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Photon Interactions with Matter
Photoelectric absorption builds contrast and patient dose; Compton scatter fogs the image and exposes staff.
The rule
As the beam passes through the patient, each photon is absorbed, scattered, or transmitted to the receptor. The difference in absorption between tissues, called differential absorption, creates the image. In the diagnostic range three interactions matter: photoelectric absorption, Compton scattering, and coherent scattering. Pair production needs at least 1.02 MeV and photodisintegration needs even more, so neither occurs at diagnostic energies.