Medical Imaging Contrast: What is It, and What Does It Do?

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If your doctor has ordered you to have a medical imaging exam, you may have a test that uses contrast materials. Medical Imaging Contrast is a substance radiologists use that acts like a dye. But receiving contrast dye isn’t like going to the hairstylist—it won’t change the color of your organs and bones!

What is Medical Imaging Contrast?

Medical imaging contrast—sometimes referred to as contrast dye or contrast materials—is a substance that radiologists use to see your organs and tissues more clearly in your medical images. It’s kind of like a dye in the way that it temporarily changes how your insides appear on a medical image, but it won’t change the color of anything and it won’t hurt you.

You might need contrast when you are having an X-ray, CT, MRI, or ultrasound exam. It can be an iodine-based material, barium-sulfate, gadolinium, or saline and air mixture that can be swallowed or injected intravenously.

Contrast distinguishes, or “contrasts,” between organs, tissues, bones, or blood vessels during your imaging exam. It doesn’t change any of these things, but it changes how your X-ray, CT, or MRI scan sees them.

If you need contrast, your exam will probably take longer than if you weren’t having contrast. For example, it could add four hours of prep time to a five-minute CT scan or make a thirty-minute MRI last two hours. This is because of the time it takes to administer the contrast and for it to start working. Although it takes longer, the clearer images it provides for your doctor are worth the wait.

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Why is Contrast Important?

Contrast is important because it helps radiologists distinguish between normal and abnormal conditions. This helps them to see what’s going on inside of you better. In turn, this allows them to make a more accurate diagnosis, and recommend the best treatment for your specific case. In cases where it is needed, contrast ultimately leads to better care.


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How Does It Work?

Contrast can be swallowed as a drink or injected into a vein. The kind of exam you are receiving will determine what kind of contrast you’ll need. It will also determine how it needs to be administered (orally or intravenously). Your body will naturally absorb or eliminate the contrast materials after your exam.

Contrast materials work by using substances that interfere with how the medical imaging equipment takes your images. For example, the contrast used in an X-ray or CT exam is made of a substance that will block or limit radiation in certain parts of your body. This changes how the tissues that contain the medical imaging contrast appear on your images. Similarly, contrasts used in magnetic-powered exams like MRIs and ultrasounds alter the way magnetic fields interact with the parts of the body containing contrast. So, contrast doesn’t alter anything inside of you, it only alters the way medical imaging equipment sees the inside of you.


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Is Medical Imaging Contrast Risky?

In rare cases, people have allergic reactions to contrast materials. It is crucial that you communicate well with your doctor. Tell them about any allergies, recent illnesses, or medications you have. If you have a known contrast allergy—or are at risk—the hospital staff will take every precaution to protect you from a negative reaction.

Rarely, patients face mild side effects from medical imaging contrast like nausea and diarrhea. But most people do not react at all. If you’re receiving contrast dyes for your medical imaging exam, be sure to drink plenty of water afterwards. Your body will expel the contrast naturally.

To learn more about two common procedures that use contrast materials, take a look at our article on MRI vs. CT. If you’re interested in getting a screening done at the UVA Health System, call 1.434.243.0321 to set up a consultation today.

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