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About Contrast

What is contrast and how does it work?


Contrast agents are used to improve pictures of the anatomy 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.

Contrast materials are not dyes that permanently discolor internal organs. They are substances that temporarily change the way the imaging tools interact with the body. Contrast materials typically are either swallowed or injected into the body in a specific area that is going to be examined to 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. Following an imaging exam with contrast material, the material is absorbed by the body or eliminated through urine or bowel movements.

As leaders in quality care and patient safety, CDI and our partnering radiologists take the utmost care in determining the appropriate use and dosing of contrast agents in all of our procedures.


There are several types of contrast materials:

  • Iodine-based and barium-sulfate compounds are used in X-ray and computed tomography (CT) imaging exams. 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.
  • A gadolinium-based contrast agent may be recommended by your referring provider in some MRI scans to improve the clarity of the images or pictures of your body’s internal structures. If an MRI with contrast is recommended, our radiologist will review your medical history to ensure there are no conditions that might mean a gadolinium injection would not be recommended (e.g. pregnancy, previous allergic reaction, kidney disease). To ensure patient safety, in MRI exams where contrast is indicated, CDI uses an FDA-approved macro-cyclic, ionic structured gadolinium based contrast agent that is widely considered to be among the safest MRI contrast agents available. This agent’s chemical make-up allows it to bind the gadolinium molecule much tighter to itself increasing the ability to fully excrete it from your body through your urine within 24 hours.

How safe are contrast materials?

Contrast materials are used commonly in diagnostic imaging and considered very safe drugs. While some adverse reactions may occur, severe reactions are very uncommon. You will be given exam specific risks and instructions about how to prepare for your exam when you are contacted by our center. As with any medical procedure, we recommend you talk with your physician and radiologist about any concerns you might have.