Health Library

CT Scan (General)


A CT scan combines a series of x-rays to make a complete picture. It can take images of bone, blood vessels, and soft tissue at different angles. It can make more detailed pictures than regular x-rays .

CT Scan of the Head
Breast self-exam, step 5
Copyright © Nucleus Medical Media, Inc.

Reasons for test

CT scans can help to:

  • Diagnose muscle and bone disorders, such as bone tumors and fractures
  • Pinpoint the location of a tumor, infection or blood clot
  • Guide procedures such as surgery, biopsies, and radiation therapy
  • Detect and monitor diseases and conditions such as cancer, heart disease, lung nodules and liver masses
  • Monitor the effectiveness of certain treatments, such as cancer treatment
  • Detect internal injuries and internal bleeding

Possible Complications

You are exposed to some radiation during a CT scan. It is a higher amount than regular x-ray but still very low. 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 doctor if you are pregnant or may be pregnant. A CT scan will probably not harm the unborn child but there may be other safer choices.

A special dye called contrast material may be used. It helps to make a clearer picture of one area. Some may have an allergic reaction to this dye, 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 severe allergic reaction to anything. If you are given a contrast dye, you may have an increased risk of problems if you also have:

Talk to your doctor about these risks before the test.

What to Expect

Prior to Test

Depending on which part of your body is being scanned, you may be asked to:

  • Take off some or all of your clothing and wear a hospital gown
  • Remove metal objects, such as a belt, jewelry, dentures and eyeglasses, which might interfere with image results
  • Refrain from eating or drinking for a few hours before your scan

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

  • Drink—common for scans of esophagus or stomach
  • Injection—for scans of gallbladder, urinary tract, liver or blood vessels
  • Enema—delivered through 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, motorized 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.

While the table moves you into the scanner, detectors and the X-ray tube rotate around you. Each rotation yields several images of thin slices 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 communicate with the technologist via intercom. The technologist may ask you to hold your breath at certain points to avoid blurring the images.

After Test

You may be asked to wait for a short time to make sure you feel well after the exam. After the exam you can return to your normal routine.

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 contrast material is injected into your vein. The enema contract 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 Resources

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.