The widespread use of the common imaging modalities of CT, nuclear medicine and fluororoscopy, together with the spectactularly informative images that can be generated by them, can tend to create a “take-it for granted” attitude that can obscure the fact that all these techniques involve potentially dangerous ionizing radiation. The taking of images of a patient is a medical decision, in which the clear advantages of the images for the determination of accurate diagnoses nearly always clearly outweigh the small (but, crucially, not zero) risk of radiation usually associated with the techniques. It is true that constant technological advances introduced by the manufacturers of modern imaging systems are inexorably lowering the dose of radiation to which the patient is exposed. (The latest dual source CT systems can offer cardiac imaging in less than one second — so no more problems of breath holding — at a radiation dose of less than one milli-Sievert!).
Nevertheless, at a population level, exposure to radiation is increasing and has been estimated to have nearly doubled over the last two decades. The total amount of radiation associated with CT, nuclear medicine studies and fluoroscopy is increasing — a recent study shows that while these modalities only account for approximately a quarter of all imaging procedures involving radiation, they actually contribute nearly 90% of the annual exposure that patients receive from medical imaging. Paradoxically, part of the reason for this increase is that the lower radiation doses of modern systems mean that radiologists are less inhibited to take additional, confirmatory images, so that although each individual image may be taken with a low radiation dose, there may be so many more images than would previously be the case that, overall, total exposure is increased. It has been suggested that a patient would have to get 400 standard chest X-rays to be exposed to the same level of radiation as just one CT abdomen scan.
In other cases, it is the inherent complexity of modern imaging modalities, which means that well-intentioned attempts by hospital technologists to customise their system in an attempt to increase the quality of the image, actually results in an accidental but significant overdose of radiation exposure.
It should not be thought that such incidents are restricted to small, perhaps under-staffed peripheral hospitals where radiographers may have limited experience. In fact the most recent unfortunate cause célèbre of accidental radiation overdose occurred with CT perfusion brain scans at the prestigious and supremely well-equipped Cedars-Sinai Medical Center in Los Angeles (the so-called hospital of the stars).
All this has prompted the redoubtable FDA to get involved with a proposed three-pronged approach to attack the problem of unnecessary radiation. This will involve the establishment of recognized diagnostic radiation levels, improvement of institutional QA procedures and the issuing of requirements to manufacturers of imaging equipment to incorporate additional safety devices in their systems.
Although the legal jurisdiction of the FDA is limited to the US, the international nature of the imaging equipment supply business means that the repercussions of the latest FDA recommendations will ultimately be felt by radiologists around the world.