Superharmonic Imaging with Plane Wave Beamforming Techniques

Superharmonic imaging (SpHI) using dual-frequency (DF) transducers enables high-contrast microvasculature imaging while suppressing tissue clutter. It takes advantage of the high-frequency components within the nonlinear response of microbubble contrast agents when excited with a low-frequency pulse. SpHI has been demonstrated with array-based DF transducers with traditional line-by-line imaging schemes where the acquisition frame rate is limited by the number of image lines needed over the imaging field-of-view. In this work, we implement plane wave imaging approaches on programmable systems and investigate the image acquisition frame rate and image quality of SpHI in vitro and in vivo, using an integrated DF probe comprising a 21 MHz (high-frequency; 256 elements) array stacked on a 2 MHz (low-frequency; 32 elements) array. Micro-ultrasound imaging with high-frequency plane wave transmission at 25 steering angles and coherent compounding on receive was demonstrated in vivo, which showed good image contrast and resolution compared to traditional line-by-line imaging, while achieving an acquisition frame rate of 158 Hz. The 5-angle coherently compounded in vitro SpHI images showed ~4 dB improvement in tissue clutter suppression compared to images reconstructed from 0° steering. With 5-angle compounding, the acquisition frame rate in SpHI reached 588 Hz for a 30 mm imaging depth, moving SpHI towards 2D real-time imaging.