Contrast Dye Used for X-Rays and CAT Scans

Contrast dye is a solution that is used to accentuate specific structures when looking at a body image. Radiocontrast agents are substances that are used in studies such as X-rays, fluoroscopy, and computed tomography (CT) scans. MRIs use other agents that help to accentuate the magnetic properties of a part of the body.

Doctor preparing patient for MRI
Blend Images - ERproductions Ltd / Getty Images

Radiographic Agents

In X-ray and CT studies, radiocontrast agents are substances that absorb the X-ray photons allow them to be detected by the X-ray film or CT scanner. An example commonly used is the element barium, that is delivered in the compound barium sulfate. Contrast dye can be injected into your blood vessels (to show the vessels), it can be ingested orally (to show the upper gut), or inserted into the rectum (to show the lower gut). In some CT scans, all three types of contrast (so-called "triple contrast") are used.

In orthopedics, the most common use of radiographic agents is to inject the agent into a joint, or space within the body. Often the space is identified with the radiographic agent to confirm a needle is in the proper position before a medication is injected.

MRI Contrast Agents

MRI contrast works differently but also accentuates the differences between tissues. The MRI contrast has magnetic properties and is taken up by some tissues in the body. The altered properties will differentiate tissue types on the MRI image.

The most commonly used MRI contrast agent is the element gadolinium. As with radiographic agents, gadolinium can be injected into the blood vessels or injected into a joint. Gadolinium-enhanced MRI scans can be very helpful at showing subtle findings such as labral tears in the shoulder and hip cartilage damage. Without the contrast agent added, these more subtle findings may not be seen.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Direct Arthrography. Radiological Society of North America, Inc.July 2019.

  2. Zilkens C, Miese F, Jäger M, Bittersohl B, Krauspe R. Magnetic resonance imaging of hip joint cartilage and labrum. Orthop Rev (Pavia). 2011;3(2):e9.  doi:10.4081/or.2011.e9

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.