What is the function of the collimator?

• A. Increase beam intensity
• B. Narrow the beam to the area of interest
• C. Focus electrons onto the anode
• D. Filter out low-energy photons

Answer: (B)

The function being tested is how the beam is shaped to match the area you intend to image. A collimator narrows the X-ray beam to the size and shape of the receptor or region of interest. By limiting the beam, fewer tissues are exposed, scatter is reduced, and image quality and contrast are improved because there’s less off-target radiation and fuzz around the edges.

Increasing beam intensity isn’t the collimator’s job—exposure factors control that. Focusing electrons onto the anode happens in the tube’s electron optics, not in the collimator. Filtering out low-energy photons is done by the filtration materials (like aluminum) placed in the beam path, not by the collimator.