If you change from a nongrid technique with 10 mAs at 75 kVp to using a 12:1 grid at 75 kVp, what mAs is needed to produce the same image?

If you change from a nongrid technique with 10 mAs at 75 kVp to using a 12:1 grid at 75 kVp, what mAs is needed to produce the same image?

• A. 50 mAs
• B. 2 mAs
• C. 40 mAs
• D. 120 mAs

Answer: (A)

When a grid is added, the grid absorbs part of the primary beam, so fewer X-ray photons reach the image receptor. To maintain the same image density, you must increase the exposure by the grid factor (also called the bucky factor). For a 12:1 grid at 75 kVp, the grid factor is about 5. Multiply the nongrid mAs by this factor: 10 mAs × 5 ≈ 50 mAs. Keeping the kVp the same preserves contrast, while the higher mAs compensates for the grid’s attenuation. Other mAs values would either underexpose or overexpose the image and thus not yield the same receptor exposure.

When a grid is added, the grid absorbs part of the primary beam, so fewer X-ray photons reach the image receptor. To maintain the same image density, you must increase the exposure by the grid factor (also called the bucky factor). For a 12:1 grid at 75 kVp, the grid factor is about 5. Multiply the nongrid mAs by this factor: 10 mAs × 5 ≈ 50 mAs. Keeping the kVp the same preserves contrast, while the higher mAs compensates for the grid’s attenuation. Other mAs values would either underexpose or overexpose the image and thus not yield the same receptor exposure.