Encoded Multi-Line Transmissions for the Removal of Crosstalk Artifacts

Achieving higher frame rates in ultrasound imaging using traditional transmission methods often involves trade-offs, including reduced resolution and compromised signal-to-noise ratio (SNR). As a promising alternative, multi-line transmit (MLT) imaging has been introduced, where multiple focused beams are generated and insonified simultaneously in various directions, facilitating high frame rate data acquisition. Despite maintaining high SNR and spatial resolution, MLT is known to be susceptible to significant interference between the multiple beams, leading to crosstalk artifacts in the backscattered echoes and consequently degrading the overall image quality. The main objective of this study is to effectively remove these artifacts rather than merely suppressing them by employing spatiotemporal encoding techniques, thereby enhancing the image quality in high-frame rate ultrasound imaging. Specifically, we have presented two encoding methods for separating MLT beams: polarity-encoded MLT and delay-encoded MLT. Both encoding schemes are designed around a Hadamard matrix framework, with the former applying polarity apodization to the simultaneous beams and the latter implementing a zero or half-period time delay. The coding schemes were paired with a linear decoding process to eliminate crosstalk artifacts, and hence improving image quality without compromising the frame rate. We demonstrate that applying encoding schemes in combination with synthetic aperture focusing methods leads to significant improvements in resolution and overall coherence in the point target simulations and in vivo cardiac images, respectively.