MR Enterography - Indications, Procedure, Benefits, Disadvantages, and Limitations

Introduction

Diagnosing gastrointestinal disorders, particularly those affecting the small and large intestine (bowel), is challenging considering the anatomic location and lack of easy access. The most commonly used diagnostic tool is endoscopy. Though endoscopy is regarded as the gold standard for diagnosing most bowel diseases, it is not well tolerated by some patients as it is an invasive test. With endoscopy, it is difficult to gain access to the small bowel. Also, it cannot be used in patients with gastric complications such as bowel obstruction and other intra-abdominal complications. Deeper lesions may also be difficult to visualize by endoscopy. Hence, an efficient and noninvasive diagnostic tool was needed to evaluate the bowels. This was achieved using magnetic resonance imaging to get detailed images of the small intestine.

What Is Magnetic Resonance Enterography?

Magnetic resonance enterography, or MR enterography, is a noninvasive diagnostic imaging test used to visualize the small and large intestines, including the colon. It is a highly safe procedure as there is no radiation involved. It is a specialized form of magnetic resonance imaging. This procedure utilizes magnetic fields and radio waves to capture images of the internal organs and tissues of the body. Various small and large bowel conditions, such as unexplained bleeding, inflammation, and tumors, can be efficiently diagnosed using magnetic resonance enterography. Using a contrast medium while imaging may improve visualization, aiding in better images and precise diagnosis.

What Are the Indications of Magnetic Resonance Enterography?

MR enterography is indicated in the following conditions:

• Preferred diagnostic tool in Crohn’s disease and inflammatory bowel diseases.

• Celiac disease.

• Unexplained internal bleeding.

• Inflammation.

• Intestinal abscesses.

• Trauma, injury, or tear in the intestinal wall.

• Strictures or obstruction in the bowel.

• Tumors.

• Fistulas.

What Are the Pre-procedural Instructions?

• Patients should avoid food or drink for four to six hours before the procedure. Regular medicines can be taken with a few sips of water.

• Patients are advised to reach the diagnostic center at least two hours earlier, for they must be administered contrast agents and other preparations.

• Female patients who are pregnant or could be pregnant should inform the doctor, as MRE is not advisable during the first trimester of pregnancy.

• Patients with a previous history of allergy to contrast materials or drugs should notify the doctor before the procedure.

• Patients with renal diseases or on dialysis should also inform the doctor as the contrast agent used is nephrotoxic and can cause further renal damage.

• Claustrophobic patients (those with a fear of enclosed spaces) can inform the doctor so that they can receive a sedative or relaxant before the procedure.

• Patients should wear loose, comfortable clothes and remove any jewelry or other metallic accessories, including belts, wallets, credit cards, removable dentures, body piercings, electronic watches, pens, mobile phones, eyeglasses, or hearing aids, as metals can interfere with the magnetic field in the MRI (magnetic resonance imaging) unit and can cause potential damage.

• Patients with cochlear implants, pacemakers, dental implants, defibrillators, or aneurysm clips should ideally not be scanned without a thorough evaluation.

• Patients with prostate disease and glaucoma should also notify the doctor as a drug (Glucagon) is administered before the procedure to slow the gastric motility, which is contraindicated in glaucoma and prostate disease patients.

• Orthopedic implants are not a contraindication for MR enterography; however, patients with joint replacement are advised to inform the doctor.

• Patients receiving sedatives for the procedure might require assistance returning home.

• Patients are advised to carry their prescription medicines and recent test reports for the procedure.

How Is Magnetic Resonance Enterography Performed?

• Patients are advised to change into a hospital gown. A relaxant or a sedative may be given if required.

• Patients will be asked to drink an oral contrast medium an hour before the procedure. This helps in enhancing the images of the bowels.

• After an hour, the patients will be taken to the procedural room and asked to lie on the examination table. The table is movable and would slide into a tunnel-like machine, the MRI unit.

• Before scanning, an intravenous (I.V) line will be started to administer injectable contrast. This contrast helps visualize the blood vessels within the small intestine. Patients may feel a metallic taste when the contrast is injected.

• Another drug called Glucagon will be administered next to slow down intestinal motility.

• A balloon enema may be administered for colon examination, which the patient must hold until the procedure is complete.

• The imaging coil, which would be in the form of a blanket, is placed over the abdomen.

• The table then slides into the MRI unit.

• Patients are required to remain still, as any slight movement can blur the images. In addition, patients may hear loud thumping noises, which is normal, and may request earplugs.

• Patients may be asked to hold their breaths while capturing the images.

• MR enterography is usually carried out as an outpatient procedure and may require 45 minutes to one hour.

What Are the Instructions After the Procedure?

• Once the procedure is complete, the I.V. (intravenous) line will be removed, and the patient will be assisted to the bathroom to expel the enema.

• Cramping and nausea are common due to the contrast material but would resolve once the contrast material leaves the body.

• Patients are advised to drink plenty of fluids to expel the contrast material.

• MRI examinations are painless and non-invasive; hence patients have no restrictions. They can continue with their routine activity and diet.

What Are the Benefits and Risks of This Procedure?

Benefits:

• Non-invasive and has no risk of radiation.

• Avoid invasive diagnostic procedures like endoscopy.

• Images can be acquired in multiple planes.

• Preferred diagnostic tool for visualizing the soft tissues.

Risks:

• Patients with implanted devices such as pacemakers, aneurysm clips, hearing devices, defibrillators, ear implants, heart, or dental implants must inform the doctor before the procedure, as this metallic implanted device may interfere with the magnetic field.

• Gadolinium-based contrast agents used in MRI examination are potent nephrotoxins and must be carefully used in patients with chronic renal disease or end-stage renal failure.

• Allergic reaction to the contrast material.

What Are the Disadvantages of This Procedure?

• The scanning time is considerably long; hence it is challenging for patients who find it difficult to remain still, such as those with chronic back pain or other spinal problems.

• It is more prone to develop and display motion-related artifacts, such as those arising from breathing.

• Incompatibility with certain implantable devices.

What Are the Limitations of This Procedure?

• This procedure is not indicated in extremely anxious patients or patients in severe pain, as they may struggle to remain still.

• Obese patients, as it might be challenging for them to fit into the narrow opening of the MRI unit.

• It may be challenging to get clear images for patients with irregular heartbeats.

• Gadolinium contrast should be avoided in pregnancy.

Conclusion

Magnetic resonance enterography is a non-invasive and efficient diagnostic tool to visualize bowels. With enhanced functional imaging and the possibility of obtaining the images in multiple planes, MR enterography is far superior to its invasive endoscopic counterpart.