Before having a CT (computerised tomography) scan, you will be asked about any existing health conditions that you have, any medication you are taking and whether you have any allergies.
This is to make sure that there is no risk of an adverse reaction during the scan.
Women of childbearing age will also be asked if they are pregnant. CT scans are not recommended for pregnant women (unless there is an urgent medical reason) because there is a small chance that the X-rays could harm the unborn child.
You should tell the radiographer if you feel anxious or claustrophobic about having a CT scan. A radiographer is a healthcare professional who is trained to carry out X-rays and other types of scans. They will be able to give you advice to help you to feel calm and, if necessary, arrange for you to have a sedative (medication to help you relax).
The scan
Before the scan, you may be asked to remove your clothing and to put on a gown. You will also be asked to remove items of jewellery because metal interferes with the scanning equipment. If you are having a head scan, you may also be asked to remove contact lenses, dentures, hair clips and hearing aids.
The CT scanner is a large, circular-shaped machine. You will be asked to lie on your back on a motorised bed that can be moved in and out of the CT scanner. The radiographer will position the bed so that the part of your body being investigated is lined up with the scanner.
The radiographer will operate the scanner from an adjoining room. While the scan is taking place, you will be able to hear and speak to them through an intercom.
While each scan is being taken, you will need to lie very still and breathe normally. This ensures that the scan images are not blurred. You may be asked to breathe in, breathe out, or to hold your breath at certain points.
The X-ray unit inside the ring will rotate around you. Each time it goes round it creates a new X-ray scan. After each scan is completed, the bed will move forward a small distance.
Depending on the area of your body being investigated, a CT scan may last up to 30 minutes. You should be able to go home soon after the scan has been completed.
Contrast medium
For some CT scans, such as those investigating your brain or abdomen, you may be given contrast medium beforehand. This is liquid that contains dye that shows up clearly on the images of certain tissues or blood vessels. Contrast medium helps distinguish blood vessels from other structures in your body.
There are a number of ways that contrast medium can be given, depending on the part of your body being scanned. It can be swallowed in the form of a drink, given as an enema in your back passage or it can be injected into your bloodstream (given intravenously).
If your kidney function is poor, contrast medium may not be given intravenously because it can depress kidney function further.
In rare cases, contrast medium can cause an allergic reaction. You should tell the radiologist if you have had an allergic reaction to iodine or contrast medium in the past or if you have any other allergies.
Contrast medium is harmless and it will pass out of your body in your urine.
Your results
The results of your CT scan will not be available immediately. A computer will be used to process all of the information, which will then be analysed by a radiologist (a specialist in interpreting images of the body).
The radiologist will write a report and send it to your specialist or GP. Before leaving hospital you should ask when to expect your results. It will usually take a couple of weeks.
