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CT scan

A CT scan is a test that uses x-rays and a computer to create detailed pictures of the inside of your body. It takes pictures from different angles. The computer puts them together to make a 3 dimensional (3D) image.  

CT (or CAT) stands for computed (axial) tomography.

Photo of a CT scanner

You usually have a CT scan in the x-ray (radiology) department as an outpatient. A radiographer operates the scanner. The whole appointment can take up to an hour and a half depending on which part of your body they are scanning. 

Why you might have a CT scan

You usually have a CT scan of the brain to help diagnose a brain tumour. It can help to find where the tumour is and whether it has spread.

You may also have a CT scan of your tummy (abdomen) and chest to check whether you have cancer anywhere else in your body. This is because in adults, cancer that has spread to the brain from another part of the body (secondary brain cancer) is much more common than cancer that started in the brain (primary brain tumour). 

Preparing for a CT scan

Some CT scans need special preparation beforehand.

For most scans, you have a drink or an injection of contrast medium, or both. This is a dye that shows up body tissues more clearly on the scan. You have the injection through a small thin tube (cannula) in your arm. The tube is left in place until after your scan, in case you have any problems after having the injection.

A couple of hours before your scan you might need to stop eating and drinking. Talk to your doctor if not eating is a problem for you for example, if you have diabetes.

What happens

When you arrive

The radiographer might ask you to change into a hospital gown. You should remove jewellery and other metal objects, such as hair clips around the area being scanned. Metal interferes with the images produced by the scanner.

In the scanning room

When you’re ready, the radiographer or assistant takes you into the scanning room. A CT scanning machine is large and shaped like a doughnut.

You might have an injection of contrast medium through a small tube (cannula) in your arm. You may:

  • feel hot and flushed for a minute or two
  • have a metallic taste in your mouth
  • feel like you’re passing urine but you aren’t – this feeling is common and passes quickly

Tell the radiographer if you feel anxious or claustrophobic about having a scan. 

Having the CT scan

You usually lie down on the machine couch on your back. Once you’re in the right position, the radiographer leaves the room. They can see you on a TV screen or through a window from the control room. You can talk to each other through an intercom.

The couch slowly slides backwards and forwards through the hole of the scanner. The machine takes pictures as you move through it. 

The scan is painless but can be uncomfortable because you have to stay still. Tell your radiographers if you’re getting stiff and need to move.

During the scan

You’ll hear a whirring noise from the scanner.

The radiographer might ask you to hold your breath at times.

When the scan is over, the radiographer comes back into the room and lowers the couch so you can get up.

The 2-minute video shows what happens when you have a CT scan.

After your CT scan

You stay in the department for about 15 to 30 minutes if you had an injection of the dye. This is in case it makes you feel unwell, which is rare.

The radiographer removes the cannula from your arm before you go home.

You should be able to go home, back to work or the ward soon afterwards. You can eat and drink normally.  

Possible risks

A CT scan is a safe test for most people but like all medical tests it has some possible risks. Your doctor and radiographer make sure the benefits of having the test outweigh these risks.

Allergic reaction

Rarely, people have an allergic reaction to the contrast medium. This most often starts with weakness, sweating and difficulty breathing. Tell your radiographer immediately if you feel unwell.

Bruising and swelling

You might get a small bruise around the area where they put the needle in.

There's a risk that the contrast medium will leak outside the vein. This can cause swelling and pain in your hand or arm but it’s rare.

Kidney problems

There is a small risk that the contrast medium can affect your kidneys. Your radiographer checks your most recent blood test results before your scan to make sure your kidneys are working well. 

Radiation

Exposure to radiation during a CT scan can slightly increase your risk of developing cancer in the future. Talk to your doctor if this worries you.

Pregnancy

Pregnant women should only have CT scans in emergencies. Contact the department as soon as you can before the scan if you are pregnant or think that you might be.

Getting your results

You should get your results within 1 or 2 weeks. 

Waiting for results can make you anxious. Ask your doctor or nurse how long it will take to get them. Contact the doctor who arranged the test if you haven’t heard anything after a couple of weeks.

You might have contact details for a specialist nurse who you can contact for information if you need to. It may help to talk to a close friend or relative about how you feel.

For information and support, you can contact the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday.

More information

We have more information on tests, treatment and support if you have been diagnosed with a brain or spinal cord tumour.

Last reviewed: 
14 Mar 2019
  • Oxford handbook of clinical medicine (10th edition)
    M Longmore and others
    Oxford University Press, 2017

  • The Royal Marsden Manual of Clinical Nursing Procedures (9th Edition)
    L Dougherty and S Lister (Editors)
    Wiley Blackwell, 2015

  • Recommendations for cross-sectional imaging in cancer management (2nd Edition)
    The Royal College of Radiologists, 2014

  • Brain Tumor Imaging
    K Brindle and others
    Journal of Clinical Oncology, 2017. Vol 35, Number 21, Pages 2432-2438

  • Brain tumours (primary) and brain metastases in adults
    The National Institute for Health and Care Excellence (NICE), July 2018

  • Overview of the clinical features and diagnosis of brain tumors in adults
    E Wong and J Wu 
    UpToDate, Last accessed March 2019

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