Which statement about kVp and photoelectric absorption is true?

• A. Increasing kVp increases the proportion of photoelectric absorption
• B. Increasing kVp decreases the proportion of photoelectric absorption
• C. Increasing kVp has no effect on the proportion of photoelectric absorption
• D. Increasing kVp causes a higher image contrast

Answer: (B)

Higher photon energy reduces the probability of photoelectric absorption. The photoelectric effect is highly energy-dependent and drops off rapidly as energy increases, while other interactions like Compton scattering become more relatively likely at higher energies. As kVp goes up, photons are more energetic, so a smaller fraction are absorbed photoelectrically, even though more photons may still interact in the material overall. This is why the statement that increasing kVp decreases the proportion of photoelectric absorption is the best choice. The others don’t fit because increasing energy does not increase photoelectric absorption, there is a real energy dependence, and higher kVp generally lowers image contrast due to more penetration and scatter.