Magnetic resonance enterography (MRE) is a specialized, non-invasive imaging test that offers a detailed view of the small intestine. This procedure is a type of magnetic resonance imaging (MRI) tailored specifically to examine the middle portion of the digestive tract. MRE utilizes a powerful magnetic field and radio waves to create cross-sectional images of the internal organs. This technique provides physicians with high-resolution pictures to help diagnose and monitor conditions affecting the small bowel, without using ionizing radiation like X-rays or CT scans.
What Is MR Enterography?
MRE is fundamentally an MRI scan that focuses on the small bowel, or small intestine, where most nutrient absorption occurs. The technique uses a strong magnetic field and radiofrequency pulses to generate signals that a computer interprets into detailed images. The defining feature that makes it “enterography” is the use of contrast agents to achieve a high degree of visualization of this lengthy organ.
To achieve this detail, a large volume of oral contrast solution is administered before the scan. This specialized liquid is consumed to physically distend the small bowel and improve image clarity. Distension is necessary because the small intestine, when empty, appears collapsed, which can obscure potential disease or abnormalities. The oral contrast fills the lumen, allowing radiologists to clearly see the bowel walls and surrounding tissues.
Why Doctors Request MRE
Physicians request MRE to assess specific conditions within the small intestine with high sensitivity. The test is frequently used to diagnose and monitor inflammatory bowel diseases (IBD), particularly Crohn’s disease. MRE allows doctors to evaluate the extent of inflammation, measure the thickness of the bowel wall, and identify complications like strictures (narrowing) or fistulas (abnormal connections).
MRE offers a significant advantage over traditional X-rays or CT scans because it does not expose patients to ionizing radiation. This makes MRE the preferred option for monitoring younger patients who require repeated imaging. Beyond IBD, MRE is also used to investigate sources of chronic, unexplained gastrointestinal bleeding, abdominal pain, or to detect tumors or blockages within the small bowel.
Preparing for the Scan
Preparing for an MRE begins with specific dietary and fasting requirements. Patients are typically instructed not to eat or drink anything for four to eight hours before the exam, though a small sip of water may be allowed for necessary medications. Patients with diabetes or known kidney issues should discuss their condition with their physician, especially since an intravenous (IV) contrast agent will be used later.
The most distinct preparation step involves drinking the oral contrast solution once the patient arrives at the facility. This contrast, which may be up to 1.5 liters, must be consumed over a specific time period, usually between 45 minutes and 1.5 hours before the scan begins. This large volume ensures the entire small intestine is adequately filled and distended for imaging, as poor distension can lead to less accurate images.
What to Expect During the Procedure
The total time spent at the facility, including the oral contrast drinking period, can range from one and a half to two and a half hours. After preparation, a technologist places an intravenous (IV) line into a vein. This IV line is used to inject a second contrast agent, typically a Gadolinium-based solution, later in the scan to enhance the images of the bowel walls and blood vessels.
The patient lies on a movable table that slides into the large, tube-like MRI machine and must remain completely still throughout the imaging. The scan itself usually lasts between 30 and 45 minutes. The machine produces loud, repetitive knocking sounds, so the patient is provided with earplugs or headphones. A medication to temporarily slow down bowel movement, such as Glucagon, may also be injected via the IV line to prevent motion blur and improve image quality.
Safety Considerations and Follow-Up
MRE is generally considered a safe procedure because it avoids ionizing radiation. However, the strong magnetic field means that people with certain metal implants, such as pacemakers, cochlear implants, or aneurysm clips, may not be able to undergo the scan. Patients are carefully screened for any metal objects or implanted devices before entering the scanning room.
The oral contrast can sometimes cause mild side effects such as nausea, abdominal cramping, or diarrhea. The IV Gadolinium contrast has a very low risk of allergic reaction, typically less than that associated with the iodine-based contrast used in CT scans. The images are reviewed by a radiologist, who sends a detailed report to the referring physician, usually within 24 hours. The physician then discusses the results and the next steps for treatment or monitoring with the patient.