What are contrast materials and how do they work?

Contrast materials, also called contrast agents or contrast media, are used to improve pictures of the inside of the body produced by x-rays, computed tomography (CT), magnetic resonance (MR) imaging, and ultrasound. Often, contrast materials allow the radiologist to distinguish normal from abnormal conditions.

1. To show differences when compared: siblings who contrast sharply in interests and abilities; a color that contrasted clearly with the dark background.
2. Contraste translate: contrast, with high contrast, contrast, contrast. Learn more in the Cambridge French-English Dictionary.
3. Contrast definition, to compare in order to show unlikeness or differences; note the opposite natures, purposes, etc., of: Contrast the political rights of Romans and Greeks.

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Contrast materials are not dyes that permanently discolor internal organs. They are 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 materials make certain structures or tissues in the body appear different on the images than they would if no contrast material had been administered. Contrast materials help distinguish or 'contrast' selected areas of the body from surrounding tissue. By improving the visibility of specific organs, blood vessels or tissues, contrast materials help physicians diagnose medical conditions.

Contrast materials enter the body in one of three ways. They can be:

• 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)

Following an imaging exam with contrast material, the material is absorbed by the body or eliminated through urine or bowel movements.

There are several types of contrast materials:

• Iodine-based and barium-sulfate compounds are used in x-ray and computed tomography (CT) imaging exams.

Contrast materials can have a chemical structure that includes iodine, a naturally occurring chemical element. These contrast materials can be injected into veins or arteries, within the disks or the fluid spaces of the spine, and into other body cavities.

Barium-sulfate is the most common contrast material taken by mouth, or orally. It is also used rectally and is available in several forms, including:

• powder, which is mixed with water before administration
• liquid
• paste
• tablet

When iodine-based and barium-sulfate contrast materials are present in a specific area of the body, they block or limit the ability of x-rays to pass through. As a result, blood vessels, organs and other body tissue that temporarily contain iodine-based or barium compounds change their appearance on x-ray or CT images.

• Gadolinium is the key component of the contrast material most often used in magnetic resonance (MR) exams. When this substance is present in the body, it alters the magnetic properties of nearby water molecules, which enhances the quality of MR images.
• Saline (salt water) and gas (such as air) are also used as contrast materials in imaging exams. Microbubbles and microspheres have been administered for ultrasound imaging exams, particularly exams of the heart.

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