What is a CT scan?
A CT (computed tomography) scan is a type of x-ray that creates 3-dimensional images of your body, including bones, organs, tissues and tumours. The machine moves in a circular motion around you and takes x-rays of very thin slices of your body to create a cross-sectional image.
CT scans provide different views and far greater detail than a 2-dimensional x-ray. They may be used instead of an x-ray when your doctor needs to see soft tissues in your body, which don’t always show up on x-rays.
It helps diagnose medical conditions, for example when someone has internal injuries in an accident, and helps doctors plan medical treatment.
CT scans provide different information to an ultrasound, which uses sound waves to create real-time images of the inside of the body.
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).
How do I prepare for a CT scan?
You will receive instructions from the hospital or radiology practice before your appointment.
Many types of CT scans require an injection of a special dye called contrast material to help show blood vessels and some organs.
If you need contrast material for the CT scan, most hospital departments or radiology practices will ask you to fast (not eat or drink) before your appointment. You will receive instructions about fasting before your appointment.
What happens during a CT scan?
CT scans are tailored for each person, so all CT scans are slightly different.
Before the scan, you may be injected with contrast medium to make the pictures clearer.
During the scan, you'll usually lie on your back on a flat bed that passes into the CT scanner. The scanner consists of a ring, like a doughnut, that rotates around a small section of your body as you pass through it.
You'll be able to hear and speak to the radiographer in the next room through an intercom.
While each scan is taken, you'll need to lie very still and breathe normally so that the images are clear. You may be asked to breathe in, breathe out, or hold your breath at certain points.
The scan will usually take around 10 to 20 minutes. If you have an injection of contrast material, the sensations of warmth and the strange taste usually experienced should go away within a few minutes.
You can usually go home soon after the scan.
What are the possible risks of a CT scan?
Allergic reaction to contrast dye
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 2021