Kilovoltage (kVp) determines what aspect of X-rays?

• A. Penetration ability and the resulting image contrast
• B. Beam diameter
• C. Temperature of the tubehead
• D. Film processing time

Answer: (C)

Kilovoltage controls the energy of the X-ray photons produced. That energy determines how well the photons penetrate tissues and how differences in tissue absorption show up in the image. When you raise kVp, photons are more penetrating, so the image tends to have less contrast (more gray tones) because differences between tissues become less pronounced. When you lower kVp, photons are less penetrating, increasing subject contrast and making differences between tissues like enamel, dentin, and pulp more distinct.

Other factors in the choices aren’t set by kVp: beam diameter is controlled by collimation; the temperature of the tubehead is determined mainly by the tube current (mA) and exposure time; and film processing time relates to the developing process, not the exposure energy.