Contemporary Imaging Assessment of Strictures and Fibrosis in Crohn Disease, With Focus on Quantitative Biomarkers: From the AJR Special Series on Imaging of Fibrosis.

Patients with Crohn disease commonly have bowel strictures develop, which exhibit varying degrees of inflammation and fibrosis. Differentiation of the distinct inflammatory and fibrotic components of strictures is key for the optimization of therapeutic management and for the development of antifibrotic drugs. Cross-sectional imaging techniques, including ultrasound, CT, and MRI, allow evaluation of the full thickness of the bowel wall as well as extramural complications and associated mesenteric abnormalities. Although promising data have been reported for a range of novel imaging biomarkers for detection of fibrosis and quantification of the degree of fibrosis, these biomarkers lack sufficient validation and standardization for clinical use. Additional methods, including PET with emerging radiotracers, artificial intelligence, and radiomics, are also under investigation for stricture characterization. In this review, we highlight the clinical relevance of identifying fibrosis in Crohn disease, review the histopathologic aspects of strictures in Crohn disease, summarize the morphologic imaging findings of strictures, and explore contemporary developments in the use of cross-sectional imaging techniques for detecting and characterizing intestinal strictures, with attention given to emerging quantitative biomarkers.

Untangling and segmenting the small intestine in 3D cine-MRI using deep learning.

Cine-MRI of the abdomen is a non-invasive imaging technique allowing assessment of small intestinal motility. This is valuable for the evaluation of gastrointestinal disorders. While 2D cine-MRI is increasingly used for this purpose in both clinical practice and in research settings, the potential of 3D cine-MRI has been largely underexplored. In the absence of image analysis tools enabling investigation of the intestines as 3D structures, the assessment of motility in 3D cine-images is generally limited to the evaluation of movement in separate 2D slices. Furthermore, while a segmentation map of the small intestine would be required for a number of automatic analysis tasks, deep learning based segmentation of the small intestine generally performs poorly due to the large variety in shapes, sizes and locations in the abdomen among different patients. Using a data set of 3D cine-MRI scans from 14 healthy volunteers, we developed a multi-task method that automatically tracks individual segments of the small intestine in a time-point from 3D cine-MRI scans, using a stochastic tracker built on top of a CNN-based orientation classifier. The method additionally performs segmentation, conditioned on the locations of intestinal centerlines. We demonstrate the benefit of our stochastic tracking strategy and we show that our proposed segmentation method performs significantly better than an identical network without centerline conditioning. Furthermore, we assess the robustness of the method through evaluation on a set of patients with severe bowel disease. In terms of centerline tracking, our method achieves a recall of 0.74±0.07, a precision of 0.80±0.06 and an F1 score of 0.77±0.05 in the set of healthy volunteers. In the set of patients, it achieves a recall of 0.76±0.12, a precision of 0.86±0.11 and an F1 score of 0.80±0.08. Segmentation achieves a Dice coefficient of 0.88±0.03 in the set of healthy volunteers and 0.79±0.09 in the set of patients. By extracting a structural representation of the small intestine, the presented method provides a major first step towards automatic detailed quantitative assessment of small intestinal motility in abdominal 3D cine-MRI.

Definition of large bowel obstruction by primary colorectal cancer: A systematic review.

AIM: Controversies on therapeutic strategy for large bowel obstruction by primary colorectal cancer mainly concern acute conditions, being essentially different from subacute obstruction. Clearly defining acute obstruction is important for design and interpretation of studies as well as for guidelines and daily practice. This systematic review aimed to evaluate definitions of obstruction by colorectal cancer in prospective studies. METHOD: A systematic search was performed in PubMed, Embase and the Cochrane Library. Eligibility criteria included randomized or prospective observational design, publication between 2000 and 2019, and the inclusion of patients with an obstruction caused by colorectal cancer. Provided definitions of obstruction were extracted with assessment of common elements. RESULTS: A total of 16 randomized controlled trials (RCTs) and 99 prospective observational studies were included. Obstruction was specified as acute in 28 studies, complete/emergency in five, (sub)acute or similar terms in four and unspecified in 78. Five of 16 RCTs (31%) and 37 of 99 cohort studies (37%) provided a definition. The definitions included any combination of clinical symptoms, physical signs, endoscopic features and radiological imaging findings in 25 studies. The definition was only based on clinical symptoms in 11 and radiological imaging in six studies. Definitions included a radiological component in 100% of evaluable RCTs (5/5) vs. 54% of prospective observational studies (20/37, P = 0.07). CONCLUSION: In this systematic review, the majority of prospective studies did not define obstruction by colorectal cancer and its urgency, whereas provided definitions varied hugely. Radiological confirmation seems to be an essential component in defining acute obstruction.