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Sharper image: CT scanning takes detailed pictures of your body's interior

A CT scan can help doctors diagnose injury or illness by providing detailed images of your body.

Computed tomography is a process that combines x-rays and computers to make images of the body's internal organs and structures. Also known as CT scanning, this technique produces images that are far more detailed than regular x-rays.

How it works

A CT unit is a large machine with a round hole through the center. Inside, on opposite sides of the hole, are an x-ray source and an x-ray detector. The source sends x-rays, and the detector captures them after they pass through your body.

According to the Radiological Society of North America (RSNA) and the U.S. Food and Drug Administration, here's what happens during a CT scan:

  • First, you'll lie on a motorized table that slides into the CT unit. A radiologic technologist will operate the scanner and observe you from a separate room through a window. You will be able to speak to each other using an intercom.
  • When the scan begins, the x-ray source and detector will rotate around you. During each rotation the machine will scan a section of your body, taking pictures from multiple angles. The table may move slightly to put your body in position for the next rotation. You may be asked to hold your breath periodically, since even the slightest movement can blur the image.
  • The pictures are sent to a computer that uses them to create cross-sectional images, or "slices," of the scanned areas of the body. The final images are then analyzed by a radiologist. Your doctor will receive a report of the findings.

CT scans are usually done in a hospital or doctor's office and don't require an overnight hospital stay.

Preparing for a CT scan

Though CT scans are painless and noninvasive, there are a few things to know before you have one.

First, you should tell your doctor if you might be pregnant. If you are pregnant, your healthcare provider will help you weigh the benefits and risks of having the scan.

Your test may include a contrast agent, or dye, to highlight specific areas inside your body. These may be given by mouth, injected into a vein or, uncommonly, given by enema. Although it's rare, these contrast agents sometimes cause allergic reactions. The radiologic technologist will ask if you have allergies, and you should speak up if you feel itchy or short of breath during the procedure.

You will also need to remove all jewelry to prevent the metal from interfering with the imaging.

What a scan can find

According to the RSNA, CT scans may be used to:

  • Check for injuries, tumors or signs of stroke.
  • Determine the stages of some types of cancer and help guide treatment.
  • Examine organs, such as the heart, lungs, liver and kidneys.
  • View bones, such as the spine, and the tissues around them.

Advancing technology

Most CT scanners use an x-ray machine that rotates continuously around your body. These spiral CT scanners take less time than older machines and can provide 3-D images.

For more information about CT scans, including pictures of a CT machine, visit

Reviewed 2/16/2024

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