You might have a CT scan to find out the size of the cancer in your anus and whether it has spread to other parts of your body.
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
Why you might have a CT scan
You might have a CT scan of your chest, tummy (abdomen) or pelvis (the area between your hip bones). This is to look at the cancer in the anus and see if it has spread to other parts of your body.
Preparing for your CT scan
CT scan of the chest
You might have an injection of the contrast medium during the scan. This is to help show up the tissues close to the area containing cancer. For example, if your doctor wants to know if the cancer is affecting your blood vessels. It may help to show whether cancer can be removed with surgery or not.
CT scan of the abdomen
If you are having a CT scan of your abdomen, you might need to:
- drink a liquid contrast medium some time before the scan
- drink more of the liquid contrast or water in the x-ray department
- stop eating or drinking after midnight the night before the scan (this is for a CT scan of the inside of the large bowel, called CT colonography)
You usually have the contrast medium by injection and also as a drink. This helps to show up the gut (
Pelvic CT scan
If you are having a CT scan of the pelvis, you might be asked:
- not to eat or drink for some time before the scan
- to have an injection of contrast medium
Occasionally, for a rectal scan, you need to have an enema of contrast medium. This shows up on the x-ray and makes the outline of the bowel show up more on the scan. It might make you constipated. Your first couple of bowel motions will be white, but there are no other side effects.
When you arrive you usually fill out a checklist or questionnaire with the radiographer. They also explain about what to expect during the CT scan.
Once you're happy to proceed they usually give you a hospital gown to change into. It’s a good idea to take a dressing gown with you if you have one. You can then wear this on top of the hospital gown whilst waiting for your scan.
Before the scan you remove any jewellery and other metal objects, bra, hair clips around the area being scanned. Metal interferes with the images produced by the scanner.
When it’s time, your radiographer or an assistant takes you into the scanning room.
In the scanning room
A CT scanning machine is large and shaped like a doughnut.
You might have an injection of contrast medium through the cannula. 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. 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 it 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.
The scan usually lasts between 20 and 30 minutes.
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.
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.
Some of the possible risks include:
An allergic reaction
Rarely, people have an allergic reaction to the dye (contrast medium). This most often starts with weakness, sweating and difficulty breathing. Your radiographer will ask if you have any allergies before you have the contrast medium. Tell them immediately if you feel unwell after having it.
Bruising and swelling
You might get a small bruise around the area where they put the needle in for the cannula.
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. This is to make sure your kidneys are working well. You may be able to have the scan without contrast medium if you have kidney problems.
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.
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. You may want them to go with you to get the results for support.