Equivalent spectra as a measure of beam quality

The concept of the equivalent spectrum (S(eq)) is introduced, where S(eq) is defined as an idealized energy spectrum which results in identical attenuation properties as the actual spectrum of a given x-ray tube. S(eq) is described by two parameters, the equivalent aluminium filtration Al(eq) and the equivalent kilovoltage kV(eq), which are evaluated iteratively using aluminium 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 S(eq) may result in a better description of spectral properties for reporting purposes, and aid in standardizing radiographic techniques within an institution.