Plane wave approaches with dual-frequency arrays for superharmonic contrast imaging

Abstract

Superharmonic imaging (SpHI) using dual-frequency probes enables high-contrast microvasculature imaging by taking advantage of higher order harmonics of the broadband nonlinear response from microbubble (MB) contrast agents. We previously introduced a DF probe with a low-frequency (LF, 2 MHz; 32 elements) array behind a high-frequency (HF, 21 MHz; 256 elements) array and demonstrated SpHI with conventional walking-aperture approaches which limit acquisition rates. In this work, ultrafast imaging is investigated to overcome this challenge. We demonstrate SpHI with plane waves and coherent compounding in vitro and in vivo while evaluating acquisition frame rates. LF plane waves were implemented on VevoF2 systems (FUJIFILM Visualsonics, Toronto) with beam steering enabled by element-specific delays (9 angles between ±10°, step: 2.5°). All SpHI images showed almost complete suppression of tissue clutter to the background noise level. A 2.5 dB contrast improvement was found in vitro with coherent compounding . Tumor perfusion and fine vascular structures were visualized in vivo. SpHI acquisition frame rate reached 3.5 kHz at 0° and 396 Hz with 9 angles, ∼40 times that of walking-aperture approaches. These results demonstrate plane wave imaging approaches can increase SpHI frame rates while maintaining a high image contrast for visualizing vasculature, enabling SpHI for fast flow imaging.