Which interaction has negligible effect on the image at diagnostic energies below about 70 kVp?

Which interaction has negligible effect on the image at diagnostic energies below about 70 kVp?

• A. Photoelectric interaction
• B. Compton interaction
• C. Coherent scatter
• D. Pair production

Answer: (C)

Coherent scattering (Rayleigh scattering) is an elastic process in which the photon is deflected without losing energy. Because it doesn’t transfer energy to the atoms and its probability falls off with increasing photon energy, its contribution to image formation is minimal in the diagnostic energy range, especially below about 70 kVp. In this range, image characteristics are mainly shaped by photoelectric absorption (which drives contrast, particularly in high-Z tissues) and Compton scattering (which causes image fog). Pair production requires photon energies above about 1.02 MeV, well above diagnostic energies, so it isn’t relevant here.

Coherent scattering (Rayleigh scattering) is an elastic process in which the photon is deflected without losing energy. Because it doesn’t transfer energy to the atoms and its probability falls off with increasing photon energy, its contribution to image formation is minimal in the diagnostic energy range, especially below about 70 kVp. In this range, image characteristics are mainly shaped by photoelectric absorption (which drives contrast, particularly in high-Z tissues) and Compton scattering (which causes image fog). Pair production requires photon energies above about 1.02 MeV, well above diagnostic energies, so it isn’t relevant here.