CT: Computed Tomography

What is CT?

Computed Tomography (CT) uses an X-ray which rotates around the body to produce 3D images of the inside of the body.

During the scan you will lie on a couch which moves quietly into the CT.

Some CT scans are done with a liquid (contrast) that shows up on the scan. A small needle (a small tube or cannula) is put into the arms so the contrast can be injected during the scan.

You may also be asked to drink water or mixture of water and contrast before your examination which will help your doctor to see the part of the body they are interested in more clearly.

What information is obtained?

CT gives us a lot of information and this information means that images can be displayed in a lot of different ways.

However, CT is associated with a higher dose than, for example, normal X-rays. The dose will depend on the part of the body being scanned, and how many parts are being scanned.

What do I need to know?

This video tells you what to expect if you having a CT and gives you information about the risks associated with it.

Take away points:

  • CT scans are short and not noisy.

  • They are not like a tunnel, you will be able to see out of them.

  • The radiographer will leave the room but can still see and hear you.

  • CTs lead to a small increase in the lifetime risk of cancer of about 1 in 1000. Your natural risk is 1 in 2.

  • You should inform the Radiographer if you could be pregnant.

  • If you have the contrast liquid (also known as dye) you may get a strange taste in your mouth and a warm feeling in your body for a few seconds. The contrast can also make you feel sick.

  • Tell the person doing your scan if you have had a reaction to contrast in the past.

  • Tell the person doing your scan if you have any allergies or asthma, or if you have any problems with your kidneys.

  • If you would like to find out more about the risks of CTs please follow this link.

Patient shielding

In the past you may have been given a lead apron or small shields for a certain body part during an X-ray. Recent science shows that this is usually not necessary due to improvements in technology and scientific knowledge.

Therefore, you may notice that you are no longer offered shielding where you previously were. If you would like more information on why this change has happened you can find it in the document "Guidance on using contact shielding on patients for diagnostic radiology applications" (BIR).


  • CT will only be used if a healthcare professional can show that the benefit to you is greater than the risk (justified).

  • X-rays used by CT do not hurt.

  • The equipment will be maintained to reduce the dose to keep the dose and risk to you as low as possible.

  • The individual carrying out the imaging will be trained to keep the dose and risk to you as low as possible.

  • If you have any more questions please ask a healthcare professional.

If you'd like to find out more about the risks of CT, there is more information within the 'Radiation Risk' section.