The photoelectric effect is more likely to occur in tissue with which property?

The photoelectric effect is more likely to occur in tissue with which property?

• A. High atomic number tissue
• B. Low atomic number tissue
• C. High density tissue
• D. Low density tissue

Answer: (A)

Higher atomic number increases the likelihood of the photoelectric effect. In this process, a photon ejects an inner-shell electron, and atoms with larger atomic numbers have electrons that are more tightly bound, which raises the cross-section for this interaction—especially at the lower photon energies used in diagnostic imaging. As a result, high‑Z tissues (like bone, which has a higher effective Z than soft tissue) absorb more photons via the photoelectric effect than low‑Z tissues. Density affects overall attenuation but doesn’t determine the propensity for this interaction as strongly as atomic number does.

Higher atomic number increases the likelihood of the photoelectric effect. In this process, a photon ejects an inner-shell electron, and atoms with larger atomic numbers have electrons that are more tightly bound, which raises the cross-section for this interaction—especially at the lower photon energies used in diagnostic imaging. As a result, high‑Z tissues (like bone, which has a higher effective Z than soft tissue) absorb more photons via the photoelectric effect than low‑Z tissues. Density affects overall attenuation but doesn’t determine the propensity for this interaction as strongly as atomic number does.