Ultrasound imaging using transmit wavefront synthesis: Spatial and frequency diversity approach to compounding

We have developed a modern array driver employing multi-channel arbitrary waveform generator and linear amplifiers for transmit wavefront synthesis. The system utilizes deep waveform memory that can be configured for switching between transmit patterns seamlessly thus allowing for the use of spatial and frequency diversity in image acquisition. In this paper, we present the first experimental results demonstrating dramatic reduction in sidelobe artifacts as well speckle reduction. Using a 3.5 MHz, 32-element concave array with 40-mm radius of curvature designed for dual-mode operation of therapy and imaging, Single Transmit Focus (STF) and Multiple Transmit Focus (MTF) patterns with varying spatial and frequency characteristics provided a reduction of these artifacts and greater source separation near the focus. Multiple embedded wire-target tissue mimicking phantoms and single leech ganglions in a saline bath were used as imaging targets to test sidelobe reduction; each with Synthetic Aperture (SA) imaging as a validation. Beamformed echo data was incoherently and coherently compounded to achieve sidelobe and incoherent speckle reduction.