Which of the following is NOT a mechanism of x-ray attenuation in tissue?

• A. Bremsstrahlung
• B. Coherent scattering
• C. Photoelectric absorption
• D. Compton scattering

Answer: (A)

Attenuation in tissue happens when x-ray photons interact with atoms, either being removed from the beam or redirected. The main interactions in diagnostic energies are photoelectric absorption, which removes photons from the beam and transfers energy to the atom; Compton scattering, which deflects photons and reduces forward intensity while transferring energy to a recoil electron; and coherent (Rayleigh) scattering, which is elastic and can redirect photons with little energy loss, contributing to attenuation along the original path.

Bremsstrahlung is not a tissue-interaction that attenuates the beam. It’s the production mechanism of x-ray photons in the x-ray tube, created when high-speed electrons are decelerated in the anode’s electric field. That production process, not the interaction inside tissue, is what generates the beam.