Non-Invasive Colonic Imaging Studies in Inflammatory Bowel Disease

Abstract

The global incidence of Inflammatory Bowel Disease (IBD) is rising, with current prevalence of 0.3%. Objective assessment of colonic inflammation is paramount for diagnosis, monitoring, and clinical management. Endoscopy is the gold standard for objective assessment of colonic disease activity in IBD. However, it has limitations; it requires bowel preparation, can be uncomfortable, is invasive and associated with rare but potentially serious risks such as perforation. Non-invasive colonic imaging may have a role in quantifying colonic disease activity. Non-invasive colonic imaging modalities are widely available, well tolerated, require less intensive bowel preparation, and are routinely used to assess small bowel inflammation. However, the utility of these modalities in assessing colonic inflammation is less clear. This thesis work aimed to investigate their utility. Firstly, a systematic literature review was undertaken to appraise the diagnostic accuracy of non-invasive colonic imaging in both Crohn’s disease (CD) and ulcerative colitis (UC). A meta-analysis of the data was also performed using a bivariate model approach separately for each non-invasive colonic imaging modality. The mean sensitivity and specificity for magnetic resonance imaging (MRI) studies was 0.75 and 0.91, respectively, while for bowel ultrasound (US) studies it was 0.82 and 0.90, respectively. The area under the ROC curves (AUC) was 0.88 (95% CI, 0.82 to 0.93) for MRI, and 0.90 (95% CI, 0.75 to 1.00) for US. Both MRI and US showed high diagnostic accuracy in the assessment of colonic disease activity in IBD patients. Secondly, an evaluation of the dependence of a tagging measurement was performed (for assessing chyme mixing) on inter-observer variability in both the ascending colon (AC) and descending colon (DC). The temporal variation and hence reliability of the colonic tagging technique was also investigated by acquiring multiple measurements over time on healthy participants. The MRI tagging technique can provide an assessment of colonic chyme mixing. The inter-observer study data showed high inter-rater agreement. The temporal variation study showed some individual variations with time suggesting multiple measurements may be needed to increase accuracy. A prospective study was then conducted to determine the feasibility of an MRI protocol to visualise and assess diffusion-weighted imaging (DWI) and motility of the colon wall and content in UC patients. The preliminary findings show that this MR protocol, including quantitative DWI, motility scans, and tagging in the colonic segments, is feasible for use in UC patients. Further data is needed to determine whether any of the parameters measured provide sensitivity to disease activity and inflammation.