Is there less scatter in CT imaging, and what causes it?

• A. No, scatter is more in CT
• B. Yes, due to higher energy
• C. Yes, tight collimation
• D. Yes, due to longer exposure times

Answer: (C)

The main idea is that controlling the irradiated volume reduces scatter. Scatter happens when x-ray photons undergo interactions inside the patient and are deflected into the detectors. By tightening collimation, the beam is restricted to the slice being imaged, so fewer photons interact in surrounding tissue and fewer scattered photons reach the detectors. This reduces scattered fog and improves image contrast.

Higher beam energy isn’t the reliable way to reduce scatter in CT and isn’t the primary cause of better contrast here, as scatter behavior with energy is not straightforward in the diagnostic range. Longer exposure times increase dose and noise but don’t decrease scatter. So the best way to achieve less scatter is tight collimation.