Inflammatory bowel disease (IBD) is a common disease affecting over 1.4 million Americans. IBD is generally further classified into one of two distinct pathologic entities: Crohn's disease and ulcerative colitis \[1\]. Inflammation spanning the wall of the bowel in Crohn's disease predisposes to intestinal stricture formation, which can lead to significant morbidity. Strictures in Crohn's disease are generally classified as inflammatory, fibrotic, or mixed. Differentiation between these categories has important clinical ramifications, as medical therapy is the preferred initial treatment for strictures with an inflammatory component, whereas fibrotic strictures frequently require endoscopic dilatation or surgical resection \[3\].

PET/MR imaging is a relatively novel imaging technique which has distinct potential advantages over conventional cross-sectional imaging (CT/MRI alone) and PET/CT imaging.The full potential of PET/MRI as an imaging modality remains largely untapped, in part due to limitation imposed by cost and time constraints of the exam. Recent advances in MR sequence technology, which allow for shorter scan times, and increased availability of combined PET/MR scanners will likely lead to an increased use of the modality in the future. The radiotracer to be used in this study is Gallium-68 labeled collagen binding probe 8 (\[68Ga\]CBP8), a synthetic collagen-binding probe that has already been investigated at the MGH in patients affected by pulmonary fibrosis. \[68Ga\]CBP8 selectively binds to collagen type I, the predominant extracellular protein in fibrosis. The deposition of type 1 collagen in the extracellular space is the final common pathway of chronic inflammation leading to irreversible end-organ architectural distortion, seen in various diseases states. There are several reasons why the improvement of current PET/MR capabilities would be beneficial. The most direct implication is that improved sensitivity and accuracy of preoperative evaluation of strictures could obviate the need for bowel resection in some cases. The immediate benefit would be avoiding the morbidity/mortality associated with a major abdominal surgery, and, in the long term, possibly avoiding or delaying dreaded complications such as short gut syndrome. Other secondary benefits are more difficult to tangibly quantify but include: 1) Reduced healthcare expenditure by avoiding use of novel biologic agents in such cases that they are unlikely to be beneficial and 2) Improved future research on therapeutic agents in Crohn's disease provided by earlier and more accurate detection of treatment response/non-response.

Twenty-five (25) subjects with Crohn's disease scheduled for possible surgical intervention will be recruited for this study. All subjects recruited for the study will be able to withdraw from the study at any time. The subjects will be referred by MGH Gastroenterology and the Crohn's and Colitis Center. The treating physician will approach the patient about the study and ask if he/she would be willing to be contacted by a member of the study staff. A study staff member will contact the recruited patients, either in person or over the phone. During the initial discussion, the investigator will explain the study in detail to the potential subject and assess inclusion/exclusion criteria. If a potential subject remains interested and meets eligibility criteria, then an appointment will be made for the subject to come to the Martinos Imaging Center in the Charlestown Navy Yard to provide informed consent and participate in the study.

All subjects will undergo placement of an intravenous catheter (IV). Through the same catheter, 10 mL of venous blood will be collected to evaluate blood markers for fibrostenosis. Study subjects will receive an injection of \[68Ga\]CBP8 followed by whole body MR-PET imaging acquired at 1 hour. The PET/MR scan using the collagen-binding radiotracer will be performed at the Martinos Center using the Siemens 3 Tesla Biograph mMR scanner. Standard of care MR enterography sequences will also be obtained to ensure that the subject gets at least the same quality of study and clinical information they would otherwise obtain as part of their routine pre-operative imaging. The images obtained will be interpreted by radiologists at MGH and a report will be made available in the patient's medical record. The imaging findings will be compared to operative findings and postoperative histological findings (when available). If, as part of their routine medical care as directed by their treating physician, subjects undergo endoscopic biopsies or surgery that result in pathology samples, leftover tissue, if any, will be sent to the study Sponsor, Takeda. This will only be leftover tissue handled with subjects' written consent by the Department of Pathology and judged by them as excess leftover tissue. This will not increase the time spent during surgery or endoscopy. This will not be tissue obtained for research purposes only. Takeda will use the leftover tissue to quantify the level of fibrosis in the collected tissues using a combination of H\&E and Masson's trichrome stain followed by imaging profiling using spatial transcriptomics and/or multi-color imaging tools, such as CODEX through a CRO. Histopathological data will be used to establish the diagnostic accuracy, sensitivity and specificity of PET/MR using the collagen-binding probe. This will subsequently be compared to data obtained by using PET and MR enterography alone.