The thickness of added filtration within general-use x-ray tube assemblies is approximately:

• A. 4 mm
• B. 2 mm
• C. 1 mm
• D. 3 mm

Answer: (B)

Added filtration is a modest amount placed in the beam path to remove the low-energy photons that contribute to patient dose but don’t improve image quality. In general-use x-ray tube assemblies, this filtration is chosen to reduce skin radiation without making the beam too weak for typical imaging tasks. By filtering out the lower-energy portion of the spectrum, the beam becomes harder (higher average energy), which increases the beam’s half-value layer. That means, to maintain the same image receptor exposure, you may need to raise exposure factors. Too little filtration would leave excess low-energy photons and higher patient dose; too much filtration would degrade image brightness and could require compensating changes that defeat the dose savings.