American Registry of Radiologic Technologists (ARRT) Practice Exam

The formula used to maintain image density when changing the distance in radiographic imaging involves the relationship between the initial and final milliamperage-seconds (mAs) and the distances at which those settings are applied. The correct calculation shows that the mAs must be adjusted based on the square of the ratio of distances to ensure consistent radiographic density.

Specifically, when distance changes and you want to maintain the same density on the radiograph, you take the initial mAs and multiply it by the square of the ratio of the initial distance to the new distance. This reflects the inverse square law, which states that as the distance from the radiation source increases, the intensity of radiation decreases with the square of the distance. Therefore, to keep density constant despite the change in distance, the mAs must be increased or decreased accordingly using the squares of the distances involved.

This understanding is crucial in radiologic technology as it ensures that images are neither too dark nor too light, which can affect diagnostic quality. The other formulas do not accurately express this relationship, making the first option the correct one for this particular situation.