Magnetic resonance imaging, or MRI, is a relatively safe technique for taking three-dimensional images anywhere in the body, according to the Mayo Clinic. The technique uses a magnetic field and radio waves to create highly detailed images that can help diagnose a variety of illnesses. An MRI is essentially a huge and powerful magnet that temporarily aligns some of the subatomic particles in a person's body. Radio waves are then aimed at the body, which causes the aligned molecules to emit a signal that is used to create the image.
General Risks
Because an MRI doesn't use X-rays or other kinds of radiation, there are few risks to it for most people, according to the Mayo Clinic. There are no known health problems caused by either the magnetic field or the radio waves employed by an MRI. Unlike X-rays, there isn't a cumulative effect, either. There are no known long-term risks to MRI scans. However, if a patient is pregnant, she's often advised to delay having an MRI or use another imaging technique because the effect of magnetic fields on the fetus is not well understood.
Metal Risks
Because the MRI is such a strong magnet, there is risk to anyone who has metal inside his body. The magnet could shift the metal or even yank it out of the person at high speed, causing tissue damage, according to the Mayo Clinic. For this reason, a patient undergoing MRI is carefully screened to ensure he has no metal on him or any jewelry, watches, hairpins, hearing aids or underwire bras. People who have metal or electronic devices implanted, such as artificial joints or heart valves, pacemakers, or cochlear implants, should tell the MRI technician. In some cases these devices can be shielded to prevent injury, but sometimes an MRI cannot be used on these patients. This also applies to people who have bullets or other metal shrapnel embedded in their bodies, which can shift during the test and cause injury. Pacemakers and hearing aids can be damaged during the test by the magnet. Even makeup can cause problems because sometimes it contains small amounts of metals, according to the International Society for Magnetic Resonance in Medicine.
Contrast Risks
A contrast agent called gadolinium that helps create a clearer picture is sometimes injected into patients having an MRI. That can pose risks in rare cases, according to the International Society for Magnetic Resonance in Medicine. Some people have an allergic reaction to the agent, which can be life threatening. MRI technicians are equipped and trained to treat such reactions. Also, people with kidney or liver problems should tell their doctor and the MRI technician because the contrast agent could cause problems, according to the Mayo Clinic.
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