What is a CT scan?

A computerised tomography (CT) scan uses X-rays and a computer to create detailed cross-sectional images of the inside of the body.   CT scans are sometimes referred to as CAT scans or computed tomography scans.

CT scans can produce detailed images of many structures inside the body, including the internal organs, blood vessels and bones.

They can be used to:

  • diagnose conditions – including damage to bones, injuries to internal organs, problems with blood flow, strokes and cancer
  • guide further tests or treatments – for example, CT scans can help to determine the location, size and shape of a tumour before having radiotherapy, or allow a doctor to take a needle biopsy (where a small tissue sample is removed using a needle) or drain an abscess
  • monitor conditions – including checking the size of tumours during and after cancer treatment

Preparing for a CT scan

Your appointment letter will mention anything you need to do to prepare for your scan.

You may be advised to avoid eating anything for several hours before your appointment, to help ensure that clear images are taken.

You should contact the hospital after receiving your appointment letter if you have any allergies or kidney problems, or if you’re taking medication for diabetes, because special arrangements may need to be made.

You should also let the hospital know if you’re pregnant. CT scans aren’t usually recommended for pregnant women unless it’s an emergency, as there’s a small chance the X-rays could harm your baby.

It’s a good idea to wear loose comfortable clothes, as you may be able to wear these during the scan. Try to avoid wearing jewellery and clothes containing metal (such as zips), as these will need to be removed.

Before having the scan, you may be given a special dye called a contrast to help improve the quality of the images. This may be swallowed in the form of a drink, passed into your bottom (enema), or injected into a blood vessel.

What happens during the CT scan?

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 that rotates around a small section of your body as you pass through it. Unlike a magnetic resonance imaging (MRI) scan, the scanner doesn’t surround your whole body at once, so you shouldn’t feel claustrophobic.

The radiographer will operate the scanner from the next room. While the scan is taking place, you’ll be able to hear and speak to them through an intercom.

While each scan is taken, you’ll need to lie very still and breathe normally. This ensures that the scan images aren’t blurred. You may be asked to breathe in, breathe out, or hold your breath at certain points.

The scan will usually take around 10-20 minutes.

What happens afterwards

You shouldn’t experience any after effects from a CT scan and can usually go home soon afterwards. You can eat and drink, go to work and drive as normal.

If a contrast was used, you may be advised to wait in the hospital for up to an hour to make sure you don’t have a reaction to it (see below). The contrast is normally completely harmless and will pass out of your body in your urine.

Your scan results won’t usually be available immediately. A computer will need to process the information from your scan, which will then be analysed by a radiologist (a specialist in interpreting images of the body).

Results

The images will be examined after your visit by a Consultant Radiologist who will send a written report on the findings to your GP or consultant.

Please tell a member of the team if you have had a similar scan recently or if you are a woman who is or might be pregnant.