4D ultrafast ultrasound imaging of naturally occurring shear waves in the human heart

TL;DR

This study introduces a 4D ultrafast ultrasound method to visualize and measure naturally occurring shear waves in the human heart, enabling more accurate 3D assessment of cardiac stiffness compared to traditional 2D techniques.

Contribution

The paper presents a novel 4D ultrafast ultrasound imaging technique for natural shear wave propagation in the human heart, improving 3D visualization and velocity measurement accuracy.

Findings

Successfully visualized shear wave propagation in the human heart.

Quantified shear wave velocities in different directions, revealing anisotropic propagation.

Demonstrated the feasibility of 4D ultrasound for comprehensive cardiac stiffness assessment.

Abstract

The objectives were to develop a novel three-dimensional technology for imaging naturally occurring shear wave (SW) propagation, demonstrate feasibility on human volunteers and quantify SW velocity in different propagation directions. Imaging of natural SWs generated by valve closures has emerged to obtain a direct measurement of cardiac stiffness. Recently, natural SW velocity was assessed in two dimensions on parasternal long axis view under the assumption of a propagation direction along the septum. However, in this approach the source localization and the complex three-dimensional propagation wave path was neglected making the speed estimation unreliable. High volume rate transthoracic acquisitions of the human left ventricle (1100 volume/s) was performed with a 4D ultrafast echocardiographic scanner. Four-dimensional tissue velocity cineloops enabled visualization of aortic and mitral valve closure waves. Energy and time of flight mapping allowed propagation path visualization and source localization, respectively. Velocities were quantified along different directions. Aortic and mitral valve closure SW velocities were assessed for the three volunteers with low standard deviation. Anisotropic propagation was also found suggesting the necessity of using a three-dimensional imaging approach. Different velocities were estimated for the three directions for the aortic (3.4$\pm$0.1 m/s, 3.5$\pm$0.3 m/s, 5.4$\pm$0.7 m/s) and the mitral (2.8$\pm$0.5 m/s, 2.9$\pm$0.3 m/s, 4.6$\pm$0.7 m/s) valve SWs. 4D ultrafast ultrasound alleviates the limitations of 2D ultrafast ultrasound for cardiac SW imaging based on natural SW propagations and enables a comprehensive measurement of cardiac stiffness. This technique could provide stiffness mapping of the left ventricle.