What is backscatter and how does it affect image quality and patient dose?

• A. Photons scattered within tissue that travel back toward the receptor; can degrade image contrast and contribute to patient dose.
• B. Photons scattered away from the receptor, reducing image noise.
• C. Light emitted from the receptor after exposure.
• D. A form of interference that improves image sharpness.

Answer: (A)

Backscatter refers to photons that scatter inside the patient’s tissues and travel back toward the image receptor. These scattered photons add exposure to the image receptor from directions other than the primary beam, producing a background fog that reduces image contrast. At the same time, those photons deposit energy in the tissue, increasing the patient’s absorbed dose. In practice, higher kVp and larger field sizes increase backscatter because more photons undergo scattering (especially Compton scattering) and some of those scattered photons escape back toward the receptor. The main takeaway is that backscatter both degrades image quality by lowering contrast and raises patient dose by adding unintended exposure.