Ultrasound Elastography for Biomedical Applications and Medicine

13 Viscoelastic Creep Imaging

Carolina Amador Carrascal

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

13.1 Introduction

Elasticity imaging is an emerging imaging approach that uses the elasticity of tissue as the contrast mechanism in images. Elasticity or stiffness is a physical property of a material that returns to its original shape after the stress (e.g. external force) that made it deform is removed. The mathematical description of such property is known as elastic modulus or modulus of elasticity. It has been shown that the elastic modulus of tissues in the body can vary over 6 orders of magnitude, making the dynamic range of this contrast mechanism quite large [1]. Moreover, it is established that soft biological tissue exhibits viscoelastic behavior [2].

Viscoelastic materials exhibit both elastic and viscous behavior characterized by being time or frequency dependent. Measuring tissue viscoelasticity is important because:

1. if the mechanical properties of a viscoelastic material are characterized only from its elasticity, the elasticity measurement can be biased higher than the actual value [3];
2. besides the advantages of dynamic range in elastic modulus of tissue, measuring tissue viscosity complements the diagnostic capability of elasticity imaging; for instance a study has showed better discrimination between malignant and benign tumors when measuring the time‐varying viscous response of breast to a small deforming ...