Multi-resolution transverse oscillation in ultrasound imaging for motion estimation.

Beyond all recent methods for estimating multidimensional motion vectors in ultrasound (US) image sequences, the transverse oscillation (TO) images coupled with a phase-based motion estimator has shown to be an extremely promising approach. To improve existing TO techniques, this paper proposes a multi-resolution transverse oscillation (MRTO) that measures the motion in US image sequences at different resolutions. Several TO images are created using harmonic images obtained from nonlinear US propagation or from composite emissions. Motion estimations are made with increasing resolution levels, i.e., decreasing transverse wavelength, to improve the previous measurements. When only lateral motion is applied to the tissue, the resulting estimations, quantitatively assessed in both simulations and in vitro experiments, are significantly improved in terms of mean motion error and standard deviation. With a 1-mm displacement in the chirp transmission, the error is reduced from 40.9% to 0.1% in the simulation and from 41.6% to 1.5% in the experiment. The first quasi-static elastography results, in simulation and experimentation, also confirm this improvement with an increased contrast-to-noise ratio and signal-to-noise ratio.