Why are grids used for x-rays?

• A. To increase beam energy
• B. To reduce film fogging
• C. To hold the film in place
• D. To change the focal spot distance

Answer: (B)

Grids are used to reduce scatter radiation that reaches the film. When X-rays pass through tissue, some photons scatter in many directions rather than traveling straight to the film. This scattered radiation adds a background exposure on the film, causing fog and lowering image contrast. A grid, with thin lead strips separated by gaps, sits between the patient and the film. The lead strips absorb much of the scattered photons, while the primary beam—traveling in a more direct path—still reaches the film. This reduces fog and enhances contrast, making details easier to see. Because the grid also absorbs some primary radiation, you often need a higher exposure to maintain image brightness. Grids don’t increase beam energy, don’t hold the film in place, and don’t change the focal spot distance.