This study will explore the potential for a standardized MRI scan after a liquid meal to be used in diagnosis of the rare but debilitating chronic intestinal pseudo-obstruction (CIPO).

People with chronic intestinal pseudo-obstruction (CIPO) have problems digesting their food properly, due to a problem in their gut nerves or muscle. There are not many good tests to assess how a patient's stomach and bowels are working. Finding out more is the first step in developing a standardized clinical test using MRI to provide a faster diagnosis than is currently possible. Magnetic resonance imaging (MRI) scans allow the investigators to see inside the abdomen. Scans are not painful or harmful and are therefore ideal for repeated measurements. By scanning participants both before and after a test drink the investigators can see exactly how their digestion is working.

The investigators are inviting 16 people who are at least 16 years old, 8 who have CIPO and 8 with chronic constipation, so the investigators can compare the images. Participants will come in for one half day of scanning. The investigators will take a total of 8 scans of their abdomens, every half hour. Participants will also fill in symptom questionnaires at every scan, for example if they feel bloated or have any abdominal pain. Each scan will take about 15 minutes and will require short breath holds. Participants will be able to get out of the scanner at any time point if they feel the need to.

Participants will arrive fasted in the morning and will receive a test drink (a milk-based drink used as an oral nutritional supplement) right after the first scan. All participants will be asked to pause some of their usual medication that has a direct influence on digestion for 24h before the scan day and during the ~4h of the study.

The primary outcome is peak small bowel motility, which the investigators hypothesize to be less active in people with CIPO. Other outcomes include gastric volume, small bowel water content and distribution, peak gastric motility, and gastrointestinal symptoms.

Inclusion Criteria:

• Ability to give informed consent
• Sufficient level of English language to understand study information and respond to symptom questionnaires
• CASES: a clinical diagnosis of primary or secondary Chronic Intestinal Pseudo-Obstruction, excluding adhesional obstruction. PICs will be asked to send clinical documentation that the diagnosis has been confirmed on crosssectional imaging.
• CONTROLS: a Chronic constipation disorder diagnosed according to Rome IV criteria for functional constipation, constipation-predominant irritable bowel syndrome or opioid-induced constipation (diagnostic criteria as listed in Lacy et al 2016)

Exclusion Criteria:

• Inability to tolerate 400 ml liquid challenge meal (oral or through established gastrostomy; according to self-assessment)
• Contra-indication to MRI scanning, such as metal implants, pacemaker etc
• Pregnancy declared by candidate (no formal testing)
• Inability to stop short-acting medications likely to alter small bowel motility, such as antiemetics, fast release opioids, laxatives, and anti-diarrhoeals, on the day before the study (24h before baseline scan; i.e. a total of circa 30h) as well as antibiotics for three days before the study. This only applies to long-term antibiotics commonly given for dysbiosis (small intestinal bacterial overgrowth). A short course of antibiotics given for acute infections will not be interrupted but the study day will be delayed until the course is finished. Patches, long acting formulations such as slow release medication or depot injection medication will be allowed to continue
• Inability to omit parenteral nutrition for 12 hours before the fasting MRI scan (~16h total)
• Medical comorbidity that means subject will not be able to undergo multiple scans e.g. severe respiratory disorder limiting time lying flat; severe musculoskeletal disorder limiting mobility
• Previous small bowel resection (excluding ileostomy, insertion of venting tube or percutaneous endoscopic gastrostomy, appendectomy or cholecystectomy). Patients who have had a colectomy for their CIPO will be eligible.
• Other gastrointestinal disorder likely to alter small bowel function e.g. uncontrolled coeliac disease, Crohn's disease. A diagnosis of small intestinal bacterial overgrowth will not be a reason for exclusion. PICs will be asked to supply information on resections and comorbidities for CIPO participants.

Cases will be recruited through Digestive Diseases clinical services across England; Controls will be recruited from the population of Nottingham.

Anonymised IPD may be available for sharing as part of collaborative data pooling but will not automatically be published as open source due to the possibility of identification through meta-data in a rare disease.