Myocardial shear wave imaging(SWI)
SWI is a technique based on ultrasonic mechanical effect, which can be used to evaluate the hardness of soft tissue noninvasively and quantitatively. In the past ten years, it has been used in breast, liver and other diseases, and has certain clinical value. SWI uses the propagation characteristics of shear waves and the speed of wave transmission to estimate the stiffness of the tissue. Shear waves can be induced naturally in the heart when the atrioventricular or ventricular artery valves are closed, but they can also be induced mechanically using an external source. In fact, SWI has been shown to be significantly positively correlated with age, end-diastolic wall thickness, loading status (left atrial size, LVEDP), and MRI cardiac-related fibrosis indicators in healthy volunteers and in some patients with disease(59-63). However, the accuracy of the technique is greatly challenged by the operator’s technique, the particular geometry, viscosity, anisotropy, contraction and diastole of the heart, haemodynamics and pathology that will affect the shear wave generation and wave speed.(64) In addition to this, due to the limitations of ultrasound views and sites, the shear waves assessed only reflect local myocardial stiffness and do not reflect the overall level of myocardial stiffness. With this in mind, there is an urgent need for consistent data collection and reporting as the number of clinical studies of cardiac SWI continues to increase. In a recent review, Caenen A, et al.(64) made some constructive suggestions to improve the accuracy of SWI and to facilitate the comparison of SWE results between studies.