Which interaction contributes most to image scatter in a diagnostic radiography setting?

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

Answer: (C)

In diagnostic radiography, image scatter mainly comes from Compton scattering. When a high-energy photon enters body tissue, it often collides with outer-shell electrons and is deflected, losing some energy in the process. The scattered photon can travel in any direction and still reach the image receptor, creating gray fog and reducing image contrast. This type of scattering is likely at the energies used in diagnostic imaging (roughly tens to a few hundred keV) and in common tissues, which is why it dominates scatter production.

Photoelectric absorption, by contrast, removes photons from the beam entirely instead of producing scattered photons, so it doesn’t contribute to scatter reaching the detector. Coherent scatter does occur but has a much smaller probability at diagnostic energies, so its impact on image scatter is lesser. Pair production requires photon energies above 1.022 MeV and is negligible in typical diagnostic radiography.