The useful beam refers to the part of radiation that passes through the opening in the beam-limiting device (aperture, diaphragm or collimator) and is used for imaging.

A stream of electromagnetic or particulate radiation that could be collimated and is generally unidirectional or divergent usually from a small source and restricted to a small-solid angle.

See also Ion Beam, Broad Beam, Useful Beam and Beam On Time.

Inherent filtration refers to a permanently implemented filter in the useful beam. Inherent filtration includes the window of the x-ray tube and any permanent enclosure for the tube or source.

Leakage radiation is all radiation escaping from within the source assembly except for the useful beam. It is primarily controlled through the design of the tube housing and proper collimator filtering.

The primary radiation is the useful beam emitted from the x-ray source.