Which beam filter combination will have the greatest effect on reducing skin and organ exposure?

Which beam filter combination will have the greatest effect on reducing skin and organ exposure?

• A. .1 mm Cu + .5 mm Al
• B. .5 mm Cu + .5 mm Al
• C. .20 mm Cu + 1 mm Al
• D. 0.0 mm Cu + 1.5 mm Al

Answer: (C)

Filtration reduces skin and organ dose by removing low-energy photons that contribute to dose but not to image formation. The more effective the filtration is at hardening the beam, the greater the dose reduction to superficial tissues. Copper filters absorb low-energy photons more efficiently than aluminum because of their higher atomic number and density, so adding even a small amount of copper can improve beam hardening beyond what aluminum alone would achieve. The combination with 0.2 mm copper and 1.0 mm aluminum provides the best balance: it yields stronger beam hardening than options with less copper or with aluminum alone, leading to the greatest reduction in skin and organ exposure. Even though another option uses more total aluminum filtration, aluminum is less efficient per millimeter at removing the low-energy photons that contribute most to skin dose, so it doesn’t reduce exposure as effectively as the copper-containing mix.

Filtration reduces skin and organ dose by removing low-energy photons that contribute to dose but not to image formation. The more effective the filtration is at hardening the beam, the greater the dose reduction to superficial tissues. Copper filters absorb low-energy photons more efficiently than aluminum because of their higher atomic number and density, so adding even a small amount of copper can improve beam hardening beyond what aluminum alone would achieve. The combination with 0.2 mm copper and 1.0 mm aluminum provides the best balance: it yields stronger beam hardening than options with less copper or with aluminum alone, leading to the greatest reduction in skin and organ exposure. Even though another option uses more total aluminum filtration, aluminum is less efficient per millimeter at removing the low-energy photons that contribute most to skin dose, so it doesn’t reduce exposure as effectively as the copper-containing mix.