How does increasing kVp affect the X-ray beam?

• A. Decreases the mean photon energy and penetrating power; increases image contrast.
• B. No change to beam quality or contrast.
• C. Increases the mean photon energy and penetrating power; reduces image contrast.
• D. Only increases the photon quantity without changing quality.

Answer: (C)

Raising kVp increases the energy of the X-ray spectrum, so the mean photon energy goes up and the beam becomes more penetrating. Higher-energy photons are less readily attenuated by tissue, which reduces the differences in attenuation between various tissues and thus lowers image contrast. So the effect is greater beam quality and penetrating power, with a decrease in contrast. The other statements don’t fit because kVp does change beam energy (not just quantity), and a lower energy would actually increase contrast, while saying there’s no change in quality is incorrect.