CT scan (computed tomography)

Published by Bupa's Health Information Team, June 2011.

This factsheet is for people who are having a computed tomography (CT) scan, or who would like information about it.

A CT scan uses X-rays to make a three-dimensional image of the body or part of the body.

You will meet the radiographer carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.

About CT scan

A CT scan is a test that produces a three-dimensional image of a part of the inside of your body. It can be used to diagnose and monitor a number of different health conditions, including cancer. CT scans are also helpful to assist with other procedures or treatments, for example if you have a biopsy (small sample of tissue) taken.

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 that are cross-sections (slices) of your body.

The images from a CT scan are black, white and grey – just like X-rays. A computer then joins the individual images together to produce three-dimensional views.

What are the alternatives to a CT scan?

Alternative imaging procedures include ultrasound and MRI scans. Your doctor will let you know which procedure is most suitable for you.

Preparing for a CT scan

Your radiographer (a health professional trained to perform imaging procedures) will explain how to prepare for your scan.

CT scans are routinely done as an outpatient procedure. This means you will have the scan and go home the same day.

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 swallow the contrast medium as a liquid, have it injected into a vein in your hand or arm, or have it inserted into your rectum (back passage). If you're given an injection of contrast medium, this usually gives a warm sensation that passes after a short time. Some people also get a feeling of needing to pass urine but this also goes away quickly.

Your radiographer will discuss with you what will happen before, during and after your scan. This is your opportunity to understand what will happen, and 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 asthma, diabetes or kidney problems and let him or her know if you have any allergies – particularly to contrast medium. Also, if you have claustrophobia (an extreme or irrational fear of confined places), it's a good idea to mention this to your doctor or radiographer before the scan is started.

What happens during a CT scan

A CT scan usually takes about 20 to 30 minutes.

Depending on which part of your body needs to be scanned, you may be asked to take off your clothes and put on a hospital gown. There will 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.

A radiographer preparing a man for a CT scan, with the man lying on the table.

CT scan

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.

A radiographer operating the scanner from a control room behind a window.

Radiographer operating the CT scanner

What to expect afterwards

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 scan will then be sent to your doctor. Usually, a report will also be sent out by a radiologist (a doctor who specialises in using imaging methods to diagnose medical conditions). This can take several days. Before you go home, ask your radiographer when you can expect to get your results.

What are the risks?

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. During the scan you will be exposed to X-ray radiation. In excessive amounts this can slightly increase your risk of getting cancer. 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 to 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.


For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • 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.

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  • Publication date: June 2011

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