What is the effect of increasing filtration on beam quality?

• A. Increasing filtration hardens the beam and raises the half-value layer.
• B. Increasing filtration softens the beam and lowers the HVL.
• C. Filtration has no effect on beam quality.
• D. Filtration only affects exposure time.

Answer: (A)

Filtration removes the lower-energy photons from the x-ray beam. Those low-energy photons don’t contribute effectively to imaging and are absorbed more readily by matter, so taking them out lets the remaining photons have higher average energy. That makes the beam more penetrating, a process known as hardening the beam. The half-value layer (HVL) is a measure of beam quality—the thicker the material needed to reduce the beam’s intensity by half, the higher the beam’s penetrating power. As filtration increases and the spectrum becomes more penetrating, more material is required to achieve a 50% reduction, so the HVL increases. That’s why increasing filtration both hardens the beam and raises the HVL.