The minimum filtration for x-ray machines operating above 70 kVp is expressed in aluminum equivalence. Which option correctly represents this requirement?

• A. Lead equivalence (Pb Eq.)
• B. Aluminum equivalence (Al Eq.)
• C. Lead and Aluminum equivalence combined
• D. No filtration required

Answer: (B)

Filtration in diagnostic X-ray equipment is specified as aluminum equivalence. This means the required filter is described by the thickness of aluminum that would produce the same reduction in low-energy photons and the same beam quality as the actual filter used. Aluminum is chosen as the standard reference because its attenuation behavior in the diagnostic energy range provides a consistent, practical way to express beam hardening across different settings and tube voltages. Lead would overattenuate and isn’t used as routine filtration in the tube (it’s mainly shielding). So the minimum filtration above 70 kVp is communicated as aluminum equivalence, with the actual value given in millimeters of aluminum equivalent according to the applicable standard.