Most patients have very few risks when undergoing an MRI scan.
MRI, or Magnetic Resonance Imaging, is a diagnostic tool that uses magnetic and radio waves to visualize inside the body. The scanning technique has been used since the early 1980s. Because the scan does not use x-ray technology, the patient is not exposed to damaging radiation. MRI creates images of nearly all tissues in the area being scanned, including tissue within bones, so it is particularly useful for diagnosing ailments of the brain or spine. MRI also is the tool of choice when diagnosing heart abnormalities, orthopedic problems and diseases of the internal organs. Very few risks are associated with this method of testing.
Allergic Reaction Risk
In the case of magnetic resonance angiography (MRA), which is used to study arteries and veins, a contrast dye is injected most often through the groin into the femoral vein before the scan takes place. The type of contrast dye most commonly used with MRI is gadolinium. This dye is not recommended for patients with kidney disease because of the risk for nephrogenic systemic fibrosis (NSF). Aside from this risk, gadolinium is used safely in MRA scanning. The risk of allergic reaction to gadolinium is very small, and the technician administering the test closely monitors heart rate and breathing to watch for signs of possible adverse effects. Mild allergic reactions are self-limited and require only antihistamine. More severe reactions that require hospital admission and treatment are extremely rare.
Fetal Damage Risk
Although most studies indicate that MRI during pregnancy is safe, the United States Food and Drug Administration requires MRI devices labeled to indicate that safety to a developing fetus during the first three months of gestation has not been established. Concerns exist related to potential fetal malformation after animal studies have suggested this possibility. Electromagnetic currents used during MRI also carry the possible risk of causing acoustic damage to a first-trimester fetus, although studies are reassuring that this risk is negligible. MRI carries no known risk in second- and third-trimester pregnancies.
Sedative Reaction Risk
Sedatives are not typically used for MRI scanning; however, some patients experience profound anxiety while having to lie motionless within the large metal cylinder used to perform the exam. The machine also makes a loud banging noise throughout the test that might be unnerving for some patients. These patients can be treated with a sedative to help them relax, and in these cases the risks of over-sedation and adverse reaction to the sedative must be taken into account.
Metal Reaction Risk
MRI creates strong magnetic fields, which can interfere with metal. Patients with pacemakers and other metal-containing implants cannot receive MRI and should always stay away from MRI equipment. Patients with clips implanted for aneurysm, artificial heart valves, vascular stents, inner ear implants or artificial joints should work with their physicians to determine if metal is present. Patients who have been exposed to metal in the workplace are given a skull x-ray before MRI to determine if any metal is present in the eyes. No jewelry, hearing aids, pocketknives, eyeglasses or other metal-containing items are allowed in the MRI room. Patients with removable dental work are asked to remove this before the scan.
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