Crohn's disease (CD) is a chronic inflammatory bowel disease (IBD) that can significantly impair patients' quality of life. Due to its transmural nature (affecting the entire thickness of the intestinal wall), it naturally progresses to intestinal destruction (stenosis, fistula), requiring intestinal resection in approximately half of patients during follow-up. The long-term goal for patients is to maintain a normal life, i.e., without symptoms and without intestinal destruction. To this end, short- and medium-term therapeutic goals have evolved in recent years. Clinical remission is not a sufficient goal, as it has not changed the natural history of the disease. The current goal is to achieve a combination of clinical remission and endoscopic mucosal healing, as this is associated with a reduced risk of adverse outcomes (recurrence of symptoms, hospitalization, intestinal resection).

Transmural healing assessed by MRI is also a promising goal associated with a reduced risk of adverse outcomes (recurrence of symptoms, hospitalization, intestinal resection). Furthermore, it is associated with a lower risk of progression to intestinal destruction, unlike endoscopic remission. In this context, transmural healing could soon become the benchmark in terms of therapeutic objectives for Crohn's disease, particularly in the ileum. Although enteric MRI is better accepted than colonoscopy by patients with Crohn's disease, in the ACCEPT1 study, nearly half of patients (48.6%) reported the need to use an intestinal distension product (PEG, mannitol, etc.) as a significant obstacle to repeating entero-MRI, while more than a third complained of vomiting (33.7%) or severe diarrhea (35.0%) induced by these same products. Being able to do without the use of distension products would significantly improve the acceptability of entero-MRI.

We hypothesize that an enteric MRI without distension would lead to poorer ileal distension but would allow inflammatory activity scores to be assessed on MRI in a manner similar to an examination with distension, and thus would not impact the need for therapeutic intensification.

This is a prospective, multicenter (5 centers), cross-sectional concordance study including adult patients with ileal and/or colonic Crohn's disease requiring MR enterography for reassessment of disease activity. Patients will undergo two MR enterography scans at 2 and 7 days intervals. The first scan will be performed without a distension agent, and the second with intestinal distension (as is standard practice). A gadolinium-based contrast agent will be used in both MR enterography scans. Furthermore, the MRI protocols and sequences will be identical. The images will be anonymized and uploaded to a dedicated platform for centralized review by two expert radiologists (randomly selected) blinded to clinical data. The primary endpoint will be the C-score (a quantitative variable), the concordance of which will be assessed using Lin's coefficient.

Inclusion Criteria:

• Patients with Crohn's disease according to European recommendations (ECCO) ≥ 18 years of age
• With known or suspected ileal ± colonic involvement
• Requiring reassessment of disease inflammatory activity according to the clinician
• Able to give informed consent to participate in the research.
• Affiliation with a Social Security scheme
• Agreeing to undergo two MRIs in the same week

Exclusion Criteria:

• Isolated colonic Crohn's disease
• Resection > 1 m of small intestine
• Severe obstructive symptoms defined according to CDOS (Crohn's disease obstructive symptoms score)
• Uncontrolled intra-abdominal abscess
• Isolated anoperineal lesions
• Prevention of postoperative endoscopic recurrence
• Temporary or permanent stoma
• Total colectomy
• Contraindication to MRI
• Pregnant or breastfeeding women
• Protected adults (under guardianship, trusteeship, family authorization, future protection mandate, with representation relating to the person)