MRE (Magnetic Resonance Enterography) is a specialized, non-invasive imaging test that uses MRI technology to visualize the small bowel (small intestine). This procedure utilizes a strong magnetic field and radio waves to generate highly detailed cross-sectional images of the gastrointestinal tract and surrounding tissues. Unlike standard X-rays or CT scans, MRE does not use ionizing radiation, making it a preferred option for patients who require repeated imaging over time. The goal of MRE is to achieve optimal distention of the small intestine to allow for a clear view of the bowel wall and lumen.
Why Doctors Order MRE
Doctors frequently order MRE to assess conditions affecting the small bowel, an area often difficult to examine fully with traditional endoscopy or colonoscopy. The superior soft tissue contrast resolution offered by MRE makes it highly effective for identifying subtle changes within the intestinal wall. It is particularly useful in the diagnosis and long-term monitoring of Inflammatory Bowel Diseases (IBD), most notably Crohn’s disease, which commonly affects the small intestine in about 70% of patients.
The technology allows physicians to visualize the extent and severity of inflammation in the bowel wall, differentiating between active disease and chronic damage. Active inflammation is often characterized by significant bowel wall thickening, which is considered abnormal when it exceeds three millimeters in a distended segment. MRE detects complications related to IBD, such as strictures (areas of narrowing) and fistulas (abnormal connections between the bowel and other organs or the skin). MRE can also investigate unexplained gastrointestinal bleeding, persistent abdominal pain, or small bowel tumors, providing a comprehensive assessment of the intestinal lumen and surrounding abdominal structures.
Preparing for the Examination
Patient preparation is necessary for a successful MRE, requiring the small bowel to be adequately filled with fluid for clear imaging. Patients are required to fast from solid food for four to six hours prior to the procedure to clear the stomach and upper digestive tract. This fasting period minimizes motion artifacts from digestion and helps ensure that food residue does not obscure potential lesions.
The most distinctive preparation step involves drinking a large volume of oral contrast agent immediately before the scan, typically around 1.5 to 2 liters of fluid. This contrast, often a biphasic solution like a polyethylene glycol (PEG) or mannitol-based mixture, is designed to travel through the small intestine, distending the loops of bowel. The patient is instructed to consume this liquid gradually over a period of 45 to 60 minutes in the clinic, allowing the contrast to reach the terminal ileum, the most common site of Crohn’s disease involvement. Patients must also notify staff about any pre-existing conditions, particularly kidney issues, as these may impact the safe administration of the intravenous contrast used later in the procedure.
The MRE Procedure Step by Step
The physical process begins once the oral contrast has distributed throughout the small bowel, which may be confirmed with a preliminary scan sequence. The patient is positioned on the MRI table, lying flat on their back, and special coils are placed over the abdomen and pelvis to acquire the imaging signal. An intravenous (IV) line is placed in the arm to allow for the injection of two different medications during the scan.
The first injection is often a smooth muscle relaxant, such as glucagon or hyoscine butylbromide, administered shortly before the main imaging sequences begin. This medicine temporarily slows down the natural, involuntary movement of the bowel, known as peristalsis, which helps prevent motion-related blurring of the images. Following this, a second IV injection of a Gadolinium-based contrast agent is given, which circulates through the bloodstream and enhances the visibility of blood vessels and inflamed tissue.
The patient is then moved into the bore of the MRI scanner, which resembles a large, open-ended tunnel. The entire scan usually lasts between 30 and 45 minutes, during which time the machine produces loud knocking and thumping sounds, necessitating the use of headphones or earplugs. Throughout the acquisition of the images, the technologist will communicate with the patient and ask them to hold their breath briefly, often for up to 20 seconds, to minimize breathing-related movement.
Interpreting the Scan Results
Once the procedure is complete, the acquired images are sent to a specialized radiologist for detailed analysis. The radiologist carefully evaluates the entire small bowel, looking for specific imaging features that indicate disease activity or complication. A primary focus is on the degree of bowel wall thickening and the pattern of enhancement after the injection of the Gadolinium contrast.
Active inflammation typically causes the bowel wall to appear brighter on T2-weighted images due to edema, and it shows a high degree of enhancement on T1-weighted images, reflecting increased blood flow and permeability. Conversely, chronic damage, such as a fibrotic stricture, may display less enhancement and a lower signal intensity on T2-weighted images. The radiologist also searches for signs of penetrating disease, such as abscesses (collections of pus) or fistulas, which appear as thin tracts of contrast extending outside the bowel wall. The final report, detailing the extent and nature of any findings, is then transmitted to the referring physician who will discuss the results and the appropriate follow-up care with the patient.