What is MRI?
Magnetic resonance imaging (MRI) creates a strong magnetic field and employs radio-frequency waves to examine internal organs and tissues. It is used to diagnose a broad range of conditions, including heart disease, stroke, musculoskeletal disorders and diseases of the lungs, kidneys, liver, spleen and pancreas.
How does it work?
Once a magnetic field has been created around the body, radio-frequency waves are directed at protons, the nuclei of atoms within cells. Protons, which are like small magnets, respond to the radio waves by emitting signals that can be mapped to construct internal images of the body. The MRI shows differences in the distribution of water within the tissues.
What does the equipment look like?
Traditional MRI devices are closed cylindrical units into which the patient table slides. Newer MRI "short bore" systems are wider and the tunnel is shorter. Some units are open on all sides.
How should I prepare for the MRI exam?
You will be asked to remove anything that might affect the magnetic field, including jewelry, eyeglasses, hearing aids and removable dental work. Teeth fillings, surgical staples, pins and screws usually do not cause a problem, but tattoos and permanent eyeliner may. As with any test, tell the technician if there is a possibility you may be pregnant.
What will I experience during the exam?
You will lie on a table that slides into the MRI unit and be asked to remain completely still a few seconds or a few minutes at a time during the actual imaging sequences. Some movement between sequences is permitted. The examination generally takes 15-30 minutes.
A contrast material may be injected through an intravenous line placed in a vein in the arm or hand, and may create a cold sensation at the injection site.
The traditional MRI units totally enclose the patient, which can cause claustrophobia. In this case, sedation is helpful. Newer systems reduce the sense of being closed in.
Some people experience a sensation of warmth in the area being examined, which should be reported to the technician if it becomes uncomfortable. The MRI device makes loud knocking and tapping noises at times during the imaging process; if this is a problem, the patient can be provided ear plugs.
Though the technician does not remain in the room during the imaging process, the patient is able to communicate at any time through an intercom.
How will I get the results?
A radiologist, a physician who is trained to interpret medical images, reviews test results before sending them, along with a written report, to your personal physician. Results are usually available within a few days.
What are the benefits and risks of MRI?
Unlike other diagnostic tests, MRI does not use radiation. It allows evaluation of some parts of the body that cannot be seen by any other imaging method but does not always distinguish between a tumor and retained (normal) fluid.
It must be used cautiously in early pregnancy, but other than the chance of slight irritation from the contrast material, it is risk-free except for patients who have cardiac pacemakers, inner ear transplants or aneurysm clips in their brains. MRI is also more expensive than other imaging methods but may reduce the need for invasive procedures.
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