title: Methods for using 3-D ultrasound speckle tracking in biaxial mechanical testing of biological tissue samples.
abstract: Being multilayered and anisotropic, biological tissues such as cardiac and arterial walls are structurally complex, making the full assessment and understanding of their mechanical behavior challenging. Current standard mechanical testing uses surface markers to track tissue deformations and does not provide deformation data below the surface. In the study described here, we found that combining mechanical testing with 3-D ultrasound speckle tracking could overcome this limitation. Rat myocardium was tested with a biaxial tester and was concurrently scanned with high-frequency ultrasound in three dimensions. The strain energy function was computed from stresses and strains using an iterative non-linear curve-fitting algorithm. Because the strain energy function consists of terms for the base matrix and for embedded fibers, spatially varying fiber orientation was also computed by curve fitting. Using finite-element simulations, we first validated the accuracy of the non-linear curve-fitting algorithm. Next, we compared experimentally measured rat myocardium strain energy function values with those in the literature and found a matching order of magnitude. Finally, we retained samples after the experiments for fiber orientation quantification using histology and found that the results satisfactorily matched those computed in the experiments. We conclude that 3-D ultrasound speckle tracking can be a useful addition to traditional mechanical testing of biological tissues and may provide the benefit of enabling fiber orientation computation.
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; Department of Biomedical Engineering, National University of Singapore, Singapore.
authors.forename: Choon Hwai
authors.initials: CH
authors.lastname: Yap
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Dae Woo
authors.initials: DW
authors.lastname: Park
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Debaditya
authors.initials: D
authors.lastname: Dutta
authors.affiliation: Heart and Vascular Institute, University of Pittsburgh Medical Center (UPMC), Pittsburgh, Pennsylvania, USA; Department of Bioengineering, University of Pittsburgh School of Engineering, Pittsburgh, Pennsylvania, USA.
authors.forename: Marc
authors.initials: M
authors.lastname: Simon
authors.affiliation: Center for Ultrasound Molecular Imaging and Therapeutics, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; Heart and Vascular Institute, University of Pittsburgh Medical Center (UPMC), Pittsburgh, Pennsylvania, USA; Department of Bioengineering, University of Pittsburgh School of Engineering, Pittsburgh, Pennsylvania, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, USA. Electronic address: Kangkim@upmc.edu.
authors.forename: Kang
authors.initials: K
authors.lastname: Kim
mesh_terms: D000465:Algorithms; D000818:Animals; D001696:Biomechanical Phenomena; D019560:Echocardiography, Three-Dimensional / Q000379:methods*; D051381:Rats; D013314:Stress, Mechanical
keywords: 3-D ultrasound speckle tracking; Biaxial mechanical testing; Constitutive relations; Soft tissue mechanics