Reconstruction of shear wave speed in layered media using time-harmonic excitation and pulse-echo imaging

Abstract

Recent advances in high-frequency ultrasound imaging have opened new possibilities for quantitative characterization of skin properties. Noninvasive, accurate measurements of elasticity for multiple layers (e.g., stratum corneum, epidermis, dermis) are potentially beneficial for development and validation of new skin treatments. Here, pulse-echo ultrasound imaging using linear arrays is used to measure time-harmonic tissue displacements induced by a mechanical shaker. It is shown that reconstruction of time-harmonic displacement amplitude and phase in induced elastic waves is feasible for frame rates exceeding the Nyquist frequency and for echoes acquired using multiple transmits per frame. Measured wavefields are inverted using spatial Fourier analysis, numerical solution of the Helmholtz equation by finite difference methods, and direct observation of shear wavelengths. These approaches are validated using a 5 MHz diagnostic imaging array with a clinical scanner (Zonare z.one, L8-1 array) and multlilayered phantoms with varying elastic properties and echogenicity. Further verification of these methods is performed by comparing with finite-element simulations employing a linear elasticity model. Feasibility for measurement of skin layer elastic properties using high-frequency ultrasonic imaging is demonstrated using a 50 MHz linear array and a small-animal scanner (Vevo 2100, MS700 array) for measurements on porcine skin.Recent advances in high-frequency ultrasound imaging have opened new possibilities for quantitative characterization of skin properties. Noninvasive, accurate measurements of elasticity for multiple layers (e.g., stratum corneum, epidermis, dermis) are potentially beneficial for development and validation of new skin treatments. Here, pulse-echo ultrasound imaging using linear arrays is used to measure time-harmonic tissue displacements induced by a mechanical shaker. It is shown that reconstruction of time-harmonic displacement amplitude and phase in induced elastic waves is feasible for frame rates exceeding the Nyquist frequency and for echoes acquired using multiple transmits per frame. Measured wavefields are inverted using spatial Fourier analysis, numerical solution of the Helmholtz equation by finite difference methods, and direct observation of shear wavelengths. These approaches are validated using a 5 MHz diagnostic imaging array with a clinical scanner (Zonare z.one, L8-1 array) and multlilaye...