Achieved with the placement of a lead diaphragm at the exit point of the tube head; restricts the X-ray beam to the desired size.

• A. Collimation
• B. Filtration
• C. Shielding
• D. Focusing

Answer: (A)

Collimation is the shaping and restricting of the X-ray beam to the size and shape needed for the exam. A lead diaphragm at the exit of the tube head serves as a collimator, creating an aperture that confines the beam to the field of interest. This concentrates the radiation where it’s needed, reduces patient dose, and decreases scatter to improve image quality. Filtration would remove low-energy photons from the beam but doesn’t change its size. Shielding blocks radiation from reaching areas not being imaged, and focusing concerns the geometric alignment of the beam with the receptor rather than its size.