What is the most important factor in the production of scattered radiation?

• A. Kilovoltage
• B. Part thickness
• C. Field size
• D. Tissue density

Answer: (C)

Field size determines the amount of tissue that is irradiated. Scatter is produced by x-ray photons interacting with atoms in the patient, so irradiating more tissue creates more opportunities for scattering. Increasing the field size expands the volume of tissue exposed, which directly increases the total number of scatter events and the amount of scattered photons that reach the image receptor. While kilovoltage, tissue thickness, and density affect how likely scatter is and the energy of the scatter, the overall quantity of scatter produced is driven most by how much tissue is irradiated. In practice, limiting field size is a key way to reduce scatter and improve image quality.