positive correlation with mean IVIM f (r =0.45, p<0.001), D (r = 0.37, p=0.005), and D* (r = 0.29, p=0.035). Mean IVIM D (p<0.001), D* (p=0.004), and f (p=0.001) values were higher for participants with Crohn’s versus healthy controls.

Conclusion:
In children and young adults with newly diagnosed ileal Crohn’s disease, IVIM perfusion fraction (f) and tissue perfusion (D*) increased over time in response to biological treatment. There was a moderate correlation between IVIM measurements and certain clinical inflammatory markers. IVIM measures were significantly higher in healthy controls compared to Crohn's patients.