Magnetic resonance enterography

Panorama general

Magnetic resonance enterography (MR enterography) is a type of magnetic resonance imaging (MRI) that makes detailed pictures of the small intestine. It also is called MRI enterography or small bowel MRI. MR enterography is painless. It can show the bowel wall and tissues around the bowel without using X-rays or other radiation.

A regular abdominal MRI gives a broad view of abdominal organs, but MR enterography is more specific. MR enterography uses contrast material that you drink, called oral contrast, and special imaging steps to evaluate the small intestine. The imaging may show nearby structures in the scanned area, but it is not designed to fully evaluate the colon, stomach, pancreas or every other abdominal organ.

Por qué se hace

Your care team may order MR enterography to diagnose or monitor a condition that affects the small intestine. MR enterography often is used for Crohn's disease because it shows the full thickness of the bowel wall and tissues outside the bowel.

MR enterography may show or help evaluate:

• Inflammation. MR enterography may show bowel wall thickening, ulcerations and swelling. It also may show where inflammation is located and how much bowel is affected.
• Narrowing or blockage. MR enterography can show narrowed areas, called strictures, and signs of a blockage, also called a bowel obstruction.
• Fistulas and abscesses. Fistulas are connections that form between the bowel and another structure. Abscesses are pockets of infection.
• Bleeding or blood vessel changes. MR enterography may help find the cause of bleeding or changes in blood vessels in the small bowel.
• A mass or tumor. MR enterography may help find or show more detail about a growth in the small intestine. Other procedures may be needed to learn whether the growth is small intestine cancer. These procedures may include endoscopy to look inside the digestive tract, a biopsy to remove tissue for testing, or surgery.
• Changes over time. MR enterography can help show how well treatment is working and look for disease that returns after bowel surgery.

Conditions that usually need other tests

MR enterography can show bowel changes that may happen with many conditions. But other digestive conditions usually need different tests.

• Celiac disease. Current guidelines focus on blood tests and, for many adults, an upper endoscopy with biopsies of the small bowel. Some adults who meet specific criteria may not need a biopsy. The guidelines do not include MR enterography as a standard test for diagnosing celiac disease.
• Bowel endometriosis. MR enterography may show changes in the scanned area, but it is not the usual test for suspected endometriosis. Current guidelines recommend pelvic ultrasound and, when needed, a pelvic MRI.

How MR enterography compares with other tests

• MR enteroclysis. MR enteroclysis is a related but different MRI examination of the small intestine. With MR enterography, you drink the contrast solution. With MR enteroclysis, contrast is delivered into the small intestine through a tube. MR enteroclysis is more invasive and is used less often.
• Computed tomography (CT) enterography. Both CT enterography and MR enterography use oral contrast to show the small intestine. CT enterography is faster and less affected by movement, but it uses X-rays. MR enterography takes longer and requires you to hold your breath several times, but it does not use radiation. CT enterography usually uses IV contrast that contains iodine. MR enterography may use IV contrast that contains gadolinium.
• Colonoscopy. During a colonoscopy, a healthcare professional can look directly at the lining of the colon and, when needed, the end of the small intestine. The procedure can take tissue samples and remove polyps. MR enterography can evaluate parts of the small bowel beyond the reach of a standard colonoscopy. It also can show the full bowel wall and nearby tissues. The tests often provide different information about the bowel.

Riesgos

MR enterography generally is safe and does not use radiation. The care team screens you before the test and watches you during the scan to lower the risk of problems.

Possible risks and side effects include:

• A reaction to gadolinium contrast. If IV gadolinium is used, reactions similar to an allergy are uncommon and usually mild. Severe reactions are very rare, and the care team is prepared to treat them.
• A kidney-related complication. Nephrogenic systemic fibrosis is a rare but serious condition linked mainly to certain older gadolinium contrast products. Although rare, it can happen in people with severe kidney disease or acute kidney injury, which is a sudden loss of kidney function. The care team may review your kidney health or order a blood test before giving contrast.
• Effects from glucagon or another medicine. You may receive glucagon or another medicine to briefly slow bowel movement and make the images clearer. Glucagon can cause nausea, vomiting, feeling faint or low blood sugar later. The care team reviews your health history before giving it.
• Risks from metal or implanted devices. The MRI magnet used in MR enterography can move some metal objects or affect an implanted device that is not safe for MRI. Metal also can interfere with the images, so careful screening is important.
• Risks from sedation or anesthesia. If medicine is used to help you relax or sleep, the care team watches you. Sedation may be considered for some children or for people who cannot stay still for the scan.

Tell your care team if you are or might be pregnant. MRI scanning without contrast may be used during pregnancy when medically needed. Gadolinium usually is avoided during pregnancy unless the expected benefit is greater than the possible risk.

