Explain the three major interactions of X-rays with tissue during a diagnostic X-ray. For the two most common interactions, explain what factors affects the likelihood of the interactions occurring?
Photoelectric effect – incident x-ray photon interacts and removes an inner shell electron (most likely to occur when x-ray photon has an energy just above the binding energy of an inner shell electron). The x-ray photon is absorbed. The likelihood is higher with:
- higher electron density
- higher Z-numbers / larger nucleus
- lower x-ray photon energies (except at the K-edge) (PE ~ Z3/E3)
Compton scatter – incident x-ray photon hits an outer/loosely bound valence shell electron, where the x-ray photon transfers some energy to the electron (recoil electron) and the x-ray photon changes direction with a decreased energy (Compton shift = shift of wavelength/frequency. The wavelength change of the scattered photon = 0.024 (1-cos scattered photo angle) = thus the scattered photon energy decreased with increasing scattered photon energy. Likelihood is higher with:
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