What is the unit for the maximum or crest value of the electrical potential difference between the anode and cathode of an X-ray tube, which determines the maximum penetrating ability of the X-ray beam?

• A. Milliampere
• B. KILOVOLT PEAK (kVp)
• C. Exposure time
• D. Filtration

Answer: (B)

The maximum penetrating ability of the X-ray beam is determined by the energy of the photons, which comes from the peak voltage applied across the tube. The crest value of this voltage sets the maximum energy that electrons gain before they hit the anode, and thus the maximum energy of the produced photons. The unit describing this crest value is kilovolts peak (kVp). Increasing kVp raises the maximum photon energy and makes the beam more penetrating. In comparison, milliampere affects how many photons are produced (the beam’s quantity), exposure time changes how long the beam is on, and filtration alters the beam spectrum but not the maximum energy.