Transit time broadening: a pulsed Doppler ultrasound perspective

Many studies on transit time broadening have been performed to characterize its effect on the Doppler spectrum. However, the dependence of transit time broadening on an important pulsed Doppler ultrasound parameter - the range gate used for depth localization - has not been rigorously addressed. The purpose of this paper is to provide an analysis of how the range gate may contribute to transit time broadening from a pulsed Doppler perspective. Our analysis and simulation results show that the range gate can contribute to transit time broadening at small beam-flow angles. In particular, at such angles, the spectral broadening bandwidth is dependent on the effective axial length of the sample volume. On the other hand, at higher beam-flow angles, the spectral broadening bandwidth is dependent on ultrasound beam parameters such as local length and aperture size: a finding that is consistent with previous studies. Our analysis also shows that there exists a transition beam-flow angle at which the parameters governing transit time broadening undergo a significant change.