Introduction

The mechanical properties of many materials have been known in detail for hundreds of years, whereas those of biological tissues have been largely unknown until only recently. In medicine, the evaluation of the mechanical properties of tissues was limited to subjective palpation of superficial structures, and elastic properties of deeper tissues could only be evaluated during surgery. The mechanical properties of soft tissues are related to the cellular and extracellular components, structural organization of various elements, function, physiological factors such as blood flow and pathological conditions that affect these tissues. Elasticity of tissues cannot be directly assessed by existing conventional imaging techniques such as CT, MRI, nuclear medicine, and ultrasound. The advent of quantitative elastography technology in medicine offers new opportunities. Quantitative elastography techniques typically utilizes a source of mechanical waves and an imaging technology to assess the propagation of these waves. The availability of practical noninvasive elastography techniques for quantifying tissue stiffness and increased awareness of mechanical property changes that occur in pathological conditions has generated interest among researchers and physicians to understand and apply tissue mechanical properties for clinical use. This interest has grown dramatically over the last two decades, resulting in thousands of publications in the field of elastography. These emerging diagnostic technologies are growing dramatically in their impact on clinical medicine and their contribution to science.