What is the material placed in the useful beam to absorb preferentially the less penetrating radiation?

• A. Collimator
• B. Filter
• C. Lead Shield
• D. Grids

Answer: (B)

The effective way to make the useful beam more penetrating is filtration. By placing a suitable material (like aluminum) in the path of the primary beam, low-energy photons are absorbed more readily than higher-energy photons. This preferential absorption “hardens” the beam, increasing its average energy, which reduces patient dose from the soft, less penetrating photons and can improve image quality because the remaining photons contribute more effectively to imaging. This is different from shaping the beam with a collimator, shielding with lead placed off the beam path, or using grids to reduce scatter after the patient.