Which statement about filtration is correct?

• A. Inherent filtration is placed outside the tube
• B. Inherent filtration is built into the tube housing
• C. Added filtration is built into the tube housing
• D. Filtration has no effect on beam quality

Answer: (B)

Filtration serves to remove low-energy photons from the x-ray beam, hardening the spectrum and reducing patient dose while also affecting image quality. There are two types: inherent filtration, which is part of the x-ray tube itself, and added filtration, which is placed in the beam path outside the tube. Inherent filtration is built into the tube housing, including the glass envelope, insulating oil, and port/window; these materials attenuate low-energy photons before the beam exits the tube. Added filtration is an external sheet or inserts (often aluminum) placed between the tube and the patient to further reduce low-energy photons. Filtration changes beam quality by increasing the average photon energy (raising HVL) and improving penetration, alongside reducing skin dose and potentially altering image contrast. Therefore, the statement that inherent filtration is built into the tube housing is correct; the others misstate where filtration lies, or claim it has no effect on beam quality.