How is the x-ray beam changed by the addition of one HVL of filtration?

• A. 50% decrease in quantity
• B. 25% decrease in quantity
• C. 50% increase in quantity
• D. 100% decrease in quantity

Answer: (A)

One HVL is defined as the thickness of filtration that reduces the X-ray beam’s intensity to 50% of its original value. So adding one HVL of filtration cuts the photon quantity in half—the beam is attenuated to half its prior intensity. Filtration also hardens the beam by removing more low-energy photons, raising the average energy, but the direct consequence of one HVL is a 50% reduction in quantity. If you added more HVLs, the remaining quantity would follow (1/2)^n.