Shear wave elastography in MSK

Abstract

Objectives To describe our experience applying shear wave elastography to the musculoskeletal system, as well as some potential sources of artifact when applying this new technology. Summary Disease states in the musculoskeletal system often manifest as altered tissue morphology evident on conventional gray-scale ultrasound imaging. These states also display other changes, such as altered tissue vascularity and mechanical properties. An example would be the tendon softening associated with tendinosis. US elastography provides a measure of local soft-tissue stiffness by means of mechanical stimulation. Presently, the two most common forms of US elastography measure tissue stiffness and strain by recording (a) how tissues respond to external compression obtained by applying manual pressure (Quasi-static or compression based on response to acoustic radiation force generated by the ultrasound transducer, the latter referred to as Shear-Wave Elastography (SWE). SWE employs a focused acoustic beam generated by the US transducer to compress the underlying tissue, thereby inducing a local shear wave. The speed of that wave, also known as the shear- wave velocity (SWV), is then measured as it propagates through the tissue and displayed as a parametric image or through selective region-of-interest (ROI) analysis, measured in meters per second. SWV provides a quantitative metric of tissue stiffness because it directly relates to the local shear elastic modulus, such that the stiffer the tissue, the greater the SWV. Consequently, some vendors directly display shear wave data as elastic modulus in kilopascals (KPS). In the current discussion, we briefly review some basic principles of shear wave imaging, review some of the common musculoskeletal applications, to date, and describe our experience using SWE in the musculoskeletal system with attention to skeletal muscle and tendons. We review some potential artifacts that the sonographer should be aware of in applying this new technology to tendon and muscle imaging.