What units are used to measure the total filtration of the x-ray beam?

• A. millimeter (mm) aluminum equivalence (Al eq.)
• B. millimeter (mm) lead equivalent (Pb eq.)
• C. millisievert centimeters squared (mSv-cm^2)
• D. milligray centimeter squared (mGy-cm^2)

Answer: (A)

Total filtration is described using how much aluminum would be needed to produce the same attenuation of the x-ray beam. This is expressed as millimeters of aluminum equivalent (mm Al eq.). The idea is to standardize filtration measurements because aluminum is a consistent reference material for diagnostic-energy photons, so stating the filtration as Al thickness allows comparison across beams and equipment. The inherent filtration in the tube plus any added filtration together determine this value, reflecting how the beam spectrum is hardened by removing low-energy photons. The other units listed don’t describe filtration: they relate to dose or dose-area products, and lead equivalence is used for shielding rather than beam filtration.