Infographics / X-ray Physics

Beam quality vs quantity & X-ray output factors

Three x-ray spectra (photon number versus photon energy) comparing three changes. Higher kVp shifts the spectrum right and up, raising the maximum energy (Emax equals kVp) and the photon number, so both quality and quantity rise. Higher mAs scales the same-shaped curve up with the same maximum energy, raising quantity only. Added filtration removes low-energy photons, raising mean energy and half-value layer (quality) while lowering total photon number (quantity), with Emax unchanged.

Beam quality versus quantity shown with x-ray spectra Three x-ray spectra (photon number versus photon energy) comparing three changes. Higher kVp shifts the spectrum right and up, raising the maximum energy (Emax equals kVp) and the photon number, so both quality and quantity rise. Higher mAs scales the same-shaped curve up with the same maximum energy, raising quantity only. Added filtration removes low-energy photons, raising mean energy and half-value layer (quality) while lowering total photon number (quantity), with Emax unchanged. Beam quality vs quantity: reading the x-ray spectrum Dashed grey = reference spectrum; solid = after the change. Vertical axis = photon number, horizontal axis = photon energy. photon number Higher kVp Emax rises (= kVp) Higher mAs Emax fixed Added filtration Emax fixed peak near one third of Emax photon energy photon energy photon energy Shifts right and up: higher max energy and more photons. Quality and quantity both rise. Set by kVp. Scales up only: same shape and max energy. Quantity rises, quality unchanged. Set by mAs. Low-energy photons removed: mean energy and HVL rise (quality up), total photons fall (quantity down).
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