About a small bowel MRI scan
The small bowel (small intestine) is the long, coiled part of the gut between the stomach and the large bowel, where most food is digested and absorbed. Because it is long and folded, it is difficult to examine fully with a camera test. A small bowel MRI uses a strong magnetic field and radio waves, without X-rays, to make detailed pictures of the whole length of the small bowel and the tissues around it.
For the pictures to be clear, the bowel needs to be filled and gently stretched with fluid. There are two ways of doing this:
- MR enterography, the most common method, where you drink a special fluid (such as a mannitol drink) over about an hour before the scan
- MR enteroclysis, where the fluid is given through a thin tube passed through the nose into the small bowel; this fills the bowel more completely and can show small changes in the bowel lining better, but the tube can be uncomfortable
There is limited research comparing the two methods directly, and centres choose based on their own protocols. The scanning centre will confirm which method it uses when your appointment is arranged.
Small bowel MRI is especially useful for Crohn’s disease, because it does not use radiation and so can be repeated over the years to check how the disease and treatment are progressing.
What happens during the scan
After you have drunk the fluid (or had it through a tube), you lie on the scanner bed, usually on your front or back, with a coil over your tummy. A small cannula is placed in your arm. During the scan you will usually be given an injection of Buscopan, a muscle relaxant that slows the natural movement of the bowel so the pictures are not blurred, and often an injection of contrast dye (gadolinium). You will be asked to hold your breath for up to about 20–25 seconds at a time. The scanner is loud, so you will wear ear plugs or headphones. Where contrast is needed, it is charged separately.
What the scan can show
A small bowel MRI can help to look at:
- Crohn’s disease, including where it is, how active the inflammation is and how long the affected segments are
- complications of Crohn’s disease, such as narrowing (strictures), fistulas and abscesses
- how well treatment for Crohn’s disease is working
- other causes of inflammation or narrowing in the small bowel
- small bowel tumours and polyps
- causes of unexplained tummy pain, bleeding or anaemia where the small bowel is suspected
Preparing for your scan
You will usually be asked not to eat for about 4 hours before your appointment. You can normally have small amounts of clear fluids, such as water, and take your usual medicines. You will need to arrive about an hour before your scan time to drink the bowel preparation fluid. The scanning centre will give you exact instructions.
The drink often causes diarrhoea afterwards, which can come on quickly, so plan your journey home with this in mind. Buscopan can cause short-lived blurred vision, a dry mouth or a fast heartbeat, so do not drive until these have worn off. Tell us when booking if you have glaucoma, heart problems, myasthenia gravis or problems passing urine, as these can affect whether Buscopan can be used. Very rarely, Buscopan can cause painful red eyes with blurred vision within 24 hours; if this happens, go to A&E straight away.
You can usually eat, drink and take your normal medicines unless the scanning centre tells you otherwise. Wear loose, comfortable clothing without metal zips or buttons, and leave jewellery at home. You will be asked to remove metal items such as hair clips, hearing aids, coins and keys, and you may be asked to change into a gown.
Before the scan you will complete a safety questionnaire. Tell the team if you have a pacemaker, any metal implant, surgical clips or other device, if you have kidney problems or allergies, or if you are, or might be, pregnant or breastfeeding. If you feel anxious in enclosed spaces, let us know when you book. Some centres can offer a relaxant, and if you take one you will need someone to take you home and must not drive for 24 hours.
Frequently asked questions
What is the difference between enteroclysis and enterography?
Both are MRI scans of the small bowel. In enterography you drink the fluid that fills the bowel; in enteroclysis the fluid is given through a thin tube passed through the nose. Enteroclysis can stretch the bowel more evenly but is less comfortable. The scanning centre will tell you which method it uses.
Will the drink give me diarrhoea?
It often does. The fluid used to fill the bowel can cause diarrhoea for a few hours after the scan. Contact your GP if it continues or you are worried.
Why is MRI used for Crohn’s disease?
MRI shows the whole small bowel, including parts that are hard to reach with a camera, and it can show inflammation, narrowing and complications. Because it does not use radiation, it can be repeated safely to monitor the disease.
Can I drive after the scan?
Not until any blurred vision from the Buscopan injection has completely cleared. Many people prefer to arrange a lift, especially as the drink can cause diarrhoea.
Sources
- University College London Hospitals NHS – Having an MRI of your small bowel
- Radiopaedia – MR enteroclysis
- Dorset County Hospital NHS – MRI Small Bowel leaflet
- NHS – MRI scan
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.