Cómo prepararte

Follow the instructions from the imaging center. Preparation varies by location, age and the reason for the test. The instructions you receive take priority over this general information.

Many adult MR enterography preparation instructions ask you not to eat for 4 to 6 hours before the test. Current guidance for inflammatory bowel disease describes drinking about 1 liter (about 34 fluid ounces) of contrast that contains mannitol or polyethylene glycol about 45 minutes before the scan. The product, amount and timing vary. Drinking more than 1 liter has not been shown to improve how well the bowel expands.

Before the appointment, tell your care team about:

• Medicines and supplements. Ask whether to take your usual medicines on the day of the test.
• Your health history. Tell the care team about kidney disease, diabetes, recent surgery, allergies, and any previous reaction to contrast or glucagon.
• Pregnancy or possible pregnancy. Tell the care team before the test.
• Metal or implanted devices. Tell the care team about a pacemaker, implant, metal fragment, surgical clip, medicine patch, body piercing or other metal in or on your body.
• Fear of enclosed spaces, also called claustrophobia, or difficulty lying still. Ask about ways to make the test more comfortable or about medicine before the appointment. Arrange for someone to drive you home if you receive a sedative.

Wear comfortable clothing without metal, or plan to change into a gown. Leave jewelry and valuables at home if possible. Oral contrast may cause diarrhea, so plan for possible restroom stops on the way home, and find a restroom before leaving the imaging center.

Qué esperar

The MRI scan often takes 30 to 45 minutes. Drinking oral contrast often begins about 45 minutes before the scan. Check-in, safety screening, changing clothes and placing an IV take more time. The full visit usually lasts longer than one hour. Ask the imaging center how long the full visit is expected to take.

Before the procedure

A technologist reviews MRI scan safety questions with you and explains the test. You may change into a gown and store metal objects outside the scanner room.

You drink the oral contrast in portions over the time set by the care team. The contrast separates and expands sections of the small bowel so the bowel wall shows more clearly on the images.

• An IV may be placed in your arm or hand to give contrast or medicine.
• Some MR enterography tests use IV gadolinium, but others do not.
• Whether you receive IV gadolinium depends on the reason for the test, the imaging center's protocol and your health history.

The general MRI steps are similar for children. Some imaging centers have staff who help children prepare by explaining the scanner and the sounds it makes. Sedation or anesthesia may be considered when a child cannot stay still. The imaging center gives instructions for fasting, oral contrast and medicines. The amount of oral contrast and some medicines may vary based on the child's age.

During the procedure

The MRI scanner used in MR enterography is a large cylinder with a tunnel through the center and openings at both ends. You lie on a padded table that moves into the scanner. A device called a coil may be placed over your stomach area to help make the images.

The scanner makes loud tapping, knocking and humming sounds.

• You receive earplugs or headphones.
• The technologist works in a nearby room and can see, hear and speak with you.
• You may receive a call button or squeeze ball to alert the technologist if needed.

Lie still during the scan. You may be asked to hold your breath several times. Tell the technologist if you have pain, feel unwell or need help. Movement can blur the images, so part of the scan may need to be repeated.

You may receive glucagon or another medicine to briefly slow bowel movement and make the images clearer. A common adult dose for MR enterography is 0.5 to 1 milligram of glucagon through an IV. The medicine, how it is given, the dose and the timing vary based on the imaging center's protocol and your needs.

If your test includes IV gadolinium, the technologist gives it during the scan and then takes more images.

After the procedure

If you did not have sedation, you usually can return to your usual activities and diet after the procedure. Follow any instructions from your care team that may be different.

Oral contrast may cause temporary loose stools or diarrhea, cramping, bloating, nausea or vomiting.

If you had sedation, you need time to recover and someone to drive you home. Seek emergency care for trouble breathing, swelling of the face or throat, fainting, or other signs of a serious reaction after IV contrast or medicine.

Practical tip: Oral contrast may cause diarrhea. Ask where the nearest restroom is, and plan for possible restroom stops on the way home.

Resultados

A doctor specially trained to interpret MRI scans, called a radiologist, looks over the images and reports the findings to the healthcare professional who ordered the test. Ask when and how you will get the results.

The report may say whether the scan shows inflammation, thickening of the bowel wall, a narrowed area, a blockage, a fistula, an abscess, bleeding or a mass.

• The report may describe where the affected area is, how long it is and how severe the changes are. It also may say whether nearby tissues are involved.
• Images may be less clear if there is not enough contrast in the bowel, the bowel does not fill well, or movement or breathing affects the scan.
• MR enterography does not replace all blood tests, biopsies or endoscopic exams.

Your next steps depend on why the test was ordered and what the report shows. You may need blood or stool tests, a colonoscopy or another endoscopic test, a biopsy, more imaging tests, a change in your medicine, or a visit with a surgeon.

Estudios clínicos

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