Which major interaction between x-ray photons and tissue is most likely to occur with tissues having high atomic number?

Which major interaction between x-ray photons and tissue is most likely to occur with tissues having high atomic number?

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

Answer: (B)

The photoelectric effect is the primary interaction in high‑Z tissues. In this process, the incoming x-ray photon is completely absorbed and an inner-shell electron is ejected. The likelihood of photoelectric absorption rises dramatically with atomic number (roughly proportional to Z cubed) and decreases with higher photon energy (about E to the third power in the diagnostic range). So bones, which contain higher‑Z elements like calcium, absorb more photons than soft tissue, leading to greater attenuation and higher image contrast. Compton scattering, while important, depends mainly on electron density and is less sensitive to Z; Bremsstrahlung describes x-rays produced by deceleration outside the tissue, not the interaction inside it; coherent (Rayleigh) scattering occurs only at very low energies and is negligible in diagnostic imaging. Therefore, the dominant interaction in high‑Z tissue is the photoelectric effect.

The photoelectric effect is the primary interaction in high‑Z tissues. In this process, the incoming x-ray photon is completely absorbed and an inner-shell electron is ejected. The likelihood of photoelectric absorption rises dramatically with atomic number (roughly proportional to Z cubed) and decreases with higher photon energy (about E to the third power in the diagnostic range). So bones, which contain higher‑Z elements like calcium, absorb more photons than soft tissue, leading to greater attenuation and higher image contrast.

Compton scattering, while important, depends mainly on electron density and is less sensitive to Z; Bremsstrahlung describes x-rays produced by deceleration outside the tissue, not the interaction inside it; coherent (Rayleigh) scattering occurs only at very low energies and is negligible in diagnostic imaging. Therefore, the dominant interaction in high‑Z tissue is the photoelectric effect.