CT Scan - What to Expect

This information was reprinted with permission. © 2008 American Society of Clinical Oncology. All rights reserved. www.Cancer.net.

A computed tomography (CT) scan, also called a CAT scan, is a diagnostic exam used to detect tumors, determine the stage of the disease and whether cancerous cells have spread, and find out about the effectiveness of cancer treatment. CT scans are also used to guide some types of biopsies (the removal of a small amount of tissue for examination to determine whether cancer is present). Common areas that may be scanned include the head, neck, chest, abdomen, pelvis, or an extremity.

The CT scanner takes a series of x-ray pictures, which are combined by a computer to create extremely detailed, cross-sectional images of your internal organs or other parts of your body that cannot be examined with conventional x-rays.

The medical team

A CT scan is performed at the radiology department of a hospital or at an outpatient imaging center. It is performed by a radiologist or radiology technologist who specializes in CT imaging. A radiologist is a medical doctor who performs and interprets imaging tests to diagnose disease. A radiology technologist is specially trained and certified to operate a CT scanner.

Questions to ask your doctor

Before having a CT scan, consider asking your doctor 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?
  • Are there risks of having a CT scan?
  • What are the risks of not having the test?
  • Do I need to bring any of my other radiologic images (for example, from an earlier magnetic resonance imaging [MRI] test) to my appointment?
  • Is the imaging facility accredited to perform CT scans?
  • Will I be given a contrast agent (dye) before the scan? If so, how will this be given to me?
  • May I eat or drink anything prior to the exam?
  • Does the facility have an emergency response plan, in case I have an allergic reaction to the contrast material 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?
  • Who will explain the results to me?
  • What further tests will be necessary if the scan results indicate cancer?

Preparing for the procedure

When you schedule the examination, you will get detailed instructions on how to prepare.

Review with your doctor or nurse whether you should take your regular medications that day. In addition, tell your doctor about all medications you are taking, any drug allergies you have, and especially any allergic reactions you've had to iodine. In addition, be sure to mention any other medical conditions you have.

Women should tell their doctors if they are breast-feeding, or if there is any chance that they are pregnant.  You may be told to drink only clear liquids starting at midnight the night before your examination. You will usually also be instructed to not eat or drink anything for at least four hours prior to your scan. However, for scans of some parts of the body, there will not be restrictions on eating prior to the examination.

Wear loose, comfortable clothing. Try to wear a shirt without snaps or zippers, which may interfere with the scan. Leave jewelry at home; you will most likely have to remove it for the scan.

Ask whether you can bring your own music; some facilities allow patients to listen to music during their examinations.  You will be asked to sign a consent form that states you understand the benefits and risks of the CT scan and agree to have the test done. Talk with your doctor about any concerns you have about the CT scan.

During the procedure

When you arrive for your CT scan, you may need to change into a hospital gown. Or, you may need to remove certain pieces of clothing or jewelry that will interfere with the scan. This includes belts, earrings, shirts with snaps or zippers, bras, and glasses.

You may receive a contrast agent depending on the part of the body to be scanned. This may be given to you as a drink, as an injection into the vein (called intravenous [IV] injection). The dye travels through your bloodstream and helps to 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; both sensations should disappear after a few minutes. If you experience a more serious reaction, tell the technologist immediately.

A technologist will help position you on an exam table. The table may have straps or pillows to help hold you in place or a special cradle for your head. You will probably lie on your back, though you may be asked to lie on your side or your stomach, depending on the part of your body being scanned, especially if you are undergoing a biopsy.

During the examination, the technologist who monitors the procedure will be in an adjoining control room, but he or she will be able to observe you through a window or by means of a video camera, and you will be able to communicate through an intercom system.

The CT scanner resembles 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. For the first scans, the table will move rapidly through the scanner; these help the technologist confirm that your body is properly positioned. For the remaining scans, the table will move more slowly.

CT scans are not painful. 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 will hear whirring or clicking sounds from the machine; some machines are noisier than others. You may be asked to hold your breath during part of the scan because the motion created by breathing can blur the images. The exam table may be raised, lowered, or tilted to create the correct angle for the x-rays; ask the technologist performing the scan to tell you when the table will move.

The examination will generally last up to an hour, though 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 procedure 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 if additional images are needed.

After the procedure

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