A CT (computed tomography) scan is a medical procedure that takes pictures of the inside of your body. It used to be known as a CAT scan.
It helps diagnose medical conditions, for example when someone has internal injuries in an accident, and helps doctors plan medical treatment.
What is a CT scan?
A CT scan is a type of x-ray which creates three-dimensional images of your body. The machine moves in a circular motion around you and takes x-rays of very thin slices of your body. This allows very detailed images of your body to be developed.
When is a CT scan used?
A CT scan may be used:
- to diagnose and monitor many different conditions such as tumours or infections
- to look for injuries after a serious accident
- to help plan treatment such as surgery or radiotherapy
- to diagnose abnormal anatomy
- to help guide doctors doing a biopsy
Any part of your body can be scanned, and common areas include the head, chest, abdomen and pelvis. A CT scan can also be used to look at bones, blood vessels, soft tissue (for example muscle) and organs (for example the brain).
Possible risks from a CT scan
Allergic reaction to contrast dye
Some CT scans require an injection of a special dye called contrast material to help show certain structures. There is a small risk of allergic reaction to this dye, which commonly results in a rash or itchiness. If you know you have an allergy to contrast material, tell your doctor.
Modern CT scanners use x-rays, a type of radiation that has been linked to cancer. While CT scans produce more radiation than other types of imaging, the risks of this radiation must be balanced against the need for the CT scan. To minimise risks, CT scans should only be used where necessary.
People at increased risk include younger people and people who have had repeat scans. CT scans are avoided in these people unless medically necessary.
Read more about ionising radiation and health.
If you are pregnant, or think you might be pregnant, talk to your doctor. CT scans are best avoided in pregnancy, as there is a risk that the radiation could harm the unborn baby.
Read more about risks of CT scans.
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Last reviewed: January 2019