The amazing technology of a CT scan

CT scans are well recognised now; most people will have heard the term and many will have had one.

CT stands for Computerised Tomography which means nothing to most of us but in fact describes a system that employs an X-ray machine in conjunction with a scanner to transfer information onto a computer.

A CT scan is different from a standard X-ray because it has the ability to take pictures of cross-sections. An X-ray sends a single ray through your body, a CT scanner will send several beams at different angles for a complete picture. The rays that hit dense tissue such as bone are met with resistance which weakens the rays; the rays that go through less dense areas such as lungs will appear stronger, and through this information the linked computer determines the density of the tissues examined and produces various sets of measurements. All this is put together with the end result that the computer can display a clear cross-sectional picture of parts of the body which can be enormously useful to medical staff.

Originally, CT scanners were designed to take pictures of the brain, but now the pictures are used for a myriad of medical purposes. A CT scan can pinpoint tumours and can allow doctors to inspect the inside of a body without an operation, so that internal damage and injuries such as a torn kidney or spine problems can be identified. A CT scan can be used to assess types of lung disease, and it can be very useful in the planning of specific medical procedures.

There are new CT scanners being developed, but generally a scanner is a large ring shaped machine, a bit like a large doughnut, with openings at both ends and a hole through the middle. The patient usually lies down on a flat bed adapted onto a moving system so that it can be gently slid in and out of the scanner. The area to be scanned has to be in the centre of the machine, so you may enter it head or feet first; and sometimes only the top or bottom section of your body needs to be inside the scanner. The patient needs to remove items such as glasses and metal jewellery and during the scan keep as still as possible. This can be difficult for some people - a scan can last up to 20 minutes so it is a long time to lie still. Some people also feel a little claustrophobic inside the “tunnel” in the scanner but this is not usually a major problem. While all medical staff have to leave the room during the procedure you will always have full contact with them, usually through some sort of intercom system, so you are never left entirely on your own.

During the procedure, the scanner will rotate in very small movements, taking a series of pictures of the designated area. It does not touch the patient in any way and the noise is minimal, just a small machine noise as the scanner works.

In certain instances the patient has to undertake some special preparation before a CT scan. For instance, if an examination is to be made of the intestines, then a patient will probably be asked not to eat for six hours before the test and may be given a drink containing gastrografin, a liquid containing a special x-ray dye for clear visibility on the computer. An x-ray dye can also be injected into veins to enable more clarity in diagnosis.

CT scans are today considered very safe and although they involve a higher level of radiation than normal x-rays, the levels are carefully monitored for every patient. They offer enormous benefit to medical professionals and patients as well, but of course like so much of the highly technical equipment now available in hospitals, they are very expensive.

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