by McCoy K
(Computed Tomography Scan; Computed Axial Tomography; CAT Scan)


A CT scan is a machine that takes a series of x-rays to make a picture with many details. It can take images of bone, blood vessels, and soft tissue at different angles. It makes more detailed pictures than regular x-rays.

CT Scan of the Head
Breast self-exam, step 5
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Reasons for test

CT scans can help to:

  • Diagnose muscle and bone problems, such as bone tumors and fractures
  • Show exactly where a tumor, infection or blood clot is located
  • Guide doctors during procedures such as surgery, biopsies, and radiation therapy
  • Detect and track issues such as cancer, heart disease, lung nodules and liver masses
  • Monitor how well treatments are working, such as cancer treatment
  • Look for signs of internal injuries and bleeding

Possible Complications

There is some radiation exposure during a CT scan. It is very low but higher than radiation from regular x-rays. This level of radiation has not been shown to cause long-term harm. Talk to your doctor about the risks and benefits of CT scan for you.

Tell the care team if you are pregnant or may be pregnant. A CT scan will probably not harm an unborn child but there may be safer choices.

A special dye called contrast material may be used. It helps to make a clearer picture of one area. The dye can cause an allergic reaction, but it is rare. Allergic reaction can range from mild rash or itching to serious, life-threatening event. Tell your doctor if you have had an allergic reaction to dye or any severe allergic reaction.

Talk to your doctor about these risks before the test.

What to Expect

Prior to Test

You may be asked to:

  • Take off or adjust clothing. You may need to wear a hospital gown
  • Remove metal objects, such as a belt, jewelry, dentures and eyeglasses. They might cause problems with images.
  • Avoid food or drink for a few hours before your scan.

You may be given a contrast dye. It may be given through:

  • Drink—common for scans of throat or stomach
  • Injection—for scans of gallbladder, urinary tract, liver, or blood vessels
  • Enema—inserted in rectum for scans of intestines

Description of the Test

CT scanners are shaped like a large doughnut standing on its side. You lie on a narrow, table that slides through the opening into a tunnel. Straps and pillows may be used to help you stay in position. During a head scan, the table may be fitted with a special cradle that holds your head still.

The table slides into the scanner while detectors and the X-ray tube rotate around you. Each rotation makes several images of your body. You may hear buzzing and whirring noises.

A tech in a separate room can see and hear you. You will be able to talk to them throughout the test. You may need to hold your breath at some points to prevent blurred images.

After Test

You may be asked to wait for a short time right after the exam. You can return to your normal routine once you leave.

How Long Will It Take?

About 10 to 15 minutes for the scan. New machines may take less time. You may be at the site for about 30 minutes all together.

Will It Hurt?

You may feel warm and flushed if a contrast material is injected. It should pass within a few minutes. The enema contrast can cause some bloating in the belly.


The CT images will be sent to a radiologist who will study them. Your doctor will get the results and talk about them with you.

Call Your Doctor

Call your doctor if you have:

  • Symptoms of allergic reaction, such as hives , itching, nausea, swollen or itchy eyes, tight throat, or problems breathing
  • Any other problems

If you think you have an emergency, call for emergency medical services right away.


NIH Clinical Center 

Radiology Info—Radiological Society of North America 


Canadian Association of Radiologists 

Canadian Radiation Protection Association 


Computed tomography (CT)—body. Radiology Info—Radiological Society of North America website. Available at: Accessed January 26, 2021.

Radiation-emitting products: computed tomography (CT). US Food & Drug Administration website. Available at: Accessed January 26, 2021.

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