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Quick Facts

Computed Tomography


The Manual's Editorial Staff

Last full review/revision Oct 2019| Content last modified Oct 2019
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What is computed tomography (CT scan)?

A CT scan uses a large machine shaped like a large donut to take x-rays from many angles. A computer then takes the x-rays and creates many detailed pictures of the inside of your body. Each picture looks like a slice taken from one part of your body. The computer can also create a 3-D image of the inside of your body.

  • CT scans are good at showing details of organs and other tissues in your brain, head, neck, chest, and belly

  • CT scans give you more radiation than plain x-rays

Why would I need a CT scan?

Doctors use CT scans for many kinds of problems, including:

  • Problems in your brain and spinal cord, such as bleeding, tumors, or birth defects

  • Problems inside your belly, such as blocked intestines and tumors or infection in your kidneys, liver, or lungs

  • Problems in female reproductive organs, such as tumors in the uterus or ovaries

  • Abnormal blood vessels of your heart or aorta (a large artery connected to your heart)

  • Broken bones, particularly in your hip, back (spine), and pelvis

  • Torn muscles and ligaments

What happens during a CT scan?

Before the scan

Often, you don't need to do anything prior to the CT scan. Sometimes, doctors will give you a liquid (called a contrast agent) through a vein, to swallow, or sometimes inserted in your rear end. The contrast agent makes a certain part of your body show up on the scan more clearly.

During the scan

  • You’ll lie still as the table moves through a large scanner shaped like a donut

  • You may need to hold your breath briefly so that the images aren't blurred

  • You may hear whirring sounds as the scanner moves to take x-rays from many angles

  • A CT scan usually lasts for a few seconds up to a few minutes

After the scan

You can go back to your usual activities.

What are the risks of having a CT scan?


A CT scan exposes you to more radiation than a plain x-ray, like one of your chest. Doctors try to limit the total amount of radiation you're exposed to over your lifetime. Too much radiation can raise your chance of getting cancer.

For pregnant women and children, doctors try to use other tests unless CT is the best way to find a dangerous health problem.

Other problems

  • Some people feel uncomfortable when the contrast agent is injected

  • Some people have an allergic reaction to the contrast agent (such as sneezing, a rash, or trouble breathing)

  • If you have kidney problems (such as kidney failure), the contrast agent can make your problems worse

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