Ultrasound Elastography for Biomedical Applications and Medicine

9 Wave Propagation in Viscoelastic Materials

Yue Wang¹ and Michael F. Insana²

¹ Department of Bioengineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana‐Champaign, Champaign, IL, USA

² Departments of Bioengineering and Electrical and Computer Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana‐Champaign, Champaign, IL, USA

9.1 Introduction

Utilizing dynamic‐wave elastographic techniques for estimating mechanical properties of tissue offers several advantages. Firstly, among the many methods now available for visualizing tissue viscoelastic properties, wave‐based techniques are valued for their ability to quantitatively map shear modulus G. The shear moduli of human tissue can span six orders of magnitude, from a few hundred Pa for brain tissue to several GPa for bone and cartilage. Also, the shear moduli of diseased tissues can increase 2–10‐fold when compared to healthy baseline values [1–3]. High elasticity contrast for disease states is beneficial in clinical diagnosis but can pose challenges when estimating properties. Secondly, unlike static compression elastography, dynamic methods apply stress or strain locally with adjustable frequency in wave‐based techniques, thus estimation bias concerns from stress distributions and boundary conditions outside of the region of interest are reduced. Ultrasound and other phase‐sensitive imaging modalities (MRI, optical coherence ...