What is a CT scan?
A CT scan, also called computed tomography or CAT scan, is a special type of X-ray test. X-rays are taken from different angles and a computer puts the X-ray pictures together to create detailed views of the body. CT scans can show bone, muscle, fat, lymph nodes, organs, and blood vessels in detail.
When is it used?
CT scans are used when your healthcare provider needs more information than regular X-rays can show. For example, a CT scan may be used to:
- Show more details of a specific area of your body
- Help your healthcare provider guide a needle or catheter into the correct place in the body for a test or treatment
- Check for swelling or bleeding in the brain after a head injury
How do I prepare for this scan?
- For some CT scans no special preparation is needed. For others you may have special directions about what you should eat and drink before the test. Follow any instructions your healthcare provider may give you.
- You may or may not need to take your regular medicines the day of the procedure. For some types of CT scans, some medicines (like aspirin) may increase your risk of bleeding during or after the procedure. Tell your provider about all medicines and supplements that you take. Ask your provider if you need to avoid taking any medicine or supplements before the procedure.
- Tell your provider if you have had any kidney problems or reactions to foods or chemicals, such as X-ray contrast dye. Contrast dye is used for some CT scans.
- Wear comfortable clothing that has no metal zippers, buttons, or hooks. Leave your watch and jewelry at home.
- Tell your provider if you are or think you may be pregnant.
- Tell your provider if you are afraid of enclosed spaces. Your provider may prescribe medicine to help you relax during the scan.
- Ask any questions you have before the procedure. You should understand what your healthcare provider is going to do. You have the right to make decisions about your healthcare and to give permission for any tests or procedures.
What happens during the scan?
CT scans can be done in a hospital, an imaging center, or mobile unit.
You will lie down on a moving table that will slide into the scanner. The CT scanner is a large machine with a tunnel in the center. Inside the scanner, many X-ray beams are passed very quickly through your body at different angles. You will need to stay still during the scan so that the pictures will not be blurry. Images of your body will be seen on a computer screen and prepared for your healthcare provider to examine later.
For some scans, contrast dye may be needed to help show the part of the body being scanned. Contrast dye may be given in different ways. It may be:
- Injected into a vein
- Given as a chalky liquid that you drink
- Given into your rectum as an enema
The dye may make you feel warm. Your face may get flushed and you may get a headache or have a salty taste in your mouth. In rare cases, the dye can cause nausea and vomiting.
Depending on what area is being scanned, and whether or not a contrast dye is used, scans may last 15 to 30 minutes or longer. They are painless, but you may get uncomfortable if the scan takes more than a few minutes. Because of the small, enclosed space, some people get anxious. If you start feeling panicky or are having other problems, the scan may be stopped. Your healthcare provider may recommend giving you medicine to help you relax before and during the scan.
What happens after the scan?
Usually, you can go home soon after the test. If you were given medicine to help you relax, you will be watched carefully until you are fully awake and alert. This may take 15 minutes to 2 hours.
If you were given dye for the scan, drinking lots of fluids after the scan helps your body get rid of the dye.
Ask your healthcare provider:
- How and when you will hear the test results
- What symptoms or problems you should watch for and what to do if you have them
What are the risks of this scan?
Every procedure or treatment has risks. Some possible risks of this scan include:
- The radiation you get from a CT scan may cause a small increase in your lifetime risk of developing cancer.
- In rare cases you may have an allergic reaction to medicines used during the procedure.
- If you are pregnant, there is a risk the X-rays will hurt the baby.
Ask your healthcare provider how these risks apply to you. Be sure to discuss any other questions or concerns that you may have.
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This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
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