Synthetic Aperture Flow Imaging Using a Dual Stage Beamformer Approach

Synthetic aperture flow estimation has several advantages compared to the conventional flow estimation however this requires a high number of calculations. A dual beamformer approach is proposed to lower the number of calculations and maintain a beamforming quality sufficient for flow estimation. This approach contains a two-stage procedure using two different beamformers. The first stage beamformer has a single focal point in both transmit and receive. The fully dynamic second beamformer uses the data from the first stage to beamform the image. Focal points in the first beamformer are considered as virtual sources in the second beamformation algorithm. High resolution image lines are generated by the second stage beamformation. Four emissions in each emission sequence repeat over time. The velocity is estimated by cross correlating high resolution lines which is a function of depth. The cross correlation functions are averaged over 16 high resolution image pairs to improve the better estimates. Varying interspaces [2, 6, 10, 14] resulted in the standard deviation and the bias B of the axial velocity were [1.92, 2.0, 2.07, 2.21] % and [0.61, 1.07, 1.29, 1.5] % compared to the peak velocity respectively. The parameter study showed that larger interspaces gave an increased standard deviation and the bias. Furthermore more emissions in averaging gave better performance. The performance of the simulation indicates that this dual beamformer approach is able to estimate the flow velocity. Interspaces between emissions and number of emission sets in averaging have an influence on the estimation.