**3. Conclusion**

SWE is a newly developed diagnostic tool and is widely used in the musculoskeletal system.

SWE is a promising diagnostic modality for MSI and the accurate measurement of muscle and fascial tissues' properties, which has a major impact in clinical practice. In this chapter, diagnostic tools of magnetic resonance imaging, B mode ultrasound, and shear wave elastography in both acute and chronic phases are compared. There are pros and cons for utilization between the tools; however, there is new insight by using SWE in MSI not only properties of muscle but also fascial tissues. SWE generally evaluates tissue stiffness as viscoelasticity. SWE visualizes the propagation of shear waves and can quantify tissue "stiffness" by the speed of propagation. In the chronic MSI cases, viscoelasticity comes from ground substances, which are contained more in fascial tissue. The stiffness increases in fascial tissue more than muscle; therefore, in the chronic case of MSI, not only muscle but also a wide variety of connective tissues can be considered. However, utilization of SWE should be careful due to technical pitfalls or internal factors. All in all, SWE is a promising diagnostic modality for MSI and the accurate measurement of muscle and fascial tissues properties, which has a major impact in clinical practice. There are few studies that investigate for chronic musculoskeletal problem including fascial tissue problem by using SWE especially in clinical trials. Furthermore, the shear wave value is different according to active

muscle contraction. Therefore, further studies for chronic musculoskeletal problem will be expected in a wide variety of conditions.
