3D Mechanical Wave Imaging for Myocardial Stiffness Assessment: Automation and measurements

Abstract

The propagation velocity of mechanical waves (MW) in the heart is directly related to the properties of the myocardium. Direct measurement of changes in the tissue properties provides a more accurate assessment of cardiac function and health than current measures, such as ejection fraction and strain imaging, and often require complex evaluation procedures involving multiple parameters. The study of complex, high-velocity propagation patterns of natural MW in the heart can be achieved using high-frame-rate (HFR) imaging in three dimensions, made possible by recent advancements in ultrasound technology. In this work, we utilized 3D HFR imaging to quantify the MW propagation velocity based on the time-of-flight of the MW propagation in 3D. First, we developed a robust methodology for automatically measuring 3D MW velocity, enabling both high-throughput and in-depth analysis. This further facilitated the development of a clinical tool in the future. Secondly, we assessed the validity of this pipeline through a method comparison (1D vs. 2D vs. 3D) and evaluated the impact of various parameters. Finally, the optimized pipeline was tested clinically on patients with aortic stenosis and acute myocardial infarction and healthy volunteers. 3D wave propagation exhibited complex patterns that varied significantly depending on the source of the MW. We showed that these complexities can lead to measurement inaccuracies in 1D/2D velocity estimation methods due to misalignment with the wave direction, whereas 3D estimation is robust against such errors. Moreover, without 3D visualization, measurement errors in 1D/2D may go undetected or be mistaken for pathology. Our results indicate that, while the developed pipeline remained stable under minor variations, the processing parameters affected the results. Finally, 3D MW velocities were consistent with common indices, such as the wall motion score index and ejection fraction, in patients with acute myocardial infarction. The 3D velocity map may also provide the potential to detect infarction areas, improving treatment planning—an aspect that requires further investigation in future studies.