CT colonography for polyp surveillance & MRI features in Crohn’s disease

PART I In this thesis, surveillance CT colonography was evaluated for patients with 6-9 mm polyps as an alternative to colonoscopy in screening for colorectal cancer with CT colonography. We found a high participation rate and a substantial yield for advanced adenomas at surveillance CT colonography. Importantly, no colorectal cancers or adenomas with high-grade dysplasia were detected, suggesting this strategy is safe. By assessing volumetric growth, we demonstrated that one-third of small polyps progressed during a 3-year surveillance period. These growing polyps were more likely to be advanced adenomas than stable or regressing polyps. We also showed that acceptance for surveillance CT colonography was high and burden was low. However, when considering the overall CT colonography screening strategy including the surveillance yield compared to a colonoscopy strategy, there was a significant lower detection rate for serrated adenomas which could potentially influence the value of CT colonography as screening modality. PART II MRI has proven its use in diagnosing and monitoring Crohn’s disease. Numerous MR features have been identified and multiple scorings systems have been developed for assessing and quantifying the degree of inflammation. We determined that the available scoring systems and their incorporated features were comparable in reproducibility, correlation and diagnostic performance. In addition, we determined which MR features were useful in assessing rectal inflammation on perianal MRI. We showed that in addition to wall thickness and mural fat, four features related to the perimural fat tissue were more helpful than the established luminal features