Methods for Using 3-D Ultrasound Speckle Tracking in Biaxial Mechanical Testing of Biological Tissue Samples

This study introduced and validated a novel experimental framework combining planar biaxial mechanical testing with three-dimensional ultrasound speckle tracking to characterize the mechanical behavior and fiber architecture of biological soft tissues. Rat left ventricular myocardium was subjected to quasi-static biaxial loading while volumetric ultrasound imaging captured full-field three-dimensional strain distributions. A nonlinear curve-fitting algorithm was used to compute strain energy function parameters and spatially varying fiber orientations, which were validated against finite-element simulations and histological measurements. The results demonstrated that this combined approach can accurately quantify myocardial anisotropy, stiffness, and transmural fiber organization beyond surface-based mechanical testing methods.