CT scan
This page tells you about CT scans. There is information about
CT scan (or CAT scan) stands for Computerised ( Axial) Tomography scan. This means a scan that takes a series of X-rays and uses a computer to put them together. The scan is is painless. The CT machine takes pictures of your body from different angles and gives 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.
Together these cross sections give a very accurate picture of where a tumour is and how big it is. They also show how close major body organs are to the area that needs to be treated or operated on.
A CT scanning machine is large and shaped rather like a doughnut. There is a couch that you lie on.
The couch can slide backwards and forwards through the hole of the doughnut. The pictures are taken as you move through the machine. Below is a CT scan of the pelvis marked for radiotherapy treatment.
When you arrive, you check in with the receptionist so the radiographers know you are there. Then you usually take a seat in the waiting room until someone calls you for your scan.
When you are called, you may first go to a cubicle to take off your outer clothing. 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. You must take off any jewellery in the area to be scanned because metal interferes with the machine.
When you are ready, the radiographer or helper will take you into the scanning room. You will probably have to lie down on the machine couch on your back. Sometimes the scan is done with you on your side or lying on your front. You need to lie as still as you can, but can breathe normally.
Once you are in the right position on the couch, the radiographer will leave the room. This is because there will be X-rays in the room and it would be dangerous for the staff to be exposed to these. They see patients having X-rays and CT scans all day, every day and if they stayed in the room, would be exposed to far more X-rays than any patient.
The radiographer will be able to see you on a TV screen and you can talk to each other through an intercom. The radiographer controls the position of the couch from outside. The couch can move automatically through the CT scanner so that the part of the body to be scanned is in the machine. The radiographer will tell you that they are about to start the scan and will remind you to keep as still as you can. When the scan is over, the radiographer will come back into the room and help you down from the couch.
Most scans take about half an hour. A lot of that time is to set up the scan, rather than actually taking it. Lying still for that long can be uncomfortable. If you are getting stiff and need to move, tell the radiographers through the intercom. During the actual scan, you have to try to keep as still as possible, and not cough or swallow, particularly if your head is being scanned. Mostly, you can breathe quietly but normally throughout the scan. For some scans, your radiographer may ask you to hold your breath at various times. If this is going to happen, they will tell you beforehand. You should be able to go home as soon as the scan is over.
Some people feel a bit claustrophobic ('closed in') when they are having a scan. If you think you are likely to feel this way, it is helpful to tell the radiographers before the day of your appointment.
If necessary, you can have a tablet or injection to calm you down before the scan. If you need a sedative, it needs to be organised in advance so do ring the department if you think you'll need one. If your radiographers know you are nervous, they will take extra care in making sure you are comfortable and that you understand what is going on. Keeping your eyes closed sometimes helps.
Some CT scans need special preparation beforehand. This is explained below for scans of different parts of the body. For some scans, you will have a drink or injection of 'contrast medium'. This is a dye that shows up body tissues more clearly on the scan. Before you have this, the nurse or radiographer will ask you about allergies or asthma as some people can be allergic to it. The injection may make you feel hot and flushed for a minute or two.
If you are having a CT scan of your abdomen, you may be asked
- Not to eat or drink after midnight the night before the scan
- To drink a liquid 'contrast medium' 24 hours before the scan
- To drink more of the liquid in the X-ray department
You may have the contrast medium by injection either instead of, or as well as, the drink. The contrast medium makes the digestive system (gut) show up more clearly in the scan. It does not have any side effects.
For some brain scans, you may be given an injection of the 'contrast medium' dye beforehand to make the scan clearer.
For some chest (thoracic) scans, you may be given an injection of the 'contrast medium' dye beforehand. This is to help show up the tissues in the area containing the cancer, for example blood vessels. It may help to show whether the cancer can be removed with surgery or not.
If you are having a CT scan of the pelvis, you may be asked
- Not to eat or drink after midnight the night before the scan
- To have an injection of 'contrast medium' just before the scan
Depending on the part of your pelvis being scanned, you may have an injection of a drug to slow down the normal movement of your bowel. This movement (called 'peristalsis') can distort the scan and make it more difficult to read.
Occasionally, for a rectal scan, you need to have an enema of the 'contrast medium' dye. This shows up on the X-ray and makes the outline of the bowel show up more on the scan. This 'rectal contrast' isn't used very often. It may make you constipated. Your first couple of bowel motions will be white, but there are no other side effects.
There is a very detailed scan of the bowel called a 'virtual colonoscopy'. If you are having one of these, you will be asked
- Not to eat or drink for 36 hours before the scan
- Take 2 doses of a strong laxative the day before the scan
If you are diabetic, your doctor may want you to come into hospital a day or two before the scan. It may not be sensible for you to avoid eating and drinking for 36 hours without medical supervision.
Just before the scan, you'll have two injections. One is the 'contrast medium' dye to show up the body tissues more clearly. The other is a drug to slow down the normal movement of your bowel which can make the scan less clear. You will also have a tube put into your back passage. The radiographers put air through this tube to inflate your bowel and make the scan clearer. This can cause wind from your back passage and some people find this very embarrassing. The staff are very used to doing this type of test though. They won't be embarrassed by it so you don't need to worry about that.
For virtual colonoscopy, you will have two scans - one on your back and one on your front.
A spiral CT scan is a newer type of CT scan, also known as a 'helical' CT scan. It is faster than a standard CT scan and gives a very detailed picture of your organs and tissues, including blood vessels. This can make it useful for picking up very small tumours. It's called a spiral scan because the X-ray beam rotates around you during the scan in a spiral shape. This gives the radiographers a continuous picture, with no possible gaps between the 'slices' of the scan.
You should not have a CT scan if you are pregnant as it could be dangerous for the baby. Other than this situation, a CT scan is not dangerous. It involves being exposed to some radiation and this is why doctors are reluctant to do any scans without good reason. But it isn't a large enough amount of radiation for you to have any ill effects. If you are having a scan to check out symptoms or for a known medical condition, it will give useful information to your doctors. The benefits of this outweigh any potential risk. Doctors like to keep the number of scans you have to a minimum because this also keeps your radiation exposure as low as possible. So, most doctors would not recommend CT scans routinely as part of a check up for a healthy person
Very, very rarely, someone has an allergic reaction to the contrast injection. The reaction most often starts with weakness, sweating and difficulty breathing. The doctors and radiographers will know what to do if you have this type of reaction and will treat you very quickly.
It can take time for test results to come through. How long will depend on why you are having the scan. Usually, the scan is examined by a specialist in radiology and a report is typed up. The report is then sent to your specialist, who will then gives you the results. If your GP has sent you for the test, the results will be sent directly to their surgery.
Understandably, waiting for results can make you anxious. It usually takes a couple of weeks for the results to come through. If your doctor needed the results urgently, it would have been noted on the scan request form and the results will be ready sooner than that. Try to remember to ask your doctor how long you should expect to wait for the results when you are first asked to go for the test. If it is not an emergency, and you have not heard a couple of weeks after your test, ring your doctor's secretary to check if they are back.
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