Which of the following is a form of added filtration commonly included in the x-ray tube assembly?

• A. Insulating oil
• B. Glass envelope
• C. Tube port
• D. Aluminum plates

Answer: (D)

Filtering the X-ray beam is about removing low-energy photons that contribute to patient dose without improving the image. There are two kinds: inherent filtration, which comes from components already in the tube such as the glass envelope and insulating oil, and added filtration, which is extra material placed in the beam path to further reduce those low-energy photons. Aluminum plates are the standard form of added filtration because aluminum is durable, easy to manufacture, and provides predictable attenuation of low-energy photons without drastically changing the beam quality. The insulating oil and the glass envelope are part of the inherent filtration inside the tube, not added filtration, while the tube port is simply the beam opening and does not act as a filter.