Basics of X-ray and Mammographic Systems

Kilovoltage (kVp)

Stands for "kilovoltage peak"
Voltage applied between target (anode) and filament (cathode) during exposure
Controls speed (kinetic energy) of electrons produced by filament when they strike target
Affects range of energies of x-ray spectrum
- X-ray beam contains photon energies from 0 up to the peak kilovoltage (kVp) applied to tube

kVp affects subject contrast
- As kVp increases, subject contrast decreases
- Subject contrast also affected by absorber's
  - atomic #
  - thickness
  - density
kVp affects penetrability of x-ray beam
- Higher kilovoltage more penetrating
- Lower kilovoltage less penetrating
kVp affects patient dose
- Higher kVp beam is more penetrating
  - Larger fraction of x-ray photons penetrate patient and reach receptor
  - Fewer photons must enter body for same number to reach receptor