Which factors affect the quantity of scattered radiation?

• A. kVp, Field size, Part thickness, Tissue density (Z number)
• B. kVp only
• C. Filtration and collimation
• D. mAs and exposure time

Answer: (A)

Scatter radiation quantity is driven by how much tissue is irradiated and how photons interact within that tissue. Higher beam energy (kVp) increases the likelihood of Compton interactions, so more scatter is produced as energy rises. A larger field size irradiates more tissue, providing more opportunities for scattering. Greater part thickness adds more path length and tissue for photons to interact with, boosting scatter. Denser tissue (higher Z) has more electrons to cause scattering, so scatter increases with density.

Filtration and collimation reduce the amount of scatter reaching the image receptor by removing low-energy photons and limiting irradiated tissue, but the primary factors that set how much scatter is generated inside the patient are kVp, field size, part thickness, and tissue density. mAs/exposure time mainly changes the number of primary photons produced, which can affect scatter indirectly, but the four factors above are the main determinants of scatter quantity.