When calculating new milliampere-seconds after increasing SID, which relationship is used?

The correct relationship to use when calculating new milliampere-seconds (mAs) after increasing the Source-to-Image Distance (SID) is the Inverse Square Law. This law states that the intensity of radiation (or exposure) is inversely proportional to the square of the distance from the radiation source. As SID increases, the amount of radiation that reaches the image receptor decreases, which necessitates an adjustment in exposure settings to maintain image quality.

In practical terms, if you double the distance (SID), the amount of exposure (intensity) received at the image receptor is reduced to one-fourth of its original value, because intensity decreases with the square of the distance. This relationship is crucial in radiography, as it helps technicians calculate the required mAs to compensate for changes in SID, ensuring that the image remains properly exposed.

The other choices, while related to radiographic techniques, do not specifically relate to adjustments needed when changing the distance in terms of exposure calculations. The Direct Square Law is relevant for calculating changes in exposure when you change mAs in proportion to the square of the distance, but it is not what directly applies in this question concerning SID adjustments. The Maintenance formula and Exposure time equation also involve different aspects of radiographic technique