Which set lists the three primary interaction mechanisms for diagnostic-energy photons in matter?

• A. Rayleigh scattering, Compton scattering, and Bremsstrahlung
• B. Photoelectric effect, Compton scattering, and pair production
• C. Photoelectric effect, Rayleigh scattering, and Compton scattering
• D. Photoelectric effect, Compton scattering, and Bremsstrahlung

Answer: (B)

At diagnostic-energy photon interactions with matter, the main processes are photoelectric absorption, Compton scattering, and coherent (Rayleigh) scattering. The photoelectric effect dominates at lower energies and higher atomic number materials, Compton scattering is the dominant inelastic process for many tissues at typical diagnostic energies, and Rayleigh scattering is elastic (coherent) scattering that can occur without energy loss. Pair production, while possible, has an energy threshold of about 1.02 MeV, so it isn’t a primary mechanism in diagnostic radiography. Bremsstrahlung describes photon production in the x-ray tube, not how photons interact with matter once they’re in the patient. Therefore, the best trio for diagnostic-energy photon interactions is photoelectric effect, Rayleigh (coherent) scattering, and Compton scattering.