Phase linear encoding in multi-line transmit imaging: Towards crosstalk artifact removal

Acquiring ultrasound images with high temporal resolution is essential for capturing motion in dynamic environments such as the heart. Conventional high-frame-rate approaches accelerate acquisition but often compromise image quality, reducing resolution, signal-to-noise ratio, and increasing motion artifacts. Multi-line transmit (MLT) imaging offers faster acquisition by generating multiple focused beams simultaneously. However, MLT images are degraded by crosstalk artifacts due to the interference between the simultaneous multiple beams. We introduce Multi-Line Transmit Incorporating Phase Linear Encoding with Synthetic Aperture decoding (MuLTIPLE-SA) to suppress crosstalk artifacts inherent to MLT, resulting in image quality comparable to that of standard single-line transmission (SLT) at accelerated acquisition rates. Our spatiotemporal encoding scheme uses Hadamard-based polarity or delay encoding across simultaneous beams. Synthetic aperture techniques are then used to combine multiple transmissions while decoding the echo signals to separate the contributions of each beam. MuLTIPLE-SA was evaluated in simulations, tissue-mimicking phantoms, and in vivo cardiac imaging. The combination of phase based encoding and synthetic aperture decoding reduced crosstalk artifacts, shown through reduced clutter and improved spatial coherence, and improved resolution due to synthetic focusing. Conventional MLT exhibited strong off-axis crosstalk, whereas MuLTIPLE-SA suppressed crosstalk by up to 27 dB on point targets, restoring image quality comparable to SLT while maintaining MLT's high frame-rate benefits. In a representative cardiac experiment, MuLTIPLE-SA improved generalized contrast-to-noise ratio (gCNR) in the right ventricle from 0.31 (conventional MLT) to 0.52, fully recovering SLT-level contrast by suppressing receive crosstalk. These findings demonstrate that MuLTIPLE-SA enables high temporal resolution without sacrificing image quality.