Question

Concerning the interaction of X-ray photons with matter: 

a. It is possible to predict the fraction of photons that will be absorbed or scattered, when passing through a given material 

b. Attenuation is represented by the number of photons absorbed or scattered by matter 

c. Scattered photons help form the primary image on the film 

d. The half-value layer (HVL) of a material is the thickness needed to reduce the number of photons in a beam by half 

e. The HVL is inversely proportional to the linear attenuation coefficient (LAC) of a material

Answer 1

a. False. X-ray absorption and scatter are stochastic processes. 

b. True. Attenuation is the total number of photons that have been removed, as a result of scatter or absorption, from the primary beam after passing through the attenuated material. 

c. False. The X-rays transmitted through the patient form the primary image, while the scattered X-rays obscure it. 

d. False. The HVL is the thickness of a material that will reduce the intensity of a mono-energetic beam to half its value, not the number of photons. 

e. True. The LAC is the probability that a photon interacts (absorbed or scattered) per unit length it travels in a specific material. Hence, the greater the LAC, the lower the HVL of the material.