(2) Kilovoltage peak (kVp). The kilovoltage peak or kVp determines the
strength of the X-ray produced. The "k" is Latin for one thousand. The "v" in kVp
stands for voltage. Thousands of volts of electricity (kilovolts) are needed to send the
electrons from the cathode to the anode of the X-ray tube to produce X-rays suitable for
penetrating human tissue. (The kVp is measured in kilovolts because regular voltage
would lack the force to penetrate human tissue.) The "p" or peak in kVp stands for the
maximum voltage in each burst of electron energy, produced in the pulsations of current
within the X-ray tube. If you set the X-ray machine at 90 kVp, it means that each burst
peaks at 90,000 volts. The voltage is less before and after the peak. Increasing the
kVp increases the speed with which electrons travel from the tube filament across the
penetrating power. See figures 2-4 and 2-5.
Figure 2-4. X-rays are produced when electrons from a cathode filament accelerate
toward an anode target, where the electrons are stopped.