Medical research and diagnostics

Magnetic resonance imaging (MRI) of the intestine

Intestinal magnetic resonance imaging is a visual test that gives detailed pictures of the intestine. This method can help your doctor diagnose inflammation, bleeding, obstruction, and other problems. It is non-invasive and does not use ionizing radiation. MRI uses a magnetic field to create detailed images of the intestines. Computer analyzes the image. Before the exam, oral and intravenous contrast material is administered to highlight the intestines. You can also inject a medication to reduce bowel movement (peristalsis), which may interfere with imaging. It is very important to inform the doctor about any health problems, recent surgeries or allergies and whether there is a possibility that the patient is pregnant. The magnetic field is not harmful, but may cause malfunction of some medical devices. Most orthopedic implants pose no risk, but you should always tell the technologist if there are any devices or metal in the body.

What does the equipment look like

Usually, a magnetic resonance imaging scanner consists of a large cylindrical tube surrounded by a circular magnet. The patient lies on a movable examination table, which slides into the center of the magnet. Some newer MRI machines have a larger opening, which may be more convenient for larger patients or patients with claustrophobia.

Other MRI machines are open on the sides (open MRI). Some magnetic resonance scanners, called short-circuited systems, are designed so that the magnet does not completely surround the person. The open ones are especially useful for studying larger patients or patients with claustrophobia. Newer open MRI units provide very high-quality images for many types of studies. Older open MRI devices may not provide the same image quality. Some types of studies cannot be performed using an open MRI. A computer workstation processing image information is located in a separate room.

How does this procedure happen

Unlike conventional X-ray studies and CT, during MRI studies, ionizing radiation is not used. Instead, the RF pulses reconfigure the hydrogen atoms that naturally exist inside the body when the patient is in the scanner, without causing any chemical changes in the tissues. As the hydrogen atoms return to their normal alignment, they release different amounts of energy, which vary depending on the type of body tissue from which they come. An MRI scanner captures this energy and creates a picture of tissues scanned based on this information. Electric current is not in contact with the patient. Then the computer processes the signals and generates a series of images, each of which shows a thin section of the intestine. The images can then be studied from different angles by an interpretive radiologist. Often, abnormal (diseased) tissue differentiation from normal tissues is better with MRI than with other imaging techniques, such as X-rays, CT, and ultrasound.

Bowel MRI

Doctors use MRI scans to determine the presence and location of such intestinal diseases:

  • the presence and complications of Crohn's disease, and other inflammatory bowel diseases;
  • inflammation;
  • sources of bleeding and vascular anomalies;
  • tumors;
  • abscesses and fistulas;
  • intestinal obstruction.

How to prepare

Medicines and food can be taken as usual. Some MRI scans may require the use of a contrast agent. A radiologist, technologist or nurse should ask whether a patient is allergic of any kind, for example, is allergic to iodine or radiopaque material, drugs, food or the environment, or is there asthma. The contrast material most commonly used for MRI research contains a metal called gadolinium. Gadolinium can be used in patients who are allergic to iodine contrast. Much more rarely, the patient is allergic to a gadolinium based contrast agent used for MRI than to iodine-containing contrast for CT. However, even if the patient is known to be allergic to gadolinium contrast, it can still be used after appropriate prior treatment. You also need to tell the radiologist if there are any serious health problems or any recent surgery. Some conditions, such as severe kidney disease, may interfere with the use of gadolinium contrast for MRI. If there is a history of kidney disease or liver transplantation, a blood test will be necessary to determine if the kidneys are functioning adequately.

Jewelry and other accessories should be left at home, if possible, or removed before an MRI scan. Since they can affect the magnetic field, metal and electronic subjects are not allowed into the exam room. In addition to affecting MRI images, these objects can cause damage.

These items include:

  • watches, hearing aids;
  • metal zips and studs;
  • removable dentures;
  • glasses, pens, pocket knives;
  • piercings.

In most cases, the MRI test is safe for patients who have metal implants, except for some species. People with these implants cannot undergo this study, and they are prohibited from entering the area where MRI scans are occurring:

  • cochlear (ear) implant;
  • some types of clamps used for brain aneurysms;
  • almost all cardiac defibrillators and pacemakers.

It is necessary to inform the doctor if there are medical or electronic devices in the body. These items may interfere with the study or potentially pose a risk depending on their nature and the strength of the MRI magnet. Some implanted devices may take time after placement, before being safe for an MRI, usually it takes no more than six weeks. Examples include, but are not limited to: artificial heart valves, implanted medicinal infusion holes, artificial limbs or metal joint prostheses, implanted nerve stimulants, pins, screws, plates, stents. If there is any question about their presence, X-ray diagnostics can be used to detect and identify the localization of any metal objects. The magnetic field does not affect tooth fillings and braces. Family members accompanying patients to the scanning room should also remove metal objects and inform the doctor about any medical or electronic devices they may have.

MRI intestine for pregnant women

Women should always inform their physician or technologist if there is a possibility that they are pregnant. MRI has been used to scan patients since the 1980s without reporting any negative effects on pregnant women or their unborn children. However, since the unborn baby will be in a strong magnetic field, pregnant women should not pass this exam during the first three to four months of pregnancy, if it is assumed that the potential benefits of MRI do not outweigh the potential risks. Pregnant women should not take injections of gadolinium contrast media, unless it is absolutely indicated for treatment.

MRI for children

Infants and young children usually require sedation, or anesthesia, to complete the MRI test without movement. Regardless of whether the child requires sedation, the choice of sedation depends on the child’s age, intellectual development, and type of study. Moderate and conscious sedation can be provided on many sites. A doctor specializing in sedation or anesthesia for children must be present during the study for the safety of the child.

How is the procedure performed

Before the procedure, the patient needs to drink several glasses of an aqueous solution mixed with a contrasting material. Straps and rollers can be used to help the patient stay in place and maintain the correct position during imaging. Devices that contain coils capable of transmitting and receiving radio waves can be placed around or near the area of ​​the body under study. The patient will be placed in an MRI magnet, and the radiologist will conduct an examination while working at the computer outside the room.

What are the benefits and risks?

Advantages of intestinal MRI:

  1. MRI is a non-invasive imaging method that is not associated with ionizing radiation.
  2. MRI can detect abnormalities that may be obscured by bone and not visible during other imaging techniques.
  3. Contrast material used in MRI is less likely to cause an allergic reaction than during use of iodine-based contrast materials, which are used for routine X-ray studies and CT scans.
  4. MRI of the intestines helps identify areas of inflammation of the intestines due to diseases such as Crohn's disease.
  5. Because intestinal MRI does not include ionizing radiation, the procedure may be preferable to assessing young patients with inflammatory bowel disease who may undergo multiple exams throughout their lives.
  6. MRI of the intestine can eliminate the need for invasive endoscopy.

Method risks:

  1. An MRI scan is practically not at risk for the patient if the relevant safety rules are observed.
  2. When using sedation, there is a risk of excessive sedation. However, the technologist or nurse will monitor vital signs to minimize this risk.
  3. Although the magnetic field itself is not harmful, implanted medical devices containing metal can cause failures or cause problems during an MRI.
  4. Nephrogenic systemic fibrosis is a recognized but rare complication of MRI, which is believed to be caused by the administration of high doses of gadolinium-based contrast material in patients with very poor kidney function. A careful assessment of kidney function before considering a contrast injection minimizes the risk of this very rare complication.
  5. There is a slight risk of allergic reactions if contrast material is injected. Such reactions are usually mild and easily controlled drugs.

What are the limitations of intestinal MRI

High-quality images are guaranteed only if the patient can remain stationary and follow the instructions for holding the breath during image recording. If the patient is anxious, confused, or has felt severe pain, it may be difficult for him to lie still while imaging.
A person with a large weight may not fit into the parameters of certain types of MRI devices.
The presence of an implant or other metal object sometimes makes it difficult to obtain clear images due to the appearance of bar-shaped artifacts from metal objects. Movement of the patient can have the same effect.
Although there is no reason to believe that magnetic resonance imaging is harmful to the fetus, pregnant women are usually advised not to have an MRI exam during the first trimester, unless medical intervention is required.
For optimal results, the patient should consume the entire dose of oral contrast agent, remain stationary and follow the instructions for breathing. Moreover, the results can be compromised if the patient cannot receive intravenous contrast material (gadolinium).
An MRI of the intestine takes longer (30 to 45 minutes) than a CT scan (two to four minutes).

MRI or colonoscopy

MRI of the intestines has both its advantages and disadvantages, which are also observed during colonoscopy. However, unlike colonoscopy, this screening method does not require the introduction of a long tube into the rectum, that is, this research method is more tolerant. In addition, with the use of a special technique, patients do not need to undergo the inconvenient bowel cleansing required by conventional colonoscopy.

New data show that MRI of the intestine can accurately detect polyps that can become malignant. However, for more accurate detection of small polyps, improvements to this technique are needed. These results were obtained from a study of 315 adults over the age of 50 who underwent MRI colonoscopy screening. Two days before screening, the subjects drank a liquid that “marked” any stool into the intestine, which made it easier for doctors to search for polyps. No bowel cleansers were given, although rectal water enema was used during visualization to expand the bowel. There were no sedatives or painkillers. The findings on MRI colonography were compared with results obtained with traditional colonoscopy. The researchers found that MRI colonography is pretty good at detecting polyps with a diameter of more than 5 millimeters. In contrast, MRI colonography almost always missed smaller polyps. Although the results are encouraging, researchers believe that traditional colonoscopy will remain the first screening method for the treatment of colon cancer. An important advantage of traditional colonoscopy is the detection of polyps that can be removed or biopsied during the procedure.

Watch the video: What to Expect: Magnetic Resonance Enterography MRE Scans (January 2020).