An anatomically detailed and personalizable head injury model: Significance of brain and white matter tract morphological variability on strain

Abstract

Finite element head (FE) models are important numerical tools to study head injuries and develop protection systems. The generation of anatomically accurate and subject-specific head models with conforming hexahedral meshes remains a significant challenge. The focus of this study is to present two developmental works: first, an anatomically detailed FE head model with conforming hexahedral meshes that has smooth interfaces between the brain and the cerebrospinal fluid, embedded with white matter (WM) fiber tracts; second, a morphing approach for subject-specific head model generation via a new hierarchical image registration pipeline integrating Demons and Dramms deformable registration algorithms. The performance of the head model is evaluated by comparing model predictions with experimental data of brain–skull relative motion, brain strain, and intracranial pressure. To demonstrate the applicability of the head model and the pipeline, six subject-specific head models of largely varying intracranial volume and shape are generated, incorporated with subject-specific WM fiber tracts. DICE similarity coefficients for cranial, brain mask, local brain regions, and lateral ventricles are calculated to evaluate personalization accuracy, demonstrating the efficiency of the pipeline in generating detailed subject-specific head models achieving satisfactory element quality without further mesh repairing. The six head models are then subjected to the same concussive loading to study the sensitivity of brain strain to inter-subject variability of the brain and WM fiber morphology. The simulation results show significant differences in maximum principal strain and axonal strain in local brain regions (one-way ANOVA test, p < 0.001), as well as their locations also vary among the subjects, demonstrating the need to further investigate the significance of subject-specific models. The techniques developed in this study may contribute to better evaluation of individual brain injury and the development of individualized head protection systems in the future. This study also contains general aspects the research community may find useful: on the use of experimental brain strain close to or at injury level for head model validation; the hierarchical image registration pipeline can be used to morph other head models, such as smoothed-voxel models.

Head model personalization: A framework for morphing lifespan brain images and brains with substantial anatomical changes

“…The baseline FE head model (the ADAPT model) [35] has been generated based on the ICBM template image and has the same geometry as the ICBM image. The ADAPT Fmodel includes the brain, skull, meninges, CSF, and superior sagittal sinus (SSS) (Fig.…”

“…However, a known concern is a less accurate peak strain/stress predicted, especially at the surfaces due to jaggedness, thus is not preferred. Most state-of-the-art head injury models use conforming hexahedral elements despite the meshing challenges [35]. Besides the less developed meshing algorithms for hexahedrons, a necessity to include falx and tentorium due to the important structural influence on brain mechanical responses under an impact [36] poses an additional challenge for subject-specific head injury model generation; while these structures are often neglected in head models for tDCS, TMS and TUS.…”

“…Besides the less developed meshing algorithms for hexahedrons, a necessity to include falx and tentorium due to the important structural influence on brain mechanical responses under an impact [36] poses an additional challenge for subject-specific head injury model generation; while these structures are often neglected in head models for tDCS, TMS and TUS. A detailed analysis of the current meshing challenge for head injury models is found in a previous study [35].…”

“…FE head models without anatomical details such as sulci and gyri also hinder studying detailed mechanisms at areas of interest, such as CTEs with pathologies observed at sulcal depth [37]. Studies have also shown the brain sizes/shape influences brain response significantly under impact [35,38], suggesting the necessity to use personalized models to study the onset of TBI in real life. Along with the tremendous efforts being put on adult healthy FE head model generation, efforts on elderly, children, and infant models are less, being only a handful of models exists (e.g., [39][40][41][42][43][44][45][46]).…”

“…In particular, deformable image registration-based mesh morphing has been shown promising to personalize healthy brain models due to its capacity to capture the anatomical difference between the baseline and the subject image [35,61]. However, despite intensive efforts for decades, deformable image registration for subjects with substantial anatomical changes is still challenging and with limited registration performance [62].…”