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CT Scanning

What is CT scanning?

CT scanning, also called computed tomography or computerized axial tomography (CAT scan), is an X-ray test used for diagnosis. X-rays are taken from a series of different angles and arranged by a computer to show a cross-sectional view of organs in the body.

When is it used?

CT scanning is used when your healthcare provider needs more detailed information than regular X-rays provide. CT scans are especially useful for identifying tumors and cysts.

How do I prepare for a CT scan?

For most scans no preparation is necessary. Your healthcare provider will give you special instructions, if needed. For example, if you are having a CT scan of your abdomen or pelvis, you should not eat solid food for several hours before the scan.


You should wear comfortable clothing that has no metal fastenings like zippers or hooks. Leave your watch and jewelry at home. You may be asked to wear a hospital gown, but if not, you'll be properly dressed for the scan.

What happens during the procedure?

CT scanning can be done in either a hospital or mobile unit. You will lie down on a moving table, which will slide you into the tunnel-like scanning machine. The scanner can move around you to change the angles of the X-rays.


Inside the scanner, multiple X-ray beams are passed very quickly through your body at different angles. The images are projected onto a TV screen and prepared for your healthcare provider to examine.


A solution of dye (also called contrast) may be injected into a vein, or you may be asked to swallow the solution. This allows the scanner to show any abnormal areas as the dye passes through your body.


Scans may last 15 to 90 minutes. They are painless, but you may get uncomfortable from lying in the scanner if the scan takes more than a few minutes. You can talk to the technologist at any time during the procedure. Because of the small, enclosed space, some people become anxious. If you start feeling panicky, the procedure may be stopped. Your healthcare provider may recommend a mild sedative to help you relax.

What happens after the procedure?

If you were given dye for the scan, drinking a lot of fluids after the procedure may help your body get rid of the dye. Rarely some people have an allergic reaction to the dye. Most reactions happen right away, but you could have a delayed reaction. After a CT scan that uses dye, watch for signs of a reaction. These signs include itching, rash, or sweating. If you start having these symptoms, call your healthcare provider right away. If your throat gets swollen or you have trouble breathing, call 911 for emergency medical care.

What are the benefits of this procedure?

A CT scan provides detailed pictures to:

  • Help your healthcare provider diagnose a problem.
  • Get important follow-up information after a treatment, such as surgery or chemotherapy.

What are the risks associated with this procedure?

When you have a CT scan, your body is exposed to some radiation. The amount of radiation depends on the size of the area being X-rayed. For example, a CT scan of the belly and pelvis requires much more radiation than a simple chest X-ray. Exposure to radiation can be dangerous if you are exposed to it often or in large amounts. However, a CT scan will normally be ordered only if it is needed for diagnosis or follow-up of your treatment.


If you are pregnant, you should not have a CT scan or other X-rays without first discussing the possible risks to your baby with your healthcare provider.


There is a small risk that you will have an allergic reaction to the dye. For example, there is a chance you will be allergic to the dye if you have a shellfish allergy. Even if you are not allergic to the dye, the dye may cause warm feelings, a flushed face, headache, or a salty taste in the mouth. Rarely, it can cause nausea and vomiting.


Be sure to tell your healthcare provider if you know you are allergic to any medicines or chemicals such as iodine.

When should I call my healthcare provider?

Call your provider right away if:

  • You have a worsening of the pain or other symptoms you had before the test.
  • You are having symptoms of an allergic reaction: itching, rash, or sweating. If your throat is swollen or you have trouble breathing, call 911.

Call your provider during office hours if:

  • You have questions about the procedure or its result.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.


HIA File diag5116.htm Release 13/2010

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