CAT scan, computerised tomography, scan
What is a CT scan of the head?
CT scan of the head is a CT scan of the brain and the skull bones. A CT scan is an imaging modality which uses special X-ray equipment to produce multiple pictures of the inside of the body which are then joined together by a computer to produce cross-sectional views of the area being studied, in this instance, the brain. The images are then examined on a computer monitor, or printed.
The CT scanner is a large machine with a tunnel, in the centre. A moveable table slides into and out of this tunnel. In the centre of the machine, the X-ray tube and electronic X-ray detectors are located opposite each other on a ring which rotates around you, measuring the amount of radiation being absorbed throughout your body. A special computer programme processes this information to create two-dimensional cross-sectional slices of your body, which are then displayed on a monitor.
Any instance where injury to the brain is suspected by your doctor, especially after motor vehicle accidents, contact sport injuries or falls. A CT scan of the brain is also done for suspected bleeding, tumours, stroke and infections of the brain. It gives detailed pictures of the anatomy of the brain and skull.
How should I prepare?
You will be given a gown to wear during the examination, but wear comfortable, loose-fitting clothes just in case. Metal objects including jewellery, eyeglasses, dentures, hearing aids and hairpins may affect the CT images and should be left at home or removed prior to your exam. Women should always inform their doctor or the radiographer if there is any possibility that they may be pregnant. Your doctor will decide if you need contrast.Because of the potential damage that contrast can cause to diseased kidneys, you should inform your doctor if you are a diabetic, suffer from high blood pressure or have other kidney diseases. It is also essential to mention if you have suffered previous reactions to contrast.
How is the procedure performed?
You might have a needle inserted into your arm or hand for intravenous (vein) contrast.
The radiographer will position you on the CT examination table. You will usually lie flat on your back. Straps and pillows will be used to help you maintain the correct position and to hold still during the exam. Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scan is being performed. With modern scanners the examination time for the brain CT will be approximately a minute or less.
If you are claustrophobic or restless, you may find a CT exam to be stressful, and might be given a sedative. You will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.
You will be alone in the exam room during the CT scan, however, the technologist will be able to see, hear and speak with you at all times. With paediatric patients, a parent may be allowed in the room, but will be required to wear a lead apron to prevent radiation exposure.
Cancer due to radiation is always a risk, but the radiation from a CT is less than a normal person receives from background radiation (cosmic rays from atmosphere) The benefit far outweighs the risks.
Risk is increased for the babies of pregnant mothers, so please inform your doctor prior to the examination if you may be pregnant.
Repeated examinations on children should be avoided.
Modern contrast agents have minimal risk of allergic reactions, although diseased kidneys could be further damaged, especially if you are dehydrated. Make sure that you drink at least 2 litres of water on the day of and after the examination.
Obese people might not fit on the scanner.