Finite beam-width ray model for geometric spectral broadening

The purpose of the study was to compare measured spectral width and maximum frequency with that predicted from ray models of geometric spectral broadening. Zero and finite beam-width models were used. Spectral data were acquired from a string phantom using two commonly-used linear array systems. Beam width and Doppler aperture sizes were measured using a needle hydrophone. The results showed that the experimentally measured data agreed best with the finite beam-width model. The zero beam-width model was in error by up to 50% for calculated spectral width, and up to 10% for maximum frequency. It is concluded that spectral width and maximum frequency are best calculated using the finite beam-width model, and that ultrasound manufacturers could improve the variation in spectral broadening measured at different locations on a single machine by adjusting the aperture size to give a constant subtended angle and beam width.