Contrast Medium (Contrast)

Author: Courtney Misher, MPH, BS R.T.(T)
Last Reviewed: December 12, 2022

Contrast allows your provider to better see what is happening inside your body during an imaging exam. Imaging exams that can be done with contrast are x-ray, computed tomography (CT), ultrasound, magnetic resonance (MRI), and fluoroscopy. Contrast, often called dye, does not actually dye your organs or blood vessels. The contrast moves through your body during your imaging test and then is removed from your body through your urine and stool.

How is contrast given?

There are three main ways that contrast is given, and each looks at different parts of the body:

  • Intravenously (IV): Given into your vein. It is often used to look at your brain, spine, liver, and kidneys.
  • Orally: Swallowed by mouth. It is often used to look at your abdomen (stomach area) and pelvis (bowel area).
  • Rectally: Given by enema through a rectal tube to look at your large intestine, rectum, colon, and other organs in the pelvis.

Sometimes you will be given both IV and oral contrast. This is done so your provider can better see your organs, vessels, and tissues on the images.

How do I prepare for contrast?

You may be given instructions about how to prepare for your test with contrast like getting labs drawn to check your kidney function or not eating or drinking. It is important to follow these instructions.

Let your care team know before you arrive for your appointment if you have an iodine allergy or if you have ever had an allergic reaction to contrast. You may be given special instructions or medications.

What can I expect when having contrast?

The timing of when you are given contrast will depend on the type of contrast being used. Your body may feel different in the minutes after being given contrast. It is helpful to know what to expect. You can expect the following:

  • IV contrast: Is given either before or during the imaging test. It does not hurt, but you may feel warm or flushed after it is given, followed by a salty or metallic taste in your mouth. You may also feel like you need to urinate. These are all normal.
  • Oral contrast: Is given before your scan. It may be given up to 90 mins before, depending on the area of your body that it being looked at.
  • Rectal contrast: A provider will administer rectal contrast using an enema. You may feel like you are bloated or like you need to have a bowel movement, but this feeling will go away.

Some people are allergic to contrast. If you feel symptoms such as itching, headache, dizziness, trouble breathing or swallowing, nausea and/or vomiting let your care team know right away.

What can I expect after having contrast?

You can go back to your normal day after being given contrast, but you may be asked to drink extra fluids to help remove the contrast from your body.

If you have diabetes and take Metformin you may need to follow special instructions after getting IV contrast. Your care team will give you the instructions.

If you have any questions about the use of contrast during your imaging test, talk with your provider.

Computed Tomography (CT) SCAN. Cancer.Net. (2022, July 15). Retrieved December 12, 2022, from

CT Scan for cancer. American Cancer Society. (2015, November 30). Retrieved December 12, 2022, from

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