What device is used to control the size and shape of the primary x-ray beam?

• A. Collimator
• B. Lead apron
• C. Filter
• D. Receptor

Answer: (A)

Controlling the size and shape of the primary x-ray beam is achieved with a collimator. This device attaches to the x-ray tube head and uses a lead shielding plate with adjustable openings to define the beam’s dimensions, typically producing circular or rectangular fields. By limiting the irradiated area, the collimator reduces patient and operator exposure and decreases scatter, which helps improve image contrast and clarity. The other options don’t shape the beam: a lead apron protects tissues from scatter but doesn’t define the beam; a filter removes low-energy photons to lower dose without changing beam size; and the receptor is what captures the image, not something that shapes the beam.