Question

Which of the following are true with regard to materials and attenuation?

a. Following the Compton effect, the wavelength change of the X-ray photon depends on the atomic number of the material

b. Photoelectric absorption is the predominating mode of interaction in modalities using high-energy photons

c. The Compton effect is the predominating mode of interaction in soft tissues

d. Photoelectric absorption is the predominating mode of interaction in air

e. The Compton effect is the predominating mode of interaction in contrast medium

Answer 1

a. False. The Compton effect is independent of the atomic number of the material as it only involves free electrons whose binding energy is negligible.

b. False. As photon energy increases, the rate of photoelectric absorption decreases more than the Compton effect. Hence, at high photon energies, the Compton effect still predominates.

c. True. The Compton effect predominates in low-atomic-number materials e.g. air, water and tissue.

d. False. Photoelectric absorption predominates in high-atomic-number materials, e.g. lead and contrast medium.

e. False.