What is the role of a collimator in beam geometry and patient dose management?

• A. Defines field size, reduces exposure to surrounding tissue, minimizes scatter, and improves image quality by restricting the beam.
• B. Increases field size.
• C. Does not influence scatter.
• D. Only affects beam energy.

Answer: (A)

The main idea tested is how a collimator shapes and confines the X-ray beam to the area of interest, which directly affects patient dose and image quality. By defining the field size, the collimator ensures only the intended tissues are irradiated, reducing exposure to surrounding tissues. Limiting the beam also lowers the amount of scatter produced and that reaches the image receptor, which improves image contrast and sharpness. The collimator does not change the photon energy—the energy is set by kilovolt peak and filtration—nor does it increase the field size; its job is to constrain it. So this option captures that the collimator defines field size, reduces exposure to surrounding tissue, minimizes scatter, and improves image quality by restricting the beam.