Equivalent spectra as a measure of beam quality.

The concept of the equivalent spectrum (Seq) is introduced, where Seq is defined as an idealized energy spectrum which results in identical attenuation properties as the actual spectrum of a given x-ray tube. Seq is described by two parameters, the equivalent aluminum filtration Aleq and the equivalent kilovoltage kVeq, which are evaluated iteratively using aluminum attenuation data. Published spectral data are used to demonstrate the merits of the equivalent spectrum technique, and experimental results are also presented. The technique is shown to be sensitive to changes in total filtration and, indirectly, to the waveform properties of the x-ray system. The use of the Seq may result in a better description of spectral properties for reporting purposes, and aid in standardizing radiographic techniques within an institution.