What is the purpose of beam collimation?

• A. To restrict the beam to the receptor size, reducing dose and improving image sharpness.
• B. To increase the beam size for larger fields.
• C. To increase the energy of photons.
• D. To lengthen exposure time while keeping dose constant.

Answer: (A)

Collimation limits the X-ray beam to the size of the receptor or the area of interest. By tightening the field, you irradiate less tissue, which lowers the patient’s radiation dose. It also reduces scatter that would otherwise reach the image receptor, leading to better image contrast and overall image quality. Collimation does not change photon energy (that’s set by the tube voltage and filtration) and it does not enlarge the beam or lengthen exposure time; those are controlled by other settings.