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Objective:
Given the significant difference in treatment, strictures that are predominantly fibrotic are important to distinguish from predominantly inflammatory strictures in Crohn's disease (1). Fibrotic and inflammatory strictures in Crohn’s disease can be difficult to differentiate on single or biphasic CT enterography (2). MRI provides additional value for characterization of fibrotic strictures (3,4), however can be limited due to resource availability. In this study, we added a 7 minutes delayed post contrast phase in the low dose CT enterography (LD-CTE) protocol, and aim to compare its performance to MR enterography (MRE), for characterization of intestinal fibrosis and inflammation.

Materials and Methods:
Twenty-four adult patients with histopathological proven Crohn’s disease (CD) and fibrotic strictures were prospectively recruited. LD-CTE with a delayed 7 minutes post contrast acquisition and MRE were performed within 3 months of initial diagnosis. Three gastrointestinal (GI) radiologists with 5 to 8 years of experience independently evaluated both CTE and MRE for the presence of delayed enhancement at 7 min (DE), progression of enhancement (PE) from 50s to 7 min and quantitative percentage of enhancement gain (based on average of 3 ROIs) from 50s to 7 min. Inflammatory markers including ulcerations, blurred margins, comb sign and enlarged lymph nodes were also assessed. Consensus reads from the 3 readers on LD-CTE was compared to consensus reads from MRE, and inter-observer agreement was assessed using kappa value.

Results:
LD-CTE with delayed requisition demonstrated excellent concordance with MRI for delayed enhancement (DE) and progression of enhancement (PE) (91.3%, and 90.9%, respectively). There was no significant difference in percentage of enhancement gain from 50 s to 7 min between CTE and MRE (p value = 0.11). Inter-reader agreement for DE was substantial (kappa=0.65) and moderate (kappa=0.59) for PE. Diagnostic accuracy of CTE compared to MRE for ulceration, blurred margin, comb sign and enlarged lymph nodes was 77.3%, 100%, 95.2%, 95.4% respectively. Mean and median effective dose of the 7 minutes delayed phase were 1.4 and 1.1 mSv respectively.

Conclusion:
In this pilot cohort, LD-CTE with 7 minutes delayed phase showed comparable performance to MRE, for identification of intestinal fibrosis and inflammation in Crohn's disease. The addition of a 7 minutes delayed phase had very little added radiation dose , and LD-CTE with 7 minutes delayed acquisition have the potential to be an alternative to MRE for the assessment of intestinal fibrosis in CD. If validated in larger cohort, these results will add clinical value particularly in institutions with limited MRI access.