3-D high-frame-rate imaging of natural shear waves in the heart

Shear wave elastography images the heart using high-frame-rate ultrasound to detect mechanical waves traveling along the cardiac wall as a result of aortic and mitral valve closure. The propagation speed of these waves depends on myocardial stiffness, rendering shear wave elastography an interesting diagnostic tool for evaluating chamber compliance and diastolic filling properties. Traditionally, shear wave elastography has been studied in a 2-D parasternal view, and it remains unclear how the wave propagates in 3-D compared to the alignment of the 2-D imaging plane. Initial 3-D studies focused on shear wave elastography in the apical view, tracking a different component of tissue motion (longitudinal versus transverse) compared to the parasternal view. Therefore, this work deploys 3-D high-frame-rate imaging in six healthy volunteers (mean age of 31 ± 4.4 years) using the same echocardiographic view as currently used in 2-D. This allows to better understand the impact of excitation source location and wave propagation trajectories on wave speed estimation in 2-D. We will discuss the wave physics and cardiac mechanics underlying our results, considering recent advancements in the field. Additionally, we will present preliminary results in older healthy volunteers (>65 years) and patients with hypertrophic cardiomyopathy.