Helical CT

Check Out the Parameters Used for Helical CT

Lee F. Rogers, MD, Editor in Chief:

Sorry to say, but kids can get overlooked. In most cases, I am sure this is not intentional. Maybe it is more benign neglect, "out of sight, out of mind." Nevertheless, oversights do occur, some of which are unfortunate. I am writing in the midst of our presidential campaign; I am therefore compelled to quickly add that these oversights, in our case, are not of a political nature, promises not kept—or worse, promises made with no intention of keeping them.

During elections, kids are pawns in the game. When grubbing for votes, politicians promise children health care and education because it sounds good to their parents and other voters. But their promises are often hollow. Once the election is over, these same politicians, knowing they can get away with this charade (because children can't vote), find all manner of excuses for not delivering.

But, as it turns out, we as radiologists should watch what we say; those in glass houses should not throw stones. It has come to light that in one way, at least, we radiologists may be as guilty as others when it comes to not watching out for children.

In this issue Brenner et al. [1] report on their assessment of the potential risks of cancer arising as a result of the increased use of CT in the pediatric population. They point out that the use of CT has significantly increased in children (for good and clinically sound reasons). But they warn that this increased usage carries with it a potential for excessive exposure to radiation. And furthermore, the excess exposure and concomitant increase in radiation dose result in an increased risk of cancer in this population.

The reason for the excess radiation dose is the common practice of using the same X-ray exposure factors for CT examinations of children as those used for adults. A report by Paterson et al. [2], also in this issue, tends to support this contention. However, such exposure factors are greater than those necessary to perform a satisfactory CT examination in children.

In fact, a perfectly satisfactory examination in a child can be obtained with approximately half the exposure dose used for an adult. Wait a minute, you may be thinking. How could that be? Radiologists certainly don't want to increase the risk of cancer in the children we serve. Radiologists can't be doing this intentionally. What's the deal?

Well, it turns out that, unlike radiography, CT allows considerable latitude in the exposure required to obtain a visually acceptable diagnostic image. In film-screen radiography, with which we are all so familiar, if the exposure factors used were greater than those required, we can tell immediately—the film is dark, and we are immediately made aware that both the film, and thereby the patient, have been overexposed.

This is in sharp contrast to a CT examination wherein, once set, exposure factors are not much of a consideration. CT images tend to look the same from case to case, kids and adults alike, even when the same exposure factors are used for both. The computer in the CT equipment makes the necessary adjustments. So if a child has been overexposed when undergoing CT, it was most likely not done knowingly or intentionally; radiologists and radiologic technicians may simply be unaware of the potential for danger.

Fortunately, the situation is not difficult to correct. Simply put, the only action required is to adjust the CT exposure parameters for infants and children. OK, so how do we do that? Your AJR has the answer in this issue.

Turn to the article by Donnelly et al. [3] to learn how to minimize radiation dose for pediatric body CT. These researchers give the complete rundown on how to proceed. They tell us how and why. The basic requirements are to adjust the mAs downward and increase the pitch. That's all there is to it. Get with it! Equipment manufacturers should engage themselves in a campaign to see that CT in children is accomplished with the lowest possible radiation dose.

This does not likely require any significant changes in hardware, if indeed it should necessitate any hardware changes at all. And, for that matter, no change or addition to the software should be necessary either. No purchase of a "pediatric package" should be required. The technician or radiologist should be able to accomplish the desired reduction in radiation dose simply by selecting the correct exposure factors, less mAs and more pitch.

It would be helpful if these pediatric examination exposure parameters could be selected automatically on the control panel. Manufacturers should see that this is available if they have not already done so. But basically, what is needed at this time is the dissemination of information regarding the risk of the present common practice and an outline of the simple adjustments that must be made to address this issue.

The articles by Brenner et al. [1], Paterson et al. [2], and Donnelly et al. [3] in this issue of our Journal serve this purpose. Manufacturers should join in and mount a campaign to accomplish these ends as well. There should be little objection to either their campaign or our necessity of adjusting CT exposure parameters for children. This one is a "no-brainer."

Once informed, radiologists and technicians alike will make the necessary adjustments to do what is right for the children we serve.

References Brenner DJ, Elliston CD, Hall EJ, Berdon WE. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR 2001;176:289 -296

Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR 2001;176:297 -301

Donnelly LF, Emery KH, Brody AS, et al. Minimizing radiation dose for pediatric body applications of single-detector helical CT: strategies at a large children's hospital. AJR 2001;176:303 -306

Am J of Roentgenology, February 2001,

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