Contrast media, also known as contrast agents, are chemical substances used in medical imaging exams such as X-rays, computed tomography (CT), magnetic resonance imaging (MRI), angiography, and occasionally ultrasound imaging. They are used to improve the quality of images produced by these exams, allowing radiologists to more accurately diagnose medical conditions by improving the visibility of specific organs, blood vessels, or tissues. Contrast media are not dyes that permanently discolor internal organs, but rather substances that temporarily change the way X-rays or other imaging tools interact with the body.

When introduced into the body prior to an imaging exam, contrast media make certain structures or tissues in the body appear different on the images than they would if no contrast media had been administered. Contrast media help distinguish or “contrast” selected areas of the body from surrounding tissue, highlighting the differences between various parts of the body, including those parts that have a similar composition. Contrast media enter the body in one of four ways: swallowed (taken by mouth or orally), administered by enema (given rectally), injected into a blood vessel (vein or artery; also called given intravenously or intra-arterially), or injected into a cavity of the body (uterus, joints, within the disks or the fluid spaces of the spine, etc.) . Following an imaging exam with contrast media, the media is absorbed by the body or eliminated through urine or bowel movements.

There are several types of contrast media, including iodine-based and barium-sulfate compounds used in X-ray and CT scans, gadolinium-based contrast agents (GBCAs) used for contrast-enhanced MRI scans, and microbubbles used in contrast-enhanced ultrasound. The type of contrast media used depends on the type of imaging test and which body part is being evaluated.

Contrast media are generally safe, but like any medical procedure, there are risks involved. Some people may experience an allergic reaction to the contrast media, and in rare cases, contrast media can cause kidney damage, especially in people with preexisting kidney problems or when large amounts of contrast are used. However, the benefits of using contrast media in medical imaging exams generally outweigh the risks, and healthcare providers take steps to min...