CT Scanning

WHAT IS A COMPUTED TOMOGRAPHY OR COMPUTERISED AXIAL TOMOGRAPHY (CT)?   A CT scan, sometimes also called a CAT scan, takes pictures of the body and uses a computer to put them together. CT stands for computerised tomography and is a painless procedure. As series of X-rays are taken of the body at slightly different angles, to produce very detailed images of the inside of the body. The images produced by CT scans are called tomograms and they provide doctors with information to help them reach a diagnosis about a variety of conditions.

WHY IS IT NECESSARY?

Because of the way CT images are produced, they have advantages over normal X-ray images in distinguishing between different types of soft tissue. CT scans can be performed on any part of the head or body and are particularly good for:

internal organs within the abdomen and chest – e.g. liver, kidneys, pancreas, intestines, lungs, bone imaging for orthopaedic examinations, brain imaging – e.g. to determine the cause of a stroke, and vascular imaging – examining blood flow to different parts of the body.

HOW IS IT PERFORMED?

When you have a CT scan, you will be required to lie ona motorised bed inside the scanning machine which looks like a giant doughnut.

After each X-ray is completed, the bed on which you are lying is moved forward a small distance. You will be asked to lie very still while each scan is taken to avoid blurring the images. Several scans will be carried out and the whole procedure may last up to 30 minutes depending on the type of scan.

HOW DOES IT WORK?

A CT scanner uses a series of X-ray beams to build up images of the body in slices. Unlike an X-ray, which sends one beam of radiation through the body, a CT scanner emits a succession of narrow beams as it moves through an arc. This produces a very detailed image.

The detector within a CT scanner can see hundreds of different levels of density, including tissues within solid organs such as the liver. This information can then be sent to a computer, which builds up a cross-sectional image of the body and displays it on the screen. Depending on the part of the body being examined, a dye may be given by injection and used to make some tissues show up more clearly. For scans of the abdomen, you might be given a drink containing barium. This is known as a “barium meal” and shows up white on the scans as it moves through the digestive tract.