To achieve uniform film density within +/- 0.10 OD, how should the X-ray beam relate to the bucky grid and film?

• A. The beam is perpendicular to the bucky grid and centered on the film
• B. The beam is parallel to the bucky grid and offset on the film
• C. The beam is perpendicular to the bucky grid and off-center
• D. The beam is at a 45-degree angle to the bucky grid

Answer: (A)

Uniform density across the image with a bucky grid comes from aligning the beam so it hits the grid straight on and stays centered on the film. When the x-ray beam is perpendicular to the grid, the rays pass evenly through the interspace gaps and are absorbed by the grid strips in a uniform way, avoiding grid cutoff that would create density variations. Centering the beam on the film keeps the grid’s focal range properly aligned with the imaging field, so the exposure remains uniform from edge to edge.

If the beam is angled or offset, grid cutoff occurs, and the density becomes uneven across the image, moving outside the +/- 0.10 OD target. A 45-degree angle or running the beam parallel to the grid would introduce such cutoff and nonuniformity.