'Full-body' CT scans: Are they worth the cost in money and radiation exposure? (page 2 of 2)
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In the last ten to 15 years, developments in general X-ray technology have driven examination doses down by as much as 50% for some procedures. Paradoxically developments in CT technology have pushed doses up. Improvements in scanning speed and the ability to perform extensive scan sequences (up to 1,200 slices for a single examination, compared with 40-50 on older scanners) increases the diagnostic potential but also increases the dose. Even if like-for-like scan sequences are performed on a modern multi-slice scanner the dose may increase by 20-40% compared to a conventional single slice machine.2 In 1989 CT scans accounted for 2% of all X-ray examinations but contributed 20% of the collective dose to the general population from diagnostic imaging.3 By 1998 these figures had risen to 4% of examinations and 40% of the collective dose.4 It is likely that the contribution from CT will continue to rise for a variety of reasons:
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Increased numbers of scans are being requested as more scanners are now available, the applications of CT scanning increase and because scans are used as a substitute for careful history taking, clinical examination and the application of clinical acumen and experience.
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New scanners can perform various reconstructions from the data introducing new, exciting examination techniques such as virtual colonoscopy or bronchoscopy and CT angiography. But these require large numbers of thin section slices for the reconstructions.
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In addition the ability to make multiple short scans through particular areas allows multiple vascular phase examinations (arterial, capillary, venous, parenchymal, etc.), or ‘real time’ CT fluoroscopy for interventional procedures.
Coming back to ‘full body’ CT scans for asymptomatic people, the Food and Drug Administration (FDA) in the US is of the view that ‘the harms [arising from these scans] currently appear to be far more likely and in some cases may not be insignificant’.5 So their advice would seem to be to keep your money in your pocket if you are in general good health.
Walk-in CT screening units will not be introduced in the UK (or elsewhere in Europe) since our legislation requires individual medical exposures to be justified in terms of potential benefit against radiation risk.6 However, it is important that all of us in the clinical community, both clinicians and radiologists, are aware of the doses involved in these ‘exciting’ new techniques. We should consider alternative imaging techniques such as ultrasound and magnetic resonance imaging (MRI) which, while not providing colour-coded 3D constructions of the mediastinum or abdominal structures, can still provide the diagnostic information necessary for patient management, without the significant exposure to ionising radiation. If a CT scan is required then every care should be taken to minimise the dose, particularly in paediatric cases, so that the necessary diagnostic information is obtained with the minimum patient exposure. Anyone requiring further information on this subject should read a recent review by Golding and Shrimpton, this provides an excellent summary of the issues involved.7
