Improper use of grids may result in an image artifact known as:

• A. SNR
• B. Moiré pattern
• C. Elongation
• D. Foreshortening

Answer: (B)

Grids improve image contrast by absorbing scattered radiation, but improper use can create a moiré pattern. A moiré pattern is an interference effect that happens when the grid’s regular lead-strip pattern interacts with the digital detector’s sampling pattern, producing visible, repetitive dark and light bands across the image. This aliasing occurs when a stationary grid is used with digital acquisition or when the grid frequency is too close to the detector’s sampling frequency, causing the grid lines to appear as a secondary pattern.

To prevent it, ensure the grid is properly aligned and moved (bucky) during exposure, or choose a grid frequency that won’t alias with the detector’s sampling. In digital systems, using a higher-frequency grid or introducing motion/rotation of the grid helps eliminate the artifact.

SNR is a measure of signal versus noise, not a pattern caused by grid interaction. Elongation and foreshortening are due to projection geometry and patient or beam positioning, not grid-related artifacts.