Which two of the following are the most common grid ratios used in fluoroscopy?

• A. 4:1, 6:1
• B. 5:1, 8:1
• C. 6:1, 10:1
• D. 8:1, 12:1

Answer: (C)

Grid ratio describes how tall the lead strips are compared to the interspace material, and it directly affects how well scattered radiation is removed from the image. In fluoroscopy you’re dealing with large fields and motion, so you want enough scatter suppression to improve contrast without forcing the patient dose up to impractical levels. The two most commonly used grid ratios in fluoroscopy are 6:1 and 10:1 because they provide a practical balance: 6:1 gives good contrast with a moderate dose penalty, and 10:1 offers stronger scatter control for larger patients or more demanding imaging, albeit with a higher grid factor. Other ratios exist, but they’re less common because they either don’t suppress scatter sufficiently (lower ratios) or demand noticeably higher exposure and stricter alignment (higher ratios).