When calculating exposure with grid factors, which parameter is changed?

• A. kV
• B. mAs
• C. Distance
• D. Time

Answer: (B)

When a grid is used, it absorbs part of the X-ray beam, so fewer photons reach the image receptor. To keep the same receptor exposure, you compensate by increasing the exposure level by the grid factor. The way to implement this is by raising the mAs, since milliampere-seconds directly control the amount of X-ray photons produced. You can achieve this by increasing the tube current or the exposure time (or both), which increases the overall exposure.

The energy of the beam, set by kV, mainly affects image contrast and penetration, not grid compensation. Changing distance would alter exposure through the inverse-square law, but grid factors specifically require adjusting mAs to offset the grid’s attenuation. Time is part of mAs, so adjusting mAs is the practical change to account for the grid.