COMPUTED TOMOGRAPHY (CT)
CT is a way of using X-rays to take pictures or images in very fine slices through the part of the body that the doctor has asked to be investigated. One way to think of it is of taking slices through a loaf of bread. When you take slices from your loaf of bread, you are able to see much more detail about the structures that make up the loaf. The slices that are taken are often less than 1 millimetre thick. Once the radiographer has taken the scan, these very thin slices can be put all together to reconstruct the loaf (or in this case your body). Once they are put back together the radiographer can cut it into the slices that will help the radiologist to see the parts of the body that are of interest. This will often involve creating several sets of pictures taken in different directions and also some 3-Dimensional (3D) pictures. With all of these different slices and 3D reconstructions, the radiologist will have a very detailed picture of the structures making up your body. This should help them to make a diagnosis (in other words, to understand the cause of your current problems) so that the right treatment can be planned as soon as possible.
You will receive instructions prior to your appointment. These instructions are very important as they may affect the accuracy of the test or require that the test be rebooked if you are not properly prepared for the CT scan. Depending on the type of scan that you are having, you may be asked to change into a gown to avoid parts of your clothing affecting the scan.
during your examination
The general process involves you lying on a bed attached to the scanner (this may be feet first or head first depending on the part of the body being looked at). The bed will then be raised up to a height level with the circular hole in the scanner and the bed slides in and out of the hole several times while pictures are being taken. It is important to try not to move during the scan as it will affect the quality of the pictures and make them harder for the radiologist to interpret. The radiographer performing the scan may ask you to hold your breath for some scans. The length of time for each breath hold is usually under 10 seconds. If your test requires an iodinated contrast injection, the radiographer will come into the room to administer it using either a hand held syringe or a mechanical pump. When the iodinated contrast is injected, most people will get a strange metallic taste in the mouth and feel a warm sensation through the body. This warm sensation may concentrate around the groin or buttock region and can feel like you may have wet yourself, even though you have not. Do not be concerned if this happens, it is a common sensation and usually goes away within a couple of minutes. Once out of the scanner room, it is likely that you will be shown to an area where someone will check with you to make sure that you are feeling OK after the scan. They will then remove the cannula so that you can go home.
ARE THERE ANY AFTER EFFECTS OF COMPUTED TOMOGRAPHY?
If you have an injection of iodinated contrast, the sensations of warmth and the strange taste usually experienced should go away within a few minutes. In very uncommon cases, some people may be allergic to the iodinated contrast. It is not possible to predict if a person will be allergic to the iodinated contrast, though the staff at the radiology practice are well trained to deal with allergic reactions should they arise. People who are allergic to the iodinated contrast used in CT may get some of the following symptoms:
- A skin rash or hives
- Sneezing and/or watering eyes
- Dizziness and/or headache
- Gagging or feeling of suffocation or swelling of the inside of the throat or mouth
- Change in blood pressure
If you do feel any of these symptoms after your scan, it is important to tell the radiographer or nurse immediately. If these feelings come on after leaving the radiology practice, you should return there immediately (if this is close by) or attend the nearest doctor or emergency department.
HOW LONG DOES COMPUTED TOMOGRAPHY TAKE?
CT scans that do not require an injection or much preparation are usually quite quick and may be completed within 5 minutes. Even when you are having a scan that requires an injection or other preparation, the length of the scan itself is usually under 10 minutes.
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