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The articles published in the February 2001 issue of the AJR [1,2,3] concerning the exposure doses used in pediatric CT created quite a ruckus in the radiology community and, fanned by the accompanying media publicity, even managed to arouse concern within the general public at large. This is certainly most unusual for news about radiology. It was short-lived, however, as most such brouhahas prove to be.
And life for radiologists has returned to normal. In the interim, if not as an immediate result of reading the articles, but at least after being alerted by all the hullabaloo, many radiology sites, if not all of them, have since appropriately adjusted the exposure factors for pediatric CT by increasing the pitch and reducing the mAs as recommended by Donnelly et al. [3].
Now in this issue of the Journal, we explore the larger issue of CT manufacturers' recommended exposure factors in general—that is to say, in all forms of CT for adults as well as children. Ravenel et al. [4] broach the subject by reporting on their study of radiation exposure and image quality in chest CT. In short, these researchers found that they could obtain satisfactory diagnostic images, images that in no way compromised the quality of the diagnostic information, using an exposure of 120 mAs instead of their previous standard of 280 mAs. The reduction in exposure of more than 55% was accompanied by a reduction in effective patient dose from 6.0 mSv (mrem) to 2.6 mSv (mrem). Ravenel et al. maintain that "...balancing of dose and image quality should be performed explicitly to ensure that patient doses are kept as low as reasonably achievable" [4]. These researchers espouse a most laudable goal, one with which the vast majority of radiologists can agree.
The three articles appearing in the February 2001 issue also generated two commentaries [5, 6] that appear in this issue. Both commentaries include recommendations that mirror those of Ravenel et al. [4]: exposure doses in CT should be lowered and can be lowered without compromising diagnostic quality.
In the first commentary, Nickoloff and Alderson [5] chronicle the increase in utilization of CT, describing the frequency of utilization as well as the contribution that CT makes to the collective radiation exposure from all radiologic examinations of patients. In the United States, according to Nickoloff and Alderson, despite the fact that CT currently accounts for only 13% of all radiologic examinations, CT results in 30% of the collective patient radiation exposure dose for all radiologic examinations.
In the second commentary in this issue, Haaga [6] chronicles the contributions of the many previous researchers who have described how to adjust radiation exposure on CT scanners without compromising image quality. Incidentally, the good Dr. Haaga is not a "Johnny-come-lately" when it comes to the subject of dose reduction in CT. He first published on this subject some 20 years ago, in 1981 [7]. According to Haaga, there appears to be no question that exposure can be lowered without compromising the diagnostic quality of CT examinations. In fact, he describes several methods by which this can be accomplished.
In view of the preceding, why were radiologists unaware of the high radiation exposure to patients undergoing CT? Well, maybe some of us were aware but didn't do anything about it. Maybe we assumed that such an exposure was necessary. Or we may have believed that radiation exposure in CT was somebody else's responsibility: the manufacturers of scanners, the nuclear regulatory commissioners, or whoever. We may have thought that because CT accounts for only a small percentage of all radiologic examinations, we need not be concerned about the dose given. We may have thought that those patients requiring CT were truly sick or desperately ill, and, therefore, the risk of high exposure was warranted under these circumstances. Or maybe we considered high exposure to be a transient matter, believing that ultimately MR imaging would replace CT.
But whatever our previous thinking, the fact remains that radiologists have now been made aware of the high exposure doses in CT. And the demand for the use of CT is increasing, not decreasing. Lately, CT appears to be ordered at the slightest provocation, maybe not quite willy-nilly but certainly at the drop of a hat. And just as certainly, not all the patients are desperately ill. So the time has come for radiologists to make the effort to lower radiation exposure doses in CT for our patients. But how can that be accomplished?
Engineers design the equipment, and manufacturers make the equipment. Radiologists are doctors and are directly responsible for the patients. We decide how the equipment is to be used. We should prescribe lower exposure doses. But how do we do that?
Not long after CT was introduced, radiologists saw the need for faster CT examinations. We asked for CT equipment that could perform faster examinations, and we got it. Engineers designed the equipment. Manufacturers built it, and radiologists bought it. Radiologists then asked for finer detail. The manufacturers responded. The equipment was made, and we bought it. Radiologists saw a need for better and faster image reconstruction. Again, they made it, and we bought it.
Now radiologists, in league with our physicist brethren, must insist on lower radiation exposure to patients undergoing CT. If and when the manufacturers build such equipment, I am certain that radiologists will buy it.
So why is radiation exposure in CT so high? Probably because we radiologists have not insisted that patient exposure doses be lowered. It is time for us to do so.
References
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