Which operator console knob controls x-ray beam quality?

• A. Milliampere (mA)
• B. Exposure time
• C. Source-to-image distance
• D. kVp

Answer: (D)

Beam quality means how penetrating the X-ray beam is, which depends on the energy of the photons. The kilovoltage peak (kVp) knob on the operator console sets that energy. Higher kVp increases photon energy, producing a more penetrating beam and altering image contrast. The other controls affect how many photons are produced or how the beam interacts with the geometry, not the energy: milliampere (mA) changes the tube current and thus the number of photons (beam quantity); exposure time changes how long the tube is on (also a quantity factor); and the source-to-image distance affects magnification andIntensity rather than photon energy. So the knob that controls beam quality is the kilovoltage peak setting.