Which of the following is primarily used to reduce patient exposure by filtering out low-energy photons?

• A. Collimation
• B. Filtration
• C. Receptor holders
• D. Protective eyewear

Answer: (B)

Filtration of the X-ray beam is what this item is testing. By filtering out the low-energy photons, we remove the part of the spectrum that would be readily absorbed by the patient’s tissues and would contribute little to image formation. These soft photons increase patient dose without improving the image, so filtering them out—usually with aluminum in the beam—“hardens” the beam and lowers the patient’s radiation exposure while maintaining diagnostic usefulness. Collimation reduces exposure by limiting the exposed area of tissue, not by filtering energy. Receptor holders mainly aid positioning and do not change the beam’s energy, and protective eyewear protects the eyes from scatter rather than filtering the primary beam.