28 Model‐free Techniques for Estimating Tissue Viscoelasticity

Daniel Escobar, Luiz Vasconcelos, Carolina Amador Carrascal and Ivan Nenadic

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

28.1 Introduction

Current shear wave imaging techniques are useful to identify tissue linear viscoelastic properties; however, to quantify these properties a rheological model must be used. This chapter reviews current methods that have been proposed to quantify viscoelastic properties in a model‐independent way. Two methods, called acoustic radiation force‐induced creep (RFIC) and acoustic radiation force‐induced creep–recovery (RFICR), estimate complex elastic modulus from time‐dependent creep response or creep–recovery response induced by acoustic radiation force in combination with acoustic radiation force shear wave propagation [13]. A third model‐free method named AMUSE (attenuation measuring ultrasound shearwave elastography), estimates shear wave velocity and attenuation independently. AMUSE measures the location and shape of the k‐space magnitude maxima that is directly related to the speed and attenuation of the shear wave propagating in the tissue [4]. Measuring both the shear wave velocity and attenuation at given frequencies characterizes tissue mechanical properties and allows a true measurement of tissue viscoelasticity. It is important to note that all the models here described consider a source‐free, harmonic shear wave propagating ...

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