Computed Tomography (CT) Scan

Approved by the Cancer.Net Editorial Board, 07/2018

Listen to the Cancer.Net Podcast: CT Scan - What to Expect, adapted from this content.

Doctors use a computed tomography (CT) scan, also called a CAT scan, to find cancer. They also use it to learn more about the cancer after they find it. More specifically, they can use it to:

  • Learn the cancer’s stage. Knowing this helps you and your doctor choose the best treatment options. It also helps doctors predict your chance of recovery.

  • Find the right place for a biopsy.

  • Plan radiation therapy.

  • Evaluate how well treatment is working during follow-up visits.

  • Evaluate how well treatment worked after it ends and during follow-up care.

How does a CT scan work?

A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer then combines these images into a detailed, 3-dimensional image that shows any abnormalities or tumors. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill or liquid to swallow.

Areas that are commonly scanned include the head, neck, chest, abdomen, pelvis, or limbs. A total body CT scan generally includes at least the chest, abdomen, and pelvis. This is often used for cancer staging.

One risk of this test is radiation exposure, especially for children. But the potential benefits of having a CT scan usually outweigh the risks. Also, low-dose CT scans are now being used in many cases for children. If you are receiving multiple CT scans and x-rays, talk with your health care team about using another type of test that involves less exposure to radiation.

An integrated PET-CT scan

Your doctor might recommend an integrated PET-CT scan. This combines images from a PET scan and a CT scan. The machine does both scans at once. Your doctor learns more from the 2 scans together than from either test alone.

Who does my CT scan?

A CT scan is done at the radiology or radiation oncology center of a hospital or at an outpatient imaging center. It is performed by a radiologic technologist and interpreted by a radiologist.

Getting ready for a CT scan

When you schedule your CT scan, you will get detailed instructions about how to prepare.

What to eat. You may be told to drink only clear liquids starting at midnight the night before your appointment. You may also be asked not to eat or drink anything for at least 4 hours before your scan begins. Talk with your health care team about restrictions on eating and drinking because they may not be necessary for scans of some parts of the body.

If you need contrast medium for the scan. If you will be receiving a contrast medium through an IV, you may need to have a blood test to check your kidney function. This can be done any time up to a few weeks before the scan.

Topics to discuss with your health care team. Be prepared to discuss the following topics with your health care team:

  • All medications you are taking

  • Any drug or food allergies you have, especially any allergic reactions to iodine you may have experienced in the past

  • Whether you should take your usual medications on the day of the procedure

  • Any medical conditions you have, such as diabetes

  • If you are breastfeeding or if there is any chance you are pregnant because a CT scan could put the baby at risk.

  • Any concerns you may have about the test

Insurance, costs, and consent. Before your appointment, find out from your insurance provider what costs will be covered. Ask how much of the cost you will have to pay. Once you arrive at the doctor's office or hospital, you will be asked to sign a consent form. This form states that you understand the benefits and risks of the procedure and that you agree to have it.

During the procedure

When you arrive for your CT scan, you may need to change into a hospital gown or remove clothing or accessories that could affect the scan. This includes belts, earrings, shirts with snaps or zippers, bras, and glasses.

Depending on which part of your body is being scanned, you may be given a contrast medium. The dye travels through your bloodstream and helps create a clearer picture of specific parts of your body.

If you are given an injection, you may feel heat or itching at the injection site or have a metallic taste in your mouth. But both sensations should disappear after a few minutes. If you experience a more serious reaction, like trouble breathing, tell the technologist immediately.

The technologist will help position you on an exam table. The table may have straps, pillows, or a special cradle for your head to hold you in place. You will probably lie on your back, but the technologist may ask you to lie on your side or your stomach. This will depend on which part of your body is being scanned. If the scan is done as a part of planning for radiation therapy, there may be special devices such as masks or body casts to keep your body in the same position for the treatment.

The CT scanner looks like a large donut. The exam table will slide back and forth through the large hole in the center of the machine as the scanner rotates around you. At first, the table will move through the scanner quickly. This helps the technologist confirm that your body is in the right position. After that, the table will move more slowly.

CT scans are not painful. But you will need to lie still for the entire scan, which may become uncomfortable. Since the scanner is shaped like a donut, you will not be enclosed in the scanner at any time. You can also expect to hear whirring or clicking sounds from the machine. Some machines are noisier than others.

During the scan, the technologist will be in a nearby control room. He or she will be able to see you through a window or a video camera. And you will be able to communicate through an intercom system.

The technologist may ask you to hold your breath during part of the scan because movement from breathing can blur the images. He or she may raise, lower, or tilt the exam table to create the correct angle for the x-rays. Ask him or her to tell you when the table will move.

The exam will typically last up to 1 hour. The scanning itself takes only 10 to 15 minutes or less. Newer scanners, including spiral or helical CT scanners, are even faster. If a larger part of your body is being scanned, the test may last longer. The technologist should be able to give you a time estimate before you begin.

When the scan is finished, you may be asked to remain on the exam table while a radiologist reviews the images to determine whether more images are needed.

After the procedure

You can return to your normal activities immediately after your CT scan, including driving. If you received a contrast medium for the scan, you may be told to drink a lot of water to flush it out of your body.

Questions to ask your health care team

Before having a CT scan, consider asking your health care team the following questions:

  • What will happen during the CT scan?

  • Who will perform the CT scan?

  • How long will the procedure take?

  • Will there be any discomfort?

  • Can I bring my own music to listen to during the scan so I can feel more comfortable?

  • What are the risks and benefits of having a CT scan?

  • Do I need to bring any of my other radiologic images, such as an earlier magnetic resonance imaging (MRI) test, to my appointment?

  • Is the imaging center accredited to perform CT scans?

  • Will I be given a contrast medium before the scan? If so, how will it be given?

  • May I eat or drink anything before the exam?

  • Does the center have an emergency response plan in case I have an allergic reaction to the dye used for the scan?

  • Will I need to avoid any activities after the CT scan?

  • When will I learn the results?

  • How will the results be communicated to me?

  • Will I need any additional tests?

Related Resources

Cancer.Net Podcast: Coping with "Scanxiety"

More Information

National Cancer Institute: Computed Tomography (CT) Scans and Cancer Computed Tomography (CT) - Body