CT scans became widely available in the UK about 20 years ago. The initials CT stand for computerised tomography. CT-scanners produce a specialised type of x-ray which builds up a three-dimensional picture of the inside of the body. The scan is painless. It takes longer than an ordinary x-ray (about 30 minutes) and involves lying on a couch which moves through a short tunnel, which houses the scanner. Most people who have a CT-scan are given a drink or injection of dye to allow particular areas to be seen more clearly. For a few minutes this may make you feel hot all over.

MRI scans became widely available in Britain during the 1990s. The initials stand for magnetic resonance imaging. The test is similar to a CT-scan but uses magnetic fields rather than x-rays to build up a series of cross-sectional pictures of the body. During the test, which may take longer than a CT-scan, you will be asked to lie very still on a couch inside a metal cylinder. It can be slightly uncomfortable and some people find it claustrophobic. The scan is also very noisy but you may be given earplugs or headphones to wear. Once again drinks or an injection of dye may be used to show up particular parts of your body.

Both types of scanner use computers to produce the pictures of your body and it usually takes a day or two to get the results of the scans.

At the present time there are many more CT-scanners in the country than MRI scanners but the numbers of both types of scanner are increasing all the time.

CT and MRI scanners are used to help diagnose and assess many different medical conditions. In cancer they are of great help in showing the exact position of tumours and helping to see whether or not they have spread.

In diagnosing and assessing cancers the two sorts of scanner are complimentary: for some cancers CT-scans will give more accurate information whilst for others an MRI scan is better. So the choice of which sort of scan is used depends on which type of cancer is suspected, or being investigated, and your medical team will be able to decide which of the tests is needed. Sometimes both CT and MRI scans are used to get even more information.