What is the name of the unit for the maximum crest voltage between the anode and cathode of an X-ray tube, which determines the beam's penetrating ability?

• A. Kilovolt Peak (kVp)
• B. Milliamperage (mA)
• C. Watt
• D. Hertz

Answer: (A)

The energy with which X-ray photons are produced—and thus how deeply they penetrate tissues—is determined by the peak voltage across the tube. This peak voltage is measured in kilovolts and is called Kilovolt Peak (kVp). Increasing kVp raises the maximum photon energy, making the beam more penetrating and altering image contrast and dose. In contrast, milliamperage (mA) changes the number of photons (beam quantity) but not their energy; watt is the product of kVp and mA (tube power/heat), not the energy per photon; and hertz is a frequency unit unrelated to X-ray beam penetration.