What forms the shape and size of the x-ray beam as it leaves the tube head?

• A. Anode
• B. Filament
• C. Collimator
• D. Glass envelope

Answer: (C)

Collimation controls the size and shape of the x-ray beam as it leaves the tube head. The collimator is the device inside the tube head that defines the beam’s aperture, giving the exit field a specific shape (often rectangular or circular) and a limited size to match the image receptor. This shaping reduces patient exposure by limiting unnecessary radiation and helps ensure the beam covers only the area of interest on the receptor. The other components—filament (which produces electrons), anode (the target that generates x-rays when struck by electrons), and the glass envelope (which houses and protects the tube in vacuum)—do not determine the beam’s geometry.