Computed tomography, sometimes called a CT or CAT scan, is type of x-ray. It takes pictures from different angles and combines the images to create detailed slices of an organ, bone, blood vessel, or other tissue. The cross-sectional images can be viewed in 3-D, giving your healthcare provider an idea of the extent (size) of the damage or disease and exactly where it is located.
Positron emission tomography (PET) is another type of CT scan that uses radiotracers (radioactive materials) and a special camera to view your organs and tissues. It is sometimes called nuclear imaging. PET can help doctors find disease in its earliest stages because it shows changes at the cellular level.
CT scans are fast, painless, and accurate. A CT scan may be recommended to:
- Find tumors, infections or blood clots
- Examine fractures or internal injuries due to an accident or trauma
- Determine the location and size of bleeding in the brain or another organ
- Understand what may be causing headaches, weakness, or a change in personality
- Help surgeons navigate during a procedure
In some cases, contrast (dye) is put into the blood stream to highlight an area of concern, such as plaque (hardened fat) in an artery. A patient may also be asked to drink a special liquid containing contrast to show changes in the digestive tract (gut).
CT scans are generally not recommended for pregnant women. Be sure to tell your healthcare provider before the test if there is any chance at all that you may be pregnant. Other risks include:
- Radiation exposure. CT uses the same type of ionized radiation as a standard x-ray, however, more radiation is needed to create the more detailed images. While CT scans have not been shown to cause any long-term problems, there is always a slightly higher risk of getting cancer from repeated exposure to radiation. Children have a higher risk of radiation exposure. Talk with your healthcare provider about the level of radiation exposure with each test. In almost all cases, the benefits are greater than the risks.
- Allergic reaction to contrast. Most contrast materials contain iodine. Allergic reactions to iodine are rare, but possible. Tell your healthcare provider if you or your child have ever had a reaction to iodine.
The exam usually takes about 30 minutes.
- You will lay on an examination table that is attached to the scanner. A technician will help position your body. You may need straps or pillows to help your body stay in the correct position during the scan.
- If contrast is being used, it will be injected into a vein in your arm or the area to be examined (your spine, for example).
- The table moves slowly through the scanner. The scanner is shaped like a thick ring and is open on the other side. You may move through the scanner several times.
- You may be asked to hold your breath. This is to help your body stay still so that clear images can be taken.
Wear loose, comfortable clothing to the exam. You may be asked to wear a gown and to remove jewelry, piercings, eyeglasses, dentures, hearing aids hairpins, underwire bras, or anything that may affect the quality of the CT image.
If you are having a CT with contrast, you may be told not to eat or drink for a few hours before your test. If you have an allergy to contrast, you may need to have a steroid injection before the test to prevent a reaction.
The CT scans are reviewed by a radiologist – a doctor who specializes in reading imaging tests. A report will be sent to your healthcare provider detailing what, if anything, may be of concern.
It might take anywhere from 12 hours to 3 days to get your test results. Your doctor or nurse will usually call you with the results, or discuss them with you during a follow-up appointment. If the test was done because of an emergency, the results can be made available more quickly.