Definition
Abdominal magnetic resonance imaging (MRI) is a noninvasive test that uses powerful magnets and radio waves to create pictures of the inside of the belly area. It does not use radiation (x-rays).
Alternative Names
Nuclear magnetic resonance - abdomen; NMR - abdomen; Magnetic resonance imaging - abdomen; MRI of the abdomen
Why the Test is Performed
An abdominal MRI provides detailed pictures of the belly area from many different views. It is often used to clarify findings from previous x-rays or CT scans.
This test may be used to diagnose or evaluate:
- Abnormal growths and tumors
- Blood flow
- Blood vessels
- Lymph nodes
- How certain organs work
MRI can distinguish tumors from normal tissues and can help the doctor determine the tumor's size, severity, and spread. This is called staging.
MRI is sometimes used to avoid the dangers of angiography, repeated radiation exposure, iodine-related allergic reactions.
How the Test is Performed
You will be asked to lie on a narrow table, which slides into a large tunnel-like tube. The health care provider may inject a dye through one of your veins. This helps certain diseases and organs show up better on the images. Small devices, called coils, may be placed around certain body areas to be studied. They also help produce better images.
Unlike and computed tomographic (CT) scans, MRI does not use radiation. Instead, it uses powerful magnets and radio waves. The magnetic field produced by an MRI forces certain atoms in your body to line up in a certain way. It's similar to how the needle on a compass moves when you hold it near a magnet.
The radio waves are sent toward these atoms and bounce back, and a computer records the signal. Different types of tissues send back different signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.
A technologist will operate the machine from a room next door and watch you during the entire study.
Several sets of images are usually needed. Each one takes about 2-15 minutes. A complete scan may take up to 1 hour. Newer scanners may complete the process in less time.
How to Prepare for the Test
There is usually no preparation needed, unless your doctor says you must clean out your bowels. This is often done using a laxative or enema.
You may be asked to wear a hospital gown.
The strong magnetic fields created during an MRI can interfere with certain implants, particularly cardiac pacemakers. People with cardiac pacemakers can not have an MRI and should not enter the MRI area.
If you have any of the following metallic objects in your body, you should not get an MRI:
- Brain aneurysm clips
- Certain artificial heart valves
- Inner ear (cochlear) implants
- Older vascular stents
- Recently placed artificial joints
You will be asked to sign a consent form that says you do not have any of these items in your body.
Before an MRI, sheet metal workers or any person that may have been exposed to small metal fragments should receive a skull x-ray to check for metal in the eyes.
MRI can easily be performed through clothing. However, because the magnet is very, very strong, certain types of metal can cause significant errors, called artifacts, in the images. Also, certain metallic objects are not allowed into the room.
- Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
- Pins, hairpins, metal zippers, and similar metallic items can distort the images.
- Removable dental work should be taken out just prior to the scan.
The MRI magnet is always turned on. Pens, pocketknives, and eyeglasses may fly across the room if they are too close to the magnet. This can be dangerous, so such items are not allowed into the scanner area.
How the Test Will Feel
An MRI exam causes no pain. Some people may become anxious when inside the scanner. If you have difficulty lying still or are very anxious, you may be given a mild sedative. Excessive movement can blur MRI images and cause errors.
The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. Ear plugs are usually given to help reduce the noise.
An intercom in the scanner allows you to speak to the person operating the exam at any time. Some MRIs have televisions and special headphones that you can use to help the time pass.
There is no recovery time, unless sedation was necessary. After an MRI scan, you can resume your normal diet, activity, and medications.
Risks
There is no ionizing radiation involved in MRI, and there have been no documented significant side effects of the magnetic fields and radio waves used on the human body to date.
The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. The person operating the machine will monitor your heart rate and breathing as needed.
People have been harmed in MRI machines when they did not remove metal objects from their clothes or when metal objects were left in the room by others.
MRI is usually not recommended for acute trauma situations, because traction and life-support equipment cannot safely enter the scanner area and scan times are relatively lengthy.
What Abnormal Results Mean
The sensitivity of MRI depends, in part, on the experience of the radiologist.
Abdominal MRI may reveal many medical conditions, including:
Additional conditions under which the test may be performed:
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