Axonal tract-integrated finite element brain model for predicting mild traumatic brain injury based on axonal strain

Mild traumatic brain injury (mTBI), or concussion, is a prevalent public health issue that imposes a substantial economic and social burden on individuals and healthcare systems. Although mTBI is often attributed to brain deformation induced by angular acceleration of the head, its precise mechanisms, including the relationship between local deformations of the brain parenchyma or axonal fibers and clinical symptoms, have not yet been elucidated. Finite element (FE) models of the human brain have been widely used to estimate brain strain in various impact scenarios associated with mTBI. However, despite the possibility that mTBI-related neuropathological changes may involve disruptions of neural pathways connecting different brain regions, most existing models do not account for the architecture of axonal fibers at the anatomical tract level. This study proposes an advanced human brain FE model that explicitly incorporates axonal fiber tracts derived from a group-averaged tractography atlas. The tracts were embedded as a series of continuous beam elements into the solid elements of the brain parenchyma, enabling dynamic evaluation of axonal strain for each tract during head impacts. The model was validated against experimental data on brain deformation from postmortem human subject tests and exhibited comparable or superior correlation scores relative to existing models. Reconstruction simulations of eight real-world mTBI cases, