CT (or CAT) scan stands for computerised (axial) tomography scan. The scan uses X-rays and a computer to create detailed images of the inside of your body.
A CT scanner is a large ring-shaped machine. The X-ray scanner inside the ring rotates in small movements around your body as you lie on a bed that moves backwards and forwards through the ring. As you move through the machine, the scanner uses a series of X-ray beams to scan parts of your body and build up detailed images.
The images produced by a CT scan are called tomograms. They are more detailed than standard X-rays, which use a single beam of radiation, and can give views of structures inside the body including internal organs, blood vessels, bones and tumours.
A CT scan can be used to diagnose or monitor many different health conditions, including cancer and bone disease. It is often used to provide views of your body before another procedure takes place, such as a biopsy or radiotherapy treatment.
A CT scan is painless and usually takes between 10 and 30 minutes, depending on which part of your body is being scanned.
Is it safe?
You will be exposed to X-ray radiation during a CT scan. The amount of radiation you are exposed to is safe and is not enough to cause any harm.
However, CT scans are not recommended for pregnant women because of the risk to the unborn baby. Children are more at risk than adults from a build-up of radiation doses and should only have a CT scan if it is justified by a serious condition that puts them at a higher risk.
If you are advised to have a CT scan to diagnose a condition or to check symptoms of a known medical condition, the benefits of having the scan will outweigh any potential risk.
Continue to next section: How a CT scan is performed