Grids with a ratio above 8:1 are recommended for use above what kVp level?

• A. 50
• B. 120
• C. 90
• D. 150

Answer: (C)

As kVp rises, scatter radiation increases and image contrast drops. A high-ratio grid (greater than 8:1) helps by rejecting more scatter, preserving contrast, but it also absorbs more of the primary beam, so you need to increase technique to maintain receptor exposure. The practical guideline is that once technique exceeds about 90 kVp, using a grid with a ratio above 8:1 becomes desirable to control scatter and maintain image quality. At lower kVp, scatter is less, so a lower-ratio grid is usually sufficient; using a high-ratio grid would unnecessarily raise exposure. While you might still use high-ratio grids at very high kVp (like 120 or 150), the threshold at which they become beneficial starts at around 90 kVp.