A Computerised Tomography (CT) scanner uses x-rays to produce images of various parts of the body. The images are produced from a block of data which the scanner acquires in one breath hold. These are turned into cross sectional images, like the slices of a loaf of bread. When the image slices are reassembled by computer, the result is a very detailed, multidimensional view of the body's interior.
CT scans are investigations that can be used to help to make a diagnosis or assess the effects of treatment. Your doctor will recommend a CT scan based on the type of cancer you have and the information needed to plan your treatment.
CT scanners use x-rays at the lowest practical radiation dose. The benefits of having a CT scan and the information obtained from the scan compared to the risk of exposure to radiation will be weighed up by your doctor before deciding to send you for the scan. If you have any queries about this, please speak to your doctor.
CT scans are not suitable for pregnant women. Please contact the CT department before your scan if you think there is any possibility you may be pregnant.
What will happen when I have my scan?
You will be given instructions on how to prepare for your CT scan.
- For all scans you must not eat or drink anything for two hours before your appointment time. It is important that your stomach is empty before the scan
- For scans of the abdomen and/or pelvic area you will be asked to drink up to a litre of fluid before the scan. This will help to identify your stomach and bowel clearly on the scans
- For some female patients having pelvic scans, a tampon may be inserted into the vagina.
You may be asked to undress and put on a hospital gown. For some scans, you may be able to wear your own clothes as long as they have no metal on them. You will also be asked to remove jewellery as metal can interfere with the scan and cause streaking on the images.
The scan itself will take between 10 to 15 minutes, depending on the number of pictures taken and the complexity of the scan. Generally you should expect to be in the department for about one to two hours.
The scanner looks like a large doughnut. You will be asked to lie on a cushioned table, which will move slowly through the scanner to allow pictures to be taken at different angles. The machine makes a noise while working.
During the scan an injection of fluid/dye (contrast medium) is often given into a vein in your arm or hand. This dye contains iodine, it is not radioactive, but shows up as white areas on the scans, helping the radiologist to tell the difference between blood vessels and other structures. You will be asked about allergies and your tablets to assess your suitability to have the injection and minimise interactions with other medicines.
For some scans you may be asked to hold your breath or to stop swallowing for short periods. A member of the scanning team will give you instructions about your breathing and let you know what is happening at each stage of the scan. Most of the time you can see out of either one side or the other of the scanner and therefore it is much less of a problem for people who feel claustrophobic. If you are worried about this, please speak to the radiographer before you come for your scan.
During the scan, the radiographer will be able to see you from the control room and you can talk to each other through an intercom.
What happens afterwards?
As soon as the scan is completed, you can get dressed. We recommend that you wait an hour after your injection to make sure that you are feeling well before you leave the department. You may go to the toilet and you can eat and drink normally. It is safe for you to drive home after the hour has passed.
There are no side effects to having a CT scan. Very occasionally, someone will have an allergic reaction to the injection of contrast medium. Staff working in the CT department are trained to manage this situation if it arises.
Whilst the radiographer can reassure you that the appropriate images have been obtained, we will not be able to give you any idea of the results at that time. The scans must be carefully analysed and interpreted by a radiologist, who will prepare a report and send it to your own doctor. Your doctor will tell you the results and discuss them with you.