A CT scan uses X-rays to make a three-dimensional image of a cross-section (slice) of the inside of your body.
CT scans are usually carried out by a radiographer (a health professional trained to perform imaging procedures). It can be used to diagnose and monitor a number of different health conditions, such as suspected appendicitis or certain types of cancer. CT scans can also help to assist with other procedures or treatments. For example, if you’re having a biopsy (a small sample of tissue taken) to diagnose a disease, a CT scan may be used to help guide the needle to the right position.
A CT scanner is a large, ring-shaped machine with a hole in the centre. Inside the ring is an X-ray tube that produces a fan-shaped beam of X-rays. As you lie flat on the scanner table, the tube rotates around you and creates individual images of cross-sections of your body. A computer then joins the individual images together. This will often involve producing several sets of images taken in different directions and also some three-dimensional images. The images from a CT scan appear in different shades of grey.
CT scans are routinely done as an outpatient procedure. This means you will have the scan and go home the same day.
Your radiographer will discuss with you what will happen before, during and after your scan. This is your opportunity to understand what will happen. You can help yourself by preparing questions to ask about the risks, benefits and any alternatives to the procedure. This will help you to be informed, so you can give your consent for the procedure to go ahead.
You must tell your radiographer if you have:
Also, if you have claustrophobia (an extreme or irrational fear of confined places), tell your radiographer before the scan is started.
You may be asked not to eat or drink anything for a few hours beforehand, particularly if you’re having a CT scan of your abdomen (tummy).
A dye called contrast medium may be used to make your tissues show up more clearly on the images produced by the scan. Depending on which area of your body needs to be scanned, you may be asked to swallow the contrast medium. Otherwise it may be injected into a vein in your hand or arm, or inserted into your rectum (back passage). If you’re given an injection of contrast medium, this usually gives a warm sensation which passes shortly. Some people also get a feeling of needing to pass urine but this also goes away quickly.
A CT scan usually takes about 20 minutes.
Depending on which part of your body needs to be scanned, you may be asked to remove your clothing and put on a hospital gown. There will usually be a private area where you can do this. You may also be asked to remove any jewellery, glasses, contact lenses, dentures, hair clips and hearing aids.
You will be asked to lie on the scanner table, which slides into or out of the CT scanner ring. Your radiographer will position the table so that the part of your body needing to be scanned is in the centre of the scanner. You may also be asked to hold your breath or not to swallow at certain points during the scan. For the rest of the time, it's important to lie very still. The CT scanner will usually make some whirring noises when you’re inside.
Your radiographer will operate the scanner from a control room behind a window. He or she will be able to see, hear and speak to you at all times during the procedure.
Radiographer operating the CT scanner
When the scan is complete, the scanner table will move back out of the scanner ring and you will be helped down. You will usually be able to go home when you feel ready.
Your results will be reviewed by a radiologist (a doctor who specialises in using imaging methods to diagnose medical conditions). Usually, a report will be sent out by the radiologist to your GP or the doctor who referred you for the test; your scan may also be sent. This can take several days. Before you go home, ask your radiographer when you can expect to get your results.
As with every procedure, there are some risks associated with having a CT scan. We have not included the chance of these happening as they are specific to you and differ for every person.
You're exposed to natural background radiation in the atmosphere all the time. Different radiology procedures expose you to different doses of radiation. For example, the amount of radiation you receive from a CT scan is more than other types of radiology procedures, such as a plain X-ray. However, doctors are trained to keep your exposure to a minimum. Ask your radiographer to explain how these risks apply to you.
Complications are when problems occur during or after the procedure. Most people aren't affected.
It's possible you may have an allergic reaction to the contrast medium, but this is rare. If you have any itching or difficulty breathing, tell your radiographer immediately.
If you’re pregnant
If you’re pregnant, you will usually be advised not to have a CT scan as there is a risk that the radiation could harm your unborn baby. If you‘re pregnant, or think you might be, let your doctor or radiographer know.
Reviewed by Kuljeet Battoo, Bupa Health Information Team, September 2013.
For answers to frequently asked questions on this topic, see FAQs.
For sources and links to further information, see Resources.
This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.