Positive beam limitation is a safety feature that ensures the size of the x-ray field is no larger than the

• A. collimator opening
• B. source-to-image distance
• C. detector dimensions
• D. patient skin

Answer: (C)

Positive beam limitation is about making the x-ray field fit the size of the image receptor. The detector dimensions determine the maximum area that needs to be irradiated—the field is restricted to match the detector so you don’t expose tissue outside what will be captured, which helps control patient dose and image quality. The distance from the source to the image receptor affects magnification and geometry, but it doesn’t set the field size itself. The collimator helps shape the light field, but the safety limit is the detector size, so the field cannot be larger than the detector.