What happens when you increase kVp with fixed mA and time?

• A. Increases beam energy and often overall patient dose; typically lowers image contrast.
• B. Decreases beam energy and reduces patient dose.
• C. Has no effect on dose or image quality.
• D. Always increases image contrast without changing dose.

Answer: (A)

Raising kVp makes the x-ray beam more penetrating and shifts its energy spectrum to higher energies. With the tube current and exposure time fixed, more photons reach the image receptor and deposit energy in the patient, so the overall dose tends to increase. At the same time, the higher-energy photons are less differentially absorbed by various tissues, which reduces subject contrast on the image. So increasing kVp with fixed mA and time leads to higher beam energy and often higher patient dose, while image contrast typically decreases. The other statements conflict with how beam energy, dose, and contrast respond to a higher kVp.