Magnetic resonance imaging (MRI) employs powerful magnets and radio waves to produce three-dimensional images of the body. It is particularly useful for imaging the soft tissues of the body. Depending on the reason for the MRI, a contrast agent is sometimes used to enhance the quality of the images. When contrast is used, scanning is usually done before and after the agent is given. This enables the radiologist to compare the images with and without contrast, which aids in interpreting the findings. MRI contrast agents uncommonly cause side effects, most of which are mild and temporary. Serious side effects due to MRI contrast are rare.
Most Frequent Side Effects
Most MRI contrast agents are gadolinium-based chemicals. A 2016 report from the American College of Radiology states that side effects occur in 0.7 to 2.4 percent of MRIs employing gadolinium-based contrast. Most side effects are mild and temporary, and include:
-- warmth, coolness or pain at the injection site
-- nausea, with or without vomiting
-- an odd taste in the mouth
-- brief muscle twitching
Most people do not require treatment for these side effects, which usually go away on their own within a few minutes to hours.
Allergic reactions to MRI contrast agents are rare. According to the American College of Radiology, allergy-like reactions to gadolinium-based contrast agents occur with 0.004 to 0.7 percent of injections. Most of these reactions are mild, such as hives, itchiness, a scratchy throat, sneezing, nasal stuffiness, itchy or watery eyes, and redness around the injection site. Moderate allergy-like reactions occur less frequently and might include temporary shortness of breath, mild facial swelling and widespread skin redness. These reactions might require medication, such as an antihistamine, but typically do not pose a serious health threat.
Severe allergic reactions to gadolinium-based contrast agents are quite rare. A hallmark study published in November 1999 in the journal "Academic Radiology" found that out of more than 825,000 MRIs involving gadolinium contrast, only 16 severe allergic reactions occurred. Although rare, these reactions are potentially life-threatening and require urgent treatment. Possible signs and symptoms include airway swelling, wheezing, severe shortness of breath, low blood pressure, seizures, loss of consciousness and heart rhythm abnormalities. Severe allergic reactions to gadolinium-based contrast agents almost always occur within an hour after injection.
Nephrogenic Systemic Fibrosis
Nephrogenic systemic fibrosis (NSF) is a rare condition characterized by an accumulation of scar tissue primarily in the skin and to a lesser extent in the lungs, muscles, heart and esophagus. Nearly all described cases of NSF have occurred in people with severely limited kidney function who have been received gadolinium-based contrast. Since the kidneys are responsible for clearing gadolinium from the body, people with severely limited kidney function retain the metal in their body for a prolonged period. This can trigger the development of NSF as early as a few weeks after exposure. Importantly, people with normal or only mildly impaired kidney function are not at risk for NSF due to gadolinium-based contrast exposure.
NSF signs and symptoms include firm, red or dark colored, swollen skin patches. These patches typically begin on the lower legs and may eventually spread to the arms. Skin affected by NSF is often painful and very itchy. The skin scarring can lead to joint stiffness and difficulty moving. Muscle weakness, bone pain and yellow spots on the whites of the eyes also often occur. Internal organ involvement leads to other, varied symptoms. There is no known cure for NSF, which can be life-threatening in severe cases.
Warnings and Precautions
MRI contrast agents are considered safe and pose fewer risks than CT contrast, overall. However, as with any drug or substance injected into the body, side effects are possible. If you are scheduled to undergo an MRI with contrast, let your doctor and radiologist know if you have kidney disease or risk factors for kidney disease, including high blood pressure and diabetes. Also notify the radiologist if you have allergies or asthma, or if you've previously experienced any type of reaction to MRI contrast in the past as your risk for side effects may be increased.
Reviewed and revised by: Tina M. St. John, M.D.