beam collimation, 1. the restriction of the size and shape of the x-ray beam to the area being examined or treated by confining the beam with metal diaphragms or shutters with high radiation-absorption power. See beam restrictor. 2. (in dentistry) a beam-restricting device with either a round or rectangular opening. According to federal regulations, the round collimator reduces the diameter of the x-ray beam to no more than 2.75 inches as it exits the tubehead.
