Which interaction between x-ray photons and matter involves the greatest dose to the patient in diagnostic imaging?

Which interaction between x-ray photons and matter involves the greatest dose to the patient in diagnostic imaging?

• A. Bremsstrahlung
• B. Photoelectric effect
• C. Compton scatter
• D. Coherent/Classical

Answer: (B)

The key idea is how energy from x-ray photons is deposited in tissue. In the photoelectric effect, the photon is completely absorbed by an atom, and all of its energy goes into ionizing the atom and producing a photoelectron right there in the tissue. This means the energy deposited—and thus the absorbed dose—is concentrated at the interaction site and is essentially the full photon energy minus a small binding-energy amount. Because diagnostic energies are chosen where photoelectric absorption is relatively likely, this process delivers the most dose per interaction. Bremsstrahlung involves deceleration of the incident electron, producing a secondary photon, which may escape or be absorbed later, so the energy deposited per initial interaction isn’t as localized or as large. Compton scatter transfers only part of the photon's energy to a recoil electron, with the remaining energy often carried away by a scattered photon, reducing the dose deposited at the original site. Coherent (classical) scattering transfers very little energy and contributes negligibly to dose. So, among these interactions, photoelectric absorption deposits the greatest dose to the patient in diagnostic imaging.

The key idea is how energy from x-ray photons is deposited in tissue. In the photoelectric effect, the photon is completely absorbed by an atom, and all of its energy goes into ionizing the atom and producing a photoelectron right there in the tissue. This means the energy deposited—and thus the absorbed dose—is concentrated at the interaction site and is essentially the full photon energy minus a small binding-energy amount. Because diagnostic energies are chosen where photoelectric absorption is relatively likely, this process delivers the most dose per interaction.

Bremsstrahlung involves deceleration of the incident electron, producing a secondary photon, which may escape or be absorbed later, so the energy deposited per initial interaction isn’t as localized or as large. Compton scatter transfers only part of the photon's energy to a recoil electron, with the remaining energy often carried away by a scattered photon, reducing the dose deposited at the original site. Coherent (classical) scattering transfers very little energy and contributes negligibly to dose.

So, among these interactions, photoelectric absorption deposits the greatest dose to the patient in diagnostic imaging.