What physical characteristic chiefly determines the amount of scatter reaching the image receptor in radiography?

• A. Subject age
• B. Ambient room temperature
• C. Image receptor speed class
• D. Tissue thickness

Answer: (D)

The amount of scatter reaching the image receptor is governed mainly by how much tissue the X-ray beam passes through. Greater tissue thickness means more material for photons to interact with, and the dominant interaction at typical radiography energies is Compton scattering. As thickness increases, more photons scatter in various directions, and a larger portion of those scattered photons reach the receptor, reducing image contrast. The other factors don’t determine scatter production: subject age doesn’t change the amount of tissue in a given exam, ambient room temperature has no effect on photon interactions, and image receptor speed class affects image detection and noise rather than how much scatter is produced.