Scatterer localization technique for diverging-wave ultrasound acquisitions

Ultrasound localization microscopy (ULM) provides super-resolution images by tracking microbubbles (MBs) in small vessels, but current MB localization algorithms can be computational complex. In this work, we investigate an MB localization technique for diverging-wave transmit acquisition schemes using multiple receive apodizations. Field II and the MATLAB Ultrasound Toolbox were used to simulate a phased-array transducer (Verasonics P4-2v) transmitting diverging wavefronts steered at −5° and 5°, and pulse-echo data were obtained for point scatterers placed laterally at −3, 0, and 3 mm, and axially at 12 and 16 mm deep. Two even-function and two odd-function receive apodization profiles were applied to yield four beamformed IQ data frames for each point scatterer. An expression for a quadratic line, fit as a function of wavefront steering angle and scatterer range (distribution of local amplitude maxima/minima), and an expression for precise inter-pixel scatterer position along the line based on the pixel amplitudes from the four IQ data frames, were empirically derived. The technique was implemented and tested experimentally on a wire-target phantom, which showed good agreement with simulations (within 30 μm). These results show that super-resolution ULM images from diverging-wave acquisitions can be rapidly produced from beamformed IQ data.