What is the role of added filtration placed outside the tube path?

• A. Inherent filtration reduces patient dose.
• B. Added filtration outside the tube path reduces patient dose by absorbing low-energy photons.
• C. Be window reduces dose.
• D. No filtration reduces dose.

Answer: (B)

Filtration helps shape the x‑ray beam by removing photons that don’t contribute meaningfully to an image but do increase patient dose. When filtration is added outside the tube path, it sits in the beam after the x‑rays leave the tube and collimator. It preferentially absorbs low‑energy photons, which are easily stopped by superficial tissues and add to dose without improving image quality. By removing those soft photons, the beam becomes “harder” (higher average energy), lowering skin and organ dose while preserving the photons that actually help form the image. The Be window is a form of inherent filtration inside the tube, so while it also reduces dose, the statement about added filtration outside the tube path specifically describes the external filtration’s role. Without any filtration, more low‑energy photons would reach the patient, increasing dose.