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.
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 it
A CT scan can show abnormal swellings in the lining of your lungs (pleura) or abdomen (peritoneum).
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, your radiographer or an assistant takes you into the scanning room. A CT scanning machine is large and shaped like a doughnut.
You might have an injection of a type of dye called a 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 your 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, your radiographer leaves the room to protect them from the radiation. 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 radiographer if you’re getting stiff and need to move.
During the scan
You’ll hear a whirring noise from the scanner.
Your radiographer might ask you to hold your breath at times.
When the scan is over, your radiographer comes back into the room and lowers the couch so you can get up.
This 2 minute video shows what happens when you have a CT scan.
Voiceover: A CT scan helps your doctor make a diagnosis, decide about what treatment you need or find out if your treatment is working.
This type of scan takes a series of x-rays and uses a computer to put them together.
Before your scan you may need to drink either half a litre of water or a type of dye called a contrast medium. This helps to make the scan clearer.
Before most scans you have a small tube put into your vein, which connects to a drip containing the dye. Again, this helps to show up the inside of your body more clearly on the scan.
During the scan the bed moves in and out of the scanner. You may find it a bit noisy.
As the drip goes in you’ll probably get a metallic taste in your mouth, feel warm and you might think you are passing urine, you’re not. These feelings pass quickly.
The radiographer controls the scan from a separate room. The CT machine takes pictures of your body from different angles and builds up a series of cross sections.
This creates a very detailed picture of the part of your body being scanned. Most scans take just a few minutes. The whole thing takes about 90 minutes and you usually get the results within a couple of weeks.
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.
Your 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.
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.
If the CT scan shows an abnormal area in your chest your doctor may suggest you have a sample of tissue taken (a biospy). They may do this using another CT scan.
CT guided biopsy
You have a local anaesthetic to numb the area where they are going to put the biopsy needle. Then using a CT to see exactly where the tumour is, your doctor puts a fine needle through the skin and into the tumour. Then they take a small piece of tissue out with the needle.
This should not be painful because of the local anaesthetic. But you will feel pressure when the needle goes in.
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.
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.
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.
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.
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.