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Computerised axial tomography is a very useful and accurate method of anatomical scanning. The machine directs x-rays from different angles onto the part scanned . The x-rays are then picked up from the other end and analysed by a computer. Based on the amount of x-ray absorbed in each plane, the computer calculates a three dimensional image of the part scanned. If a contrast is injected into the arteries at the time of scanning, the arteries will "light up" and become more visible to the computer. This technique is very useful when studying aneurysms or arterial or venous injuries.
Preparations for this procedure will include the insertion of a venous line to deliver the vascular contrast. In some instances, an oral contrast may also be required. This is usually given an hour or so prior to the investigation. The procedure itself is very quick and involves positioning the patient on a sliding bed that moves horizontally through the centre of the machine. After positioning, the scan begins and patients are asked to hold their breath for few seconds. It is important that patients are comfortable holding their breath and lying still during this phase. The contrast is injected via a special pump. The injection is synchronised with the scan. A rushing warm sensation in the arm may be felt as a result of injecting the contrast.
There are no specific precautions to take following this investigation. If a contrast related allergic reaction is to develop, this usually occurs very early on and is treated accordingly. All venous lines will be taken out as the patient is made ready for discharge. The disadvantage of this technique is that it involves exposing the patient to radiation and contrast. Repeated exposure to radiation can be hazardous and attempts are always made to minimise the dose of radiation during these investigations. The contrast material given can have a harmful effect on the kidneys particularly in the presence of kidney disease. Very occasionally, an allergic reaction develops in response to the contrast. This usually occurs shortly following administration and may require immediate treatment with anti-allergy medication.
Admission: Day of Procedure Anaesthetic: Not required Stay in hospital: One to two hours Time off work: Two to three hours First follow-up appointment: 2 weeks |
The CT control room. The CT operator maintains constant contact with the patient in the scanner via an intercom system.
The CT scanner room. Whilst most patients will be on their own during scanning, they are constantly monitored by the operator. |
