What is beam hardening and how filtration influences it?

• A. Filtration reduces overall beam intensity but does not affect energy spectrum.
• B. Beam hardening occurs when high-energy photons are absorbed by patient increasing contrast.
• C. Beam hardening refers to removing low-energy photons to create a more penetrating beam; filtration increases beam quality by hardening the spectrum and reducing patient dose.
• D. Beam hardening is the process of increasing beam energy by adding filtration, which raises patient dose.

Answer: (C)

Beam hardening is the process of removing the soft, low-energy photons from the X-ray beam so the remaining spectrum has a higher average energy. Filtration is the means to do this: by placing material in the path of the beam, those low-energy photons are absorbed before reaching the patient. The result is a harder, more penetrating beam with better beam quality, and it also reduces patient dose because the photons that would deposit most of their energy in superficial tissues (and contribute little to image formation) are removed. Of course, increasing filtration can also alter image contrast, since the higher-energy photons interact differently with tissues, so the amount of filtration is chosen to balance dose, penetration, and image quality.