What type of x-ray photons are preferentially removed by filtration?

• A. High energy photons
• B. Low energy photons
• C. Medium energy photons
• D. All photons equally

Answer: (B)

Low-energy photons are preferentially removed by filtration. Filtration serves to harden the X-ray beam by absorbing the lower end of the energy spectrum, which contributes little to image formation but adds dose to the patient. The filtration material more readily attenuates these low-energy photons, often through absorption processes in the filter itself, so they are blocked while higher-energy photons—which penetrate tissues more effectively and carry meaningful image information—pass through. Inherent and added filtration together shape the beam to higher mean energy, reducing patient dose without sacrificing diagnostic quality.