X-ray quantity and quality

Last revised by Dr Hamish Smith on 29 Apr 2019

X-ray photon quantity refers to the number of photons produced during an exposure.

Factors influencing x-ray quantity includes:

  • peak voltage (kVp): beam quantity is approximately proportional to the square of the tube potential
  • generator type/voltage waveform: reducing ripple increases beam quantity
  • beam filtration: increasing filtration reduces beam quantity
  • distance from the beam: inverse square law
  • current (mA): beam quantity is directly proportional to current
  • exposure time (seconds): beam quantity is directly proportional to exposure time
  • anode material: beam quantity is directly proportional to the atomic number (Z) of the anode material

X-ray photons quality relates to the x-ray spectrum changes and the effective photon energy. The effective photon energy is approximately equal to between one third to one half of the maximum photon energy.

Factors influencing x-ray quality include:

  • peak voltage (kVp)
  • voltage waveform: reducing ripple increases quality
  • beam filtration: increasing filtration increases quality through beam hardening
  • anode material: photon energy depends on the binding energies of shells in the anode material

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