A stochastic approach to delays optimization for narrowband transmit beam pattern in medical ultrasound

Abstract In ultrasound imaging, state-of-the-art methods for Transmit Beam Pattern (TBP) optimization have well-known drawbacks like non-uniform beam width over depth, significant side lobes, and quick energy drop-out beyond the focal region. To overcome these limitations, we develop a TBP optimization approach by focusing on its narrowband approximation and considering transmit delays as free variables instead of linked to specific focal depths. We formulate a non-linear Least Squares problem to minimize the difference between the TBP corresponding to a set of delays and the desired one, modeled as a 2D rectangle elongated along the beam axis. Three metrics are defined to quantitatively evaluate the results. Results obtained by synthetic simulations show that the main lobe width is considerably more intense and uniform over the whole depth range compared to classical focalized Beam Patterns. The application of the method to elastogra-phy shows improvements in the ultrasound energy concentration along a desired axis.