A Computerised Tomography (CT) scan is a detailed image constructed from within the body by a specialised type of X-ray machine called a CT scanner. The machine sends out several beams of X-rays through the body from different angles simultaneously.
The strengths of these X-rays are analysed by a computer, which uses these information to construct a detailed image of body structures on a monitor for the doctor to interpret.
There have been significant improvements in imaging technology since CT scanners were first deployed over four decades ago. For instance, high resolution CT scanners can now be used to guide a needle into the body with accurate precision during a procedure to obtain tissue biopsy.
Uses of CT scans
The procedure generates information so accurate that diseases that could only be found at surgery or at autopsy in the past can now be detected easily by doctors after a CT scan. The machine is excellent for the evaluation of soft tissues such as the brain, neck, liver and other abdominal organs.
Other uses include the diagnosis of various types of cancers, vascular diseases, aneurysms of large arteries, diseases of the spine, the sinuses, internal injuries and the investigation of unexplained symptoms such as persistent pain, headaches or dizziness. A CT scan is quick, safe and non-invasive.
Preparing for CT scans
The type of clothing to be worn for the procedure depends on the study being conducted. Metal objects such as jewellery, dentures, hairpins or hearing aids must be removed from the body to prevent them from interfering with the quality of images.
Patients expected to receive intravenous contrast injection during the procedure are advised to abstain from food or drink a few hours before the scan to avoid stomach upset. Investigations to detect abnormalities in the gut usually require contrast medium to highlight relevant organs. The patients receive an oral contrast agent to drink about one to two hours before the procedure to enable the doctors distinguish the structures to be examined from other abdominal organs.
What happens during the scan?
The CT scanner has a doughnut shape with a mobile table in the middle. This facilitates movement of the patient through the scanner head first, or feet first, depending on the part of the body to be scanned. In most cases, no sedation is administered on the patient prior to the scan.
The patient must be motionless while the actual scan occurs, but this is often for only a few minutes.
