Energy of the x-ray photons produced is primarily determined by:

• A. mAs
• B. kVp
• C. mA
• D. SID

Answer: (B)

The energy of x-ray photons is determined primarily by the kilovoltage across the x-ray tube. This tube potential accelerates electrons to higher kinetic energy, and when these electrons interact with the target, the photons produced (especially in bremsstrahlung) can have higher energies as the electron energy increases. Higher kVp raises the maximum photon energy and shifts the spectrum toward higher energies.

In contrast, mAs controls how many photons are produced (the beam’s quantity) by affecting the current and exposure time, not their energy. SID affects beam intensity at the image receptor through inverse square law and beam geometry, not the energy of the photons.