16 Harmonic Shear Wave Elastography

Heng Zhao

Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, USA

16.1 Introduction

As introduced in Chapter in this book, shear wave propagation speed can be used to noninvasively quantify tissue mechanical properties such as elasticity, which is an indicator of tissue health [1]. Unlike elastography/strain imaging using quasi‐static compression, which shows the contrast among materials with different stiffness [2], absolute elasticity/viscosity can be derived from the shear wave speed [1].

We need to introduce shear waves to the tissue in order to measure the propagation speed, which can be done either externally or internally. Internal sources include physiological movement such as heart beat, respiration, vocal cords vibration, etc., which are safe and do not involve additional devices [3]. However, shear waves generated by such sources are generally weak and lack control. Alternatively, the shear waves can be introduced using external sources. Ultrasound radiation force has been widely used for its capability of producing localized waves and evaluating the mechanical properties of a specified region, i.e. virtual biopsy [4, 5]. However, the motion in tissue generated by such a force is typically weak (amplitude of several micrometers) and subject to attenuation, phase aberration, and diffraction. Some methods such as supersonic shear imaging (SSI) [6] and comb‐push ultrasound shear elastography ...

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