What is the role of collimation in dose management and image quality?

• A. Collimation enlarges the field of view to include surrounding anatomy.
• B. Collimation narrows the beam to the region of interest, reducing patient dose and scatter, and improving image quality by reducing off-field exposure.
• C. Collimation has no effect on dose.
• D. Collimation only affects processing time.

Answer: (B)

Collimation narrows the x-ray beam to the region of interest, which directly reduces the volume of tissue exposed. With less tissue irradiated, fewer photons are scattered, so there is less fog on the image and better contrast. Fewer photons from outside the area of interest reach the detector, which also helps prevent off-field exposure from degrading diagnostic quality. In short, tighter collimation lowers patient dose and improves image quality by reducing scatter and off-field exposure. The other ideas—expanding the field, having no dose effect, or affecting processing time—do not apply.