The collimator is best described as what?

• A. A lead disc with a round or rectangular hole in the center placed between the X-ray tube and the cone
• B. A large copper disk to conduct heat
• C. A transparent plastic guide
• D. A secondary source of X-rays

Answer: (A)

A collimator is a device that shapes and confines the X-ray beam to the size of the area of interest, which reduces patient exposure and improves image quality by limiting scatter. The best description is a lead disk with a round or rectangular hole in the center, placed between the X-ray tube and the cone. The lead blocks off-axis radiation so only the defined aperture forms the beam. The other options don’t fit because a copper disk is for heat management, a transparent plastic guide isn’t a beam-limiting device, and a collimator does not emit X-rays.