Computerised Tomography (CT Scan)

Post your experience
See others (3 there)

How is a CT scan done?

The CT scanner looks like a giant thick ring. Within the wall of the scanner there is an x-ray source. Opposite the x-ray source, on the other side of the 'ring', is an x-ray detector. You lie on a couch which slides into the centre of the 'ring' until the part of the body to be scanned is between the x-ray source and detector. The x-ray machine and x-ray detector both rotate around your body, always being opposite each other. As they rotate around, the x-ray machine emits thin beams of x-rays through your body which are detected by the x-ray detector.

The detectors detect the strength of the x-ray beam that has passed through the body. The more dense the tissue, the less x-rays pass through. The x-ray detectors feed this information into a computer. Different types of tissue with different densities show up as a picture on the computer monitor as different colours or shades of grey. So, in effect a picture is created by the computer of a 'slice' (cross section) of a thin section of your body.

The couch is then moved slightly further through the 'ring' to get a picture of the next section of your body. So, several cross sectional pictures or 'slices' of the part of your body being investigated are made by the computer. Newer scanners can even produce 3-dimentional pictures from the data received from the various 'slices' of body.

What is a CT scan used for?

A CT scan can be done on any section of the head or body. It can give clear pictures of bones. It also gives clear pictures of soft tissues which an ordinary x-ray test cannot show such as muscles, organs, large blood vessel, the brain and nerves. The most commonly performed CT scan is of the brain to determine the cause of a stroke. Other uses of a CT scan include:

• To detect abnormalities in the body such as tumours, abscesses, abnormal blood vessels, etc, when they are suspected by symptoms or other tests.
• To give a surgeon a clear picture of an area of your body before certain types of surgery.
• To pinpoint the exact site of tumours prior to radiotherapy.

What preparation do I need to do before a CT scan?

Usually very little. It depends on which part of your body is to be scanned. You will need to remove any metal objects from your body such as jewellery, hairclips, etc. It is best not to wear clothes with metal zips, studs etc. You may be asked to not to eat or drink for a few hours before your scan.

In some situations, depending on what part of the body is being scanned, one of the following may be needed. These aim to block a certain amount of x-ray going through various tissues. This helps to give better contrast between different organs and tissues on the scan pictures.

• For abdominal and pelvic scans you may be asked to have a special drink before the scan. This helps to show up the stomach and bowel more clearly.
• For pelvic scans, some fluid may be put into your rectum (back passage).
• For pelvic scans, women may be asked to insert a tampon into the vagina.
• Sometimes a dye (contrast medium) is injected into the bloodstream via a vein in your arm. The dye may give you a flushing feeling and an odd taste in your mouth which soon goes.

The CT scan itself is painless. You cannot see or feel x-rays. You will be asked to stay as still as possible as otherwise the scan pictures may be blurred. The scan can take about 20 - 60 minutes, depending on which part(s) of the body are scanned. It may be a little uncomfortable lying still on the couch for this time. Some scan operators play music to help you relax.

Can anybody be with me during the scan?

Because the scan uses x-rays, other people should not be in the same room. The operator controls the movement of the couch and scanner from behind a screen or in a separate control room. (This protects them from repeated exposure to x-rays.) However, you can talk to them, usually via an intercom, and you will be observed at all times on a monitor.

Some people feel a little anxious or claustrophobic in the scanner room when they are on their own. A mild sedative may be offered if you are particularly anxious. Small children may need a general anaesthetic to keep them still long enough for the pictures to be taken.

Are there any possible complications?

Complications are rare. The dose of x-ray radiation needed for a CT scan is generally quite low. So, the risk of harm is very small and it is considered a safe test.

Rarely, some people have an allergic reaction to the contrast dye which is sometimes used. This can be treated immediately. Very rarely the dye may cause some kidney damage in people who already have kidney problems.

Pregnant women, if possible, should not have a CT scan as there is a small risk that x-rays may cause an abnormality to the unborn child.

What can I expect after the scan?

There are no after-effects from the scan. So, you can return to your normal activities as soon as the scan is over. However, if you had a sedative for the scan you will need someone to accompany you home. You will not be able to drive until the effect of the sedative wears off.

The pictures from the scan are studied by an x-ray doctor (radiologist) who sends a report to the doctor who requested the scan.

© EMIS and PIP 2006   Updated: February 2006