The CT Scan

Frequently Asked Questions

What is a CT scan and how does it work?

A CT (computerised tomography) scanner is a special kind of x-ray machine. Instead of producing an image (radiograph) from a single direction, the x-ray source is rotated around the patient - acquiring a cross-sectional image (tomogram) from many angles.

The x-rays from the beams are detected after they've passed through the body and their strength is measured. Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have been absorbed by denser tissue such as bone will be weaker.

A computer can use this information to work out the relative density of the tissues examined. The computer processes the results, displaying them as a two-dimensional picture shown on a monitor.

Are there any risks?

You'll receive a dose of x-rays, however it's very unlikely to cause harmful effects. If you have an injection of contrast you may experience a sensation of warmth and a metallic taste in the mouth. And very occasionally, temporary side effects such as nausea or an itchy rash may occur, but other reactions are extremely rare. If there's any chance that you may be pregnant you should tell us before the examination.

What does it involve?

For an abdominal CT you may be asked to drink a liquid to outline the bowel before commencing the examination. Or, you may need a small injection of contrast medium to assist the examination.

The scanner itself looks like a large doughnut. During the scan you'll lie on a bed, with the body part under examination placed in the round tunnel or opening of the scanner.

The bed then moves slowly backwards and forwards to allow the scanner to take pictures of your body, although it won't actually touch you. The length of the test depends on the number of pictures and the different angles taken.