Which interaction does not contribute to patient dose?

Coherent scatter, also known as Rayleigh scatter, is an interaction that occurs mainly at low energies and involves the alteration of the photon direction without a significant transfer of energy to the interacting matter. In this process, incoming photons are scattered coherently by the atoms in the tissue, typically resulting in no ionization of the atoms. Because coherent scatter does not lead to energy transfer that could cause biological damage or contribute to patient dose, it is considered not to contribute to patient dose in the context of diagnostic imaging and fluoroscopy.

In contrast, the other interactions—photoelectric absorption and Compton effect—result in the absorption or scattering of energy that can lead to ionization of atoms and potentially contribute to patient dose. Photoelectric absorption involves complete energy transfer from the photon to an inner-shell electron, resulting in the electron being ejected from the atom and leading to ionization. The Compton effect describes the interaction of photons with outer-shell electrons, leading to partial energy transfer and scattering, which also contributes to dose.

Thus, coherent scatter stands out as the interaction that does not significantly impact the dose received by the patient during fluoroscopic procedures.