What is the function of a grid?

• A. Absorb primary radiation
• B. Absorb scattered radiation
• C. Absorb low energy radiation before it reaches the image receptor
• D. Absorb remnant radiation

Answer: (B)

Grids reduce scatter to improve image contrast by absorbing photons that have been deflected as they pass through the patient. When X-rays interact with body tissues, some photons scatter in many directions; these scattered photons reach the image receptor and create a hazy, low-contrast image. The grid, with its lead strips, preferentially absorbs much of this scattered radiation while allowing most of the primary beam to pass through the spaces between strips. This selective absorption restores image contrast and makes details more visible. Because the grid also absorbs some primary radiation, you’ll typically need to increase exposure (more mAs, or adjust techniques) to maintain the same receptor exposure. Filtration and other options address different roles—filtration removes low-energy photons before they reach the receptor, and remnant radiation includes both primary and scattered photons after the patient—whereas the grid’s job is specifically to reduce scatter and boost contrast.