Measurement of anisotropic mechanical properties in porcine brain white matter ex vivo using magnetic resonance elastography
| Autor: | Dennis J. Tweten, Joel R. Garbow, John L. Schmidt, Ruth J. Okamoto, Andrew Badachhape, Alex J. Reiter, Philip V. Bayly |
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| Rok vydání: | 2018 |
| Předmět: |
Shear waves
Materials science Swine Biomedical Engineering Article 030218 nuclear medicine & medical imaging Biomaterials Shear modulus 03 medical and health sciences 0302 clinical medicine Nuclear magnetic resonance Transverse isotropy Ultimate tensile strength Animals Anisotropy Isotropy Brain Models Theoretical Magnetic Resonance Imaging White Matter Magnetic resonance elastography Shear (sheet metal) Mechanics of Materials Elasticity Imaging Techniques 030217 neurology & neurosurgery |
| Zdroj: | Journal of the Mechanical Behavior of Biomedical Materials. 79:30-37 |
| ISSN: | 1751-6161 |
| Popis: | The mechanical properties of brain tissue, particularly those of white matter (WM), need to be characterized accurately for use in finite element (FE) models of brain biomechanics and traumatic brain injury (TBI). Magnetic resonance elastography (MRE) is a powerful tool for non-invasive estimation of the mechanical properties of soft tissues. While several studies involving direct mechanical tests of brain tissue have shown mechanical anisotropy, most MRE studies of brain tissue assume an isotropic model. In this study, an incompressible transversely isotropic (TI) material model parameterized by minimum shear modulus (μ(2)), shear anisotropy parameter (ϕ), and tensile anisotropy parameter (ζ) is applied to analyze MRE measurements of ex vivo porcine white matter (WM) brain tissue. To characterize shear anisotropy, “slow” (pure transverse) shear waves were propagated at 100, 200 and 300Hz through sections of ex vivo brain tissue including both WM and grey matter (GM). Shear waves were found to propagate with elliptical fronts, consistent with TI material behavior. Shear wave fields were also analyzed within regions of interest (ROI) to find local shear wavelengths parallel and perpendicular to fiber orientation. FE simulations of a TI material with a range of plausible shear modulus (μ(2)) and shear anisotropy parameters (ϕ) were run and the results were analyzed in the same fashion as the experimental case. Parameters of the FE simulations which most closely matched each experiment were taken to represent the mechanical properties of that particular sample. Using this approach, WM in the ex vivo porcine brain was found to be mildly anisotropic in shear with estimates of minimum shear modulus (actuation frequencies listed in parenthesis): μ(2) = 1.04 ± 0.12 kPa (at 100 Hz), μ(2) = 1.94 ± 0.29 kPa (at 200 Hz), and μ(2) = 2.88 ± 0.34 kPa (at 300 Hz) and corresponding shear anisotropy factors of ϕ = 0.27 ± 0.09 (at 100 Hz), ϕ = 0.29 ± 0.14 (at 200 Hz) and ϕ = 0.34 ± 0.13 (at 300 Hz). Future MRE studies will focus on tensile anisotropy, which will require both slow and fast shear waves for accurate estimation. |
| Databáze: | OpenAIRE |
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