Information for patients > Services > CT Scan
CT scanning
Information for patients
It is perfectly understandable to be apprehensive when you arrive for an investigation, but staff at all our sites are kind, friendly, informative and helpful and will help you to feel relaxed and calm. The information below should give you a reasonable idea about how to prepare for your particular type of investigation.
Frequently Asked Questions(FAQs) - CT Scan
What is a CT scanner used for?
How do I prepare for a CT scan?
What do I need to do immediately before a CT scan?
What happens during a CT scan?
What if I feel claustrophic during a CT scan?
A CT scan (or CAT scan as it is sometimes called) stands for a Computerised (Axial) Tomography scan. This just means a scan that takes pictures from all around your body and uses a computer to generate 3-dimensional images.
A CT scanner is a large machine, shaped rather like a doughnut. A CT scanner uses X-rays and, like an X-ray, it is painless. You lie on a couch that slides backwards and forwards through the hole of the doughnut. The CT machine takes a lot of pictures of your body from different angles as you move through the machine, and feeds the pictures into a computer. The computer puts them together to give a series of cross sections or 'slices' through the part of the body being scanned. A very detailed picture of the inside of the body can be built up in this way.
What is a CT scanner used for?
CT scanning can be used to image all parts of the body and to diagnose accurately a very wide range of conditions. CT may also be used to screen for coronary heart disease and some types of cancer (eg lung and bowel).
How do I prepare for a CT scan?
Some CT scans need special preparation beforehand, and this will be explained when you receive your appointment. You may be asked not to eat or drink before the scan. If you are having a CT colonography (virtual colonoscopy) study, you will be asked to take laxatives to clear your colon of faeces.
What do I need to do immediately before a CT scan?
You may have to strip down to your underwear and put on a hospital gown. If you are just having a CT of your head, you may not be asked to undress. Because metal interferes with the machine, ensure you take off any jewellery in the area to be scanned.
What happens during a CT scan?
The radiographer will take you into the scanning room. You will probably have to lie down on the scanner table on your back. Sometimes the scan is done with you on your side or lying on your front. It will be necessary for you to lie still.
For some scans, you will have an injection of a contrast agent, which will show up body tissues more clearly on the scan. Before you have this, the radiographer will ask you if you have a history of diabetes, asthma, kidney disease, thyroid conditions or allergies as people with these conditions may sometimes develop adverse reactions to the contrast. If you do have any of these conditions, it is best to let us know before your scan. The injection may make you feel hot and flushed for a minute or two, but the risk of serious allergic reaction is very small and the radiology staff are fully trained in dealing with any reaction.
Once you are in the right position on the table, the radiographer will leave the room. This is because there will be X-rays in the room, which would be dangerous to staff if they consistently stayed in the room with every patient.
The radiographer will be able to see you on a TV screen and you will be able to talk to each other through an intercom. The radiographer will control the position of the table from outside. The table moves automatically through the CT scanner, enabling the scanner to take pictures of the part of the body being imaged. You may be asked to hold your breath for a short period. When the scan is over, the radiographer will come back into the room and help you down from the table.
How long will a CT scan take?
Most scans take about 15 minutes. A lot of that is for setting up the scan, rather than actually performing it. You should be able to go home as soon as the scan is over.
What if I feel claustrophic during a CT scan?
Very few patients find a CT scan claustrophobic, as the scanner is less confining than an MRI scanner. However, if you think you are likely to feel this way, tell your GP before the day of your appointment and he can arrange for you to have a sedative to calm you down before the scan. If the radiographers know you are nervous, they will take extra care making sure you are comfortable and that you understand what is going on. Keeping your eyes closed sometimes helps.
CT scans are not dangerous in the short term, but do involve exposure to ionising radiation. This theoretically may increase your risk of developing cancer in later life, but this increase in risk is very small. This is why a CT scan will not be recommended by your doctor unless its benefits outweigh any potential risk. Doctors like to keep the number of scans you have to a minimum because this also keeps your radiation exposure down to a minimum.
Like any test involving radiation, you should not have a CT scan if you are pregnant unless absolutely essential, as it could be harmful for the baby.
Very, very rarely, someone has an allergic reaction to the contrast injection, which can be serious. If you do have this type of reaction, the doctors and radiographers will know what to do to treat it.
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