Also referred to as contrast agent or contrast medium.

Any internally administered substance that has a different opacity from soft tissue on radiography or computed tomography. Includes:

• Barium or water used to make parts of the gastrointestinal tract clearer.
• Iodine in water used for arthrography.
• Water soluble iodine, used to make blood vessels clearer. Demonstrates the inner structures of the urinary tract (kidneys, ureters and bladder). Outlines joints (the spaces between two bones).
• Iodine mixed with water or oil may be used to evaluate the fallopian tubes and lining of the uterus.
• Sterile saline (salt water) is used during hysterosonography.
• May refer to air in the body.
• Paramagnetic substances used in magnetic resonance imaging. 

For more information see the Contrast Materials page.