What is the primary purpose of proper alignment and centering when using a grid?

• A. To maximize scatter absorption
• B. To minimize exposure time
• C. To avoid grid cut-off and ensure uniform exposure across the image
• D. To improve patient comfort

Answer: (C)

Aligning and centering the grid is essential because the grid’s job is to reduce scattered radiation without compromising the primary beam. When the grid is properly aligned with the central ray and centered over the x‑ray field, the beams pass through the grid evenly and the lead strips absorb scatter uniformly. This prevents grid cutoff, where the primary photons are absorbed more in some parts of the image, causing uneven exposure and density across the image. Misalignment or off‑centering tilts the beam relative to the grid, leading to edge darkening or light bands and overall nonuniform image quality. Keeping the grid centered and properly aligned ensures a uniform exposure across the entire image and preserves image contrast, which is why this is the primary purpose.