Contrast agents help illuminate body tissues and organs during a CT scan.
Contrast agents or materials are substances a radiology technologist may administer during a medical test to help better view the tissues and structures in your body. Commonly used in a computed tomography (CT) scans or magnetic resonance imaging (MRI) tests, contrast agents can help doctors diagnose certain medical conditions. While a severe reaction from the substances are uncommon, side effects and adverse reactions are possible.
How They Work
Contrast materials highlight or contrast certain tissues or structures of the body from its surroundings during a medical test. In a CT scan, which uses X-rays and computer technology to produce cross-sectional images of your body, the agents absorb or block X-rays so organs are more visible on CT images. In an MRI test, contrast agents alter the magnetic properties of water molecules in your body, which improves the visibility of tissues and the quality of the images. An MRI test uses high frequency radio waves and strong magnetic fields to produce clear pictures of structures in your body.
Types and Uses
The type of medical test performed and body part examined determine what type of contrast material radiology technologists use. Barium sulfate and iodine-based compounds are the most commonly used contrast materials as part of a CT scan. Barium sulfate, available in tablet or liquid form, or as an enema, enhances images of the gastrointestinal tract, which includes the stomach, colon and esophagus. Iodine-based contrasts are clear liquids doctors inject into a blood vessel to get a better picture of the vessels, your gallbladder, spleen, urinary tract and bile duct.
In an MRI, injected gadolinium-based contrasts help provide doctors with improved images of your brain, internal organs such as your heart, kidneys or lungs, arteries, veins and soft tissues.
Side Effects
In general, contrast materials are safe. However, mild side effects may occur and, in severe and rare cases, an allergic or adverse reaction. A barium sulfate contrast may leave you with an unpleasant taste in your mouth when given orally or a feeling of bloating when given rectally. Additional side effects of the contrast include vomiting, constipation, nausea, diarrhea and stomach cramps. Iodine-based materials can leave a metallic taste in your mouth, cause bruising at the site of injection, itching, headache, nausea, flushing, vomiting or hives.
Gadolinium contrast agents usually have no side effects and are less likely to cause an allergic reaction than iodine or barium sulfate agents. A review of severe reactions of patients at two hospitals over a 10-year period by Martin R. Prince and colleagues in the February 2011 issue of the "American Journal of Roentgenology," found patients who had a serious reaction to a gadolinium-based contrast had a history of previous reactions to the agent.
Risk Factors
If you have heart disease, diabetes, kidney disease, allergy, asthma, are dehydrated, or a have a history of reaction to contrast materials, you may be at higher risk of developing a severe or allergic reaction to a contrast material. Talk to your doctor about any medications and conditions you have before your test.
Warning
If you have kidney disease, are pregnant or taking diabetes medication, speak to your doctor about the risks of contrast agents. Iodine-based materials can cause kidney failure in some patients, especially if you are taking a diabetic medication known as Glucophage, MedlinePlus notes. If you have severe kidney disease, gadolinium contrast agents may increase your risk of nephrogenic systemic fibrosis, a disease that causes thickening of the organs, tissues and skin.
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