What is the role of filtration in x-ray beams?

• A. Filtration removes low-energy photons to harden the beam, reducing patient skin dose and improving image contrast; it also helps meet standards for beam quality.
• B. Filtration increases the number of photons for better receptor exposure.
• C. Filtration reduces scatter after exposure.
• D. Filtration converts x-rays to visible light for alignment.

Answer: (B)

Filtration serves to remove the lowest-energy photons from the beam. Those soft photons would be absorbed in superficial tissues, contributing to patient skin dose without providing useful information. By filtering them out, the beam becomes harder — the average photon energy increases — which reduces patient dose and improves image contrast because the remaining photons penetrate more consistently and produce a clearer signal. Filtration also helps meet beam-quality standards by increasing the HVL (half-value layer), a measure of beam hardening.

Filtration does not increase the number of photons reaching the receptor; in fact, it lowers the overall photon fluence while improving dose efficiency. It does not specifically reduce scatter after exposure (that’s the job of grids and geometry). It also does not convert x-rays to visible light—that function belongs to the phosphor in imaging screens or detectors.