Lab Tests Online - Explaining Pathology

Glossary

CT scan


Also known as: Computed tomography, CAT scan

What is it?
The scanner is a doughnut shaped machine that takes x-rays of your body. This test is not performed in a Pathology laboratory but may well be requested at the same time as laboratory tests.
How does it work?

The machine produces a series of narrow beams as it moves through an arc around the body. The beams are detected after passing through the body. Beams that pass through dense tissue will be weaker and those that pass through less dense tissue will be stronger. A detailed two dimensional picture can then be produced from these x-rays which is not possible from a simple x-ray.

There is now a relatively new scanner called spiral CT that is quicker and more accurate for many diseases. The x-ray beam makes a continuous spiral path with no gaps between images.

What is it used for?

Scans can give detailed views of bone, lungs, soft tissue and blood vessels and are commonly used to investigate the head and abdomen. The brain may be investigated for tumours or bleeding while scans of the abdomen can give information about tumours, tears of organs (following a road accident), or enlarged or inflamed organs. It is also useful for guiding needles when taking tissue biopsies.

How is it carried out?

The patient must remove all metal objects before lying on a motorised couch that passes through the hole of the machine. A contrast medium may be given, by mouth, injection or enema, to improve the sharpness of the images. The patient usually lies on their back but may be asked to lie on their side or front. You will be asked to lie very still but breathe normally. After each x-ray the couch will be moved forward a small amount. The scan lasts from a few minutes to about thirty minutes.

What are the risks?

CT scans are considered very safe and use low amounts of radiation. They are quick and accurate and eliminate the need for invasive surgery.

Pregnant women should not have a CT scan. Nursing mothers should wait 24 hours after a scan before resuming breast-feeding.

The contrast media often contain iodine. Some people are sensitive to iodine and have an allergic reaction. If you know that you are allergic to iodine or have other allergies you should tell the doctor. Very rarely the contrast medium can cause kidney damage in patients who already have kidney problems.