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CT Scans
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Diagnostic Tests

CT Scans

Computed tomography (CT) is a medical imaging test that uses special x-ray equipment to create detailed, cross-sectional pictures of the inside of your body.

What is a CT scan?

Computed tomography (CT) is a type of medical imaging test that uses special x-ray equipment to make detailed pictures of the inside of your body.

A CT scan produces cross-sectional pictures, which are like slices of the body. These images show the size and structure of organs, bones, and other tissues. CT images can also be combined to create 3-dimensional (3D) views. Health care providers use CT scans to diagnose, treat, and monitor many health conditions.

Who needs a CT scan?

Your provider may suggest a CT scan for many reasons, including:

  • Fractures (broken bones)
  • Cancer
  • Tumors or masses
  • Blood clots
  • Signs of heart disease
  • Spinal conditions
  • Lung disease

CT scans may also be used to find the best place to perform a biopsy, help guide certain treatments, check for internal bleeding or injury after trauma, or evaluate the brain for certain conditions.

How do you prepare for a CT scan?

You may be asked not to eat or drink for a few hours before the scan. Ask your provider if there are any special instructions to follow.

For some CT scans, you may receive a contrast material. Contrast helps certain parts of the body show up more clearly on the images. Depending on what area is being examined, contrast material might be given as:

  • A liquid to swallow
  • A shot (injection)
  • An enema (placed into the rectum)

CT scans use ionizing radiation at levels higher than a standard x-ray, but the amount is kept as low as possible. Always tell your provider if you are pregnant or think you may be pregnant.

How is a CT scan done?

You may be asked to change clothes and remove jewelry or other items that could interfere with the scan. During the scan, you lie still on a table. The table slowly passes through the center of a large donut-shaped machine. The x-ray tube rotates around your body to create images.

You may hear whirring sounds during the scan. You may be asked to hold your breath for short periods. The test is painless. The scan usually takes a few minutes, but some may last up to 30 minutes, depending on the area being scanned.

What should you expect after a CT scan?

Most people can return to normal activities right away. If you were given a contrast material, drinking fluids can help your body clear it. A specialist called a radiologist reviews the images and shares the results with your provider.

Frequently Asked Questions

Intravenous contrast dye can cause a harmless warm sensation or metallic taste, but some individuals experience allergic reactions such as hives, itching, or rarely, severe breathing difficulties. Patients with preexisting kidney disease face a risk of contrast-induced kidney damage. Always notify your healthcare team if you have renal impairment, diabetes, asthma, or a history of allergic reactions to contrast material.
CT scan delivers significantly more radiation than a plain X-ray because it takes hundreds of cross-sectional exposures to build a detailed image. A single chest CT delivers a radiation dose equivalent to approximately 100 to 200 standard chest X-rays. While this increases cumulative lifetime radiation exposure slightly, the immediate diagnostic benefit usually far outweighs the theoretical risk.
Yes. Unlike an MRI, which uses powerful magnetic fields, CT scans utilize X-rays and are safe for patients with pacemakers, artificial joints, surgical clips, and metal hardware. However, metal can create visual distortion or "streaking" artifacts on the images, so notify the technologist of any implants beforehand.
Fasting for 2 to 4 hours before receiving IV contrast reduces the risk of nausea and vomiting, which are common transient side effects of the dye. Having an empty stomach prevents the dangerous risk of aspirating stomach contents into the lungs while lying flat inside the scanner.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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