Abstract
Tissues of the brain, especially white matter, are extremely heterogeneous—with constitutive responses varying spatially. In this paper, we implement a high-resolution Finite Element (FE) head model where heterogeneities of white matter structures are introduced through Magnetic Resonance Elastography (MRE) experiments. Displacement of white matter under shear wave excitation is captured and the material properties determined through an inversion algorithm are incorporated in the FE model via a two-term Ogden hyper-elastic material model. This approach is found to improve model predictions when compared to experimental results. In the first place, mechanical response in the cerebrum near stiff structures such as the corpus callosum and corona radiata are markedly different compared with a homogenized material model. Additionally, the heterogeneities introduce additional attenuation of the shear wave due to wave scattering within the cerebrum.
Highlights
With approximately 2.8 million cases reported annually in the United States [1], traumatic brain injury (TBI)—commonly caused by a direct blow or impulse to the head—remains a pressing concern for study
We introduce a heterogeneous material description of white matter structures to our high-resolution Finite Element (FE) model to account for the local differences in mechanical response between different regions of the brain
The FE method is commonly used to determine the mechanical response of brain tissue in order to develop improved diagnostic tools and protective measures to reduce the prevalence of TBI
Summary
With approximately 2.8 million cases reported annually in the United States [1], traumatic brain injury (TBI)—commonly caused by a direct blow or impulse to the head—remains a pressing concern for study. A very useful tool to measure heterogeneity in-vivo is the Magnetic Resonance Elastography (MRE) [11], where local mechanical properties of brain tissue are quantitatively determined by external actuation of the head to generate shear waves. This technique has been successfully applied to a variety of different applications: investigating decreases in whole-brain stiffness with age [12] and in neurodegenerative diseases [13]; measurement of tumor stiffness [14]; and as a marker for TBI severity [15]. To the best of our knowledge, this is the first attempt to include heterogeneity of brain tissue via MRE in a high-resolution FE model
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