Ultrasound Elastography for Biomedical Applications and Medicine

7 Transverse Wave Propagation in Bounded Media

Javier Brum

Laboratorio deAcustica Ultrasonora, Instituto de Fisica, Facultad de Ciencias, Universidad de la Republica, Montevideo, Uruguay

7.1 Introduction

Wave propagation in bounded media has been widely used in several fields (e.g. non‐destructive evaluation, seismology, underwater acoustics) to determine different material properties. Recently, ultrasound elastography, motivated by several medical applications, has used guided waves to determine, non‐invasively, the mechanical properties of plate‐like tissue, such as cornea, skin, myocardium, bladder, arteries, and tendons [1–10]. In these applications, the shear wavelength (λ ∼ 1–10 cm) is comparable to the tissue's thickness (e.g. ∼0.1 cm for arteries and skin, ∼1 cm for myocardium). As a consequence, the shear wave is guided within the tissue due to the successive reflections on the tissue boundaries. In this scenario, the relation between wave speed and elasticity is more complex than in the case of an infinite tissue, where the shear waves propagate in the bulk of the sample (i.e. away from the boundaries). To retrieve the bulk shear wave speed and therefore the shear elasticity of the plate‐like tissue, the typical sequence is the following:

• first waves are generated inside the plate
• then the transverse component of the displacement field is acquired by ...