What is the primary purpose of filtration in the X-ray beam?

• A. Increase beam energy
• B. Absorb low-energy photons to reduce patient dose
• C. Decrease image contrast
• D. Hardening beam to reduce exposure time

Answer: (B)

Filtration removes the low-energy photons from the X-ray beam. These soft photons contribute to patient dose but don’t meaningfully help form the image because they’re readily absorbed in superficial tissues and don’t penetrate to reach the detector. By filtering them out, the beam becomes harder, meaning its average energy increases. This lowers the patient’s skin and internal exposure while leaving the photons that actually contribute to image formation, improving the overall radiographic quality. Inherent filtration from the tube and added filtration (like aluminum) achieve this, and while a harder beam can slightly affect contrast depending on settings, the primary purpose is to reduce dose by removing unhelpful low-energy photons.