X-ray penetration (quality) is determined by which factor?

• A. mA
• B. kVp
• C. Exposure time
• D. Source to image distance

Answer: (B)

Beam quality, or the penetrating power of the X-ray beam, is controlled by the kilovoltage peak (kVp). Higher kVp raises the mean energy of the photons, making them more capable of penetrating through tissues and reaching the detector. This is why increasing kVp increases penetration. The amount of radiation produced, which affects image brightness, is governed by milliamperage (mA) and exposure time; they change how many photons are generated, not how energetic each photon is. Source-to-image distance mainly alters the beam’s intensity and magnification, not its energy. Filtration and other factors can modify the energy spectrum as well, but among the options, kVp is the factor that determines penetration. Note that increasing kVp can reduce image contrast, so the exposure is balanced to maintain adequate visualization of anatomy.