Improving the Elevational Focusing of Fast Orthogonal Row-Column Electronic Scanning (FORCES) Ultrasound Imaging using Retrospective Transmit Beamforming (RTB)

Recent developments in Row Column Arrays (RCAs) have presented promising options for volumetric imaging without the need for the excessive channel counts of fully wired 2D-arrays. Bias programmable RCAs, also known as Top Orthogonal to Bottom Electrode (TOBE) Arrays, show further promise in that imaging schemes, such as Fast Orthogonal Row-Column Electronic Scanning (FORCES) allow for full transmit and receive focusing everywhere in the image plane. However, due to its fixed elevational focus and large transmit aperture, FORCES experiences poor elevational focusing away from the focal point. In this study we present a modification to the FORCES imaging scheme by applying Retrospective Transmit Beamforming (RTB) in the elevational direction to allow for elevational transmit focusing everywhere in the imaging plane. We evaluate FORCES and uFORCES methods, with and without RTB applied, when imaging both a cyst and wire phantom. With experiment we show improved elevational focusing capabilities away from the focal point when RTB is applied to both FORCES and uFORCES. At the focal point, performance with RTB remains comparable or improved relative to standard FORCES. This is quantified by the measurement of Full Width Half Max when imaging the wire phantom, and by the generalized Contrast to Noise Ratio when imaging the tubular cyst phantom. We also demonstrate the volumetric imaging capabilities of FORCES RTB with the wire phantom.