Quantitative assessment of regional myocardial stiffness and anisotropy using 3D Shear Wave Elastography

Background/Introduction Myocardial stiffness is a crucial indicator of cardiac biomechanics and diastolic function. Its assessment is complicated by the myocardium's complex 3D fiber architecture and the resulting anisotropic mechanical behavior. Current 2D shear wave elastography (SWE) measures stiffness in an indeterminate direction relative to fiber orientation, leading to variability and diagnostic uncertainty. We introduce a novel clinical modality based on real-time 3D-SWE to quantitatively assess diastolic stiffness in complex anisotropic tissue, aiming to demonstrate its feasibility in healthy volunteers (HVs). Methods A custom ultrasound system for 3D-SWE was developed using a matrix transducer. It remotely generates a shear wave via the acoustic radiation force and tracks its 3D propagation using ultrafast volumetric imaging (3,000 volumes/s) (Fig A). ). Shear wave velocity (SWV) is measured within a 10x16x16 mm³ myocardial volume, where the long axis of the SWV profile directly quantifies stiffness along the myocardial fibers. In vivo acquisitions were ECG-triggered during diastole and guided by real-time 2D B-mode imaging. Following standard validation on calibrated phantoms against a commercial 2D-SWE system, an in vivo study was conducted on 10 HVs (age 32±8 years). Measurements targeted the basal anteroseptal (AS) segment, the RV free wall in the parasternal long-axis and short axis view and the apex in apical view. Results Phantom validation demonstrated high accuracy and reliability (R² = 0.95, standard deviation = 5.20%). In vivo, 3D shear wave propagation was successfully observed and tracked in all 10 HVs and all the targeted myocardial segments. Analysis of the anisotropic, elliptical velocity profile at the mid-wall level yielded robust quantitative measurements. The median SWV along the myocardial fibers in the AS segment was 1.74 m/s (interquartile range: 1.59–1.90 m/s). The modality showed excellent reproducibility, with an intra-individual variability of 4.66% across five repeated acquisitions per subject. Conclusion Real-time 3D-SWE is a feasible and highly reproducible novel modality for the quantitative assessment of myocardial stiffness in humans. By overcoming the directional limitations of 2D-SWE, this technique enables accurate, fiber-specific stiffness evaluation, paving the way for improved non-invasive diagnostics in cardiomyopathies and diastolic dysfunction.3D SWE Technology