What is the effect of filtration on beam energy and patient dose?

• A. Filtration removes high-energy photons, lowering beam energy and increasing patient dose.
• B. Filtration removes low-energy photons, increasing beam energy and reducing patient dose.
• C. Filtration has no effect on beam energy or patient dose.
• D. Filtration removes mid-energy photons, with no dose change.

Answer: (B)

Filtration removes the low-energy portion of the x-ray spectrum. Taking out these photons hardens the beam, so the average energy of the beam increases. Low-energy photons tend to be absorbed in superficial tissues and contribute a lot to patient dose without improving image quality. By filtering them out, patient skin dose (and overall dose) decreases, while the beam becomes more penetrating.

That’s why the best choice states that filtration removes low-energy photons, raises beam energy, and reduces patient dose. The other options describe removing the wrong portion of the spectrum or claim no effect, which doesn’t match how filtration changes the beam.