What is the effect of beam restriction on image quality?

• A. Beam restriction decreases contrast
• B. Beam restriction has no effect on image quality
• C. Beam restriction increases noise
• D. Beam restriction increases contrast by reducing scatter radiation

Answer: (D)

Restricting the X-ray beam improves image contrast by cutting down scatter radiation that reaches the detector. When the beam is focused to the area of interest, fewer photons interact with surrounding tissue to produce scattered photons. Scatter adds a gray, foggy veil over the image, reducing the difference between bright and dark structures. By reducing this scattered component, the image becomes clearer and the details of different tissues stand out more—this is especially true at higher kVp, where scatter is more prevalent. If exposure isn’t adjusted to compensate for the smaller beam, there can be more image noise due to fewer photons reaching the detector, but the dominant quality change from beam restriction is the enhancement of contrast from reduced scatter.