Filtration in an x-ray system serves what purpose?

• A. Removes high energy photons
• B. Increases beam intensity
• C. Focuses beam
• D. Removes low energy photons

Answer: (D)

Filtration removes low-energy photons from the x-ray beam. By cutting out these soft photons, the beam becomes harder, meaning the average photon energy increases. Low-energy photons contribute to patient dose without improving image quality because they are readily absorbed by tissues and don’t help form a diagnostic image. Filtration (inherent plus added filters like aluminum) preferentially absorbs these photons, so the transmitted beam delivers the needed penetrating power with less unnecessary dose. The beam’s intensity drops slightly because some photons are absorbed, and beam focusing is accomplished by the collimation and tube design, not filtration. High-energy photons remain, so filtration does not remove them.