Ultrasound measurement of fiber orientation and tissue strain in excised myocardium under biaxial tension

Abstract

Biaxial mechanical testing is a useful tool for determining the mechanical properties of myocardium tissues, which are anisotropic due to their layered and fibrous microstructure. Mechanical properties of the tissue are largely determined by those of the laminar myofiber sheets, whose orientations vary in a helix throughout the tissue thickness. Fiber architecture of tested tissues is usually determined post hoc by destructive histological sectioning, and the contribution of fiber kinematics to tissue-level mechanical behavior is accomplished by assuming a continuum model for the myocardium. In this work is presented simultaneous ultrasound-based measurement of fiber orientation and tissue strain in excised myocardium under biaxial tension. Two-protocol (1:1 and 1:6) testing is employed in order to probe tissue anisotropy and fiber kinematics. An ultrasound linear array (15 MHz) is scanned by rotation about the imaging axis to obtain three-dimensional backscatter data from the tissue during quasi-static biaxial deformation, from which transmural fiber orientation and tissue strain are determined by backscatter tensor imaging and 3D speckle tracking, respectively. Results illustrate feasibility of the simultaneous measurement and future utility for studying fiber mechanics in diseased tissues. Fiber rotation and elongation measured directly from ultrasound is compared to that calculated under the continuum assumption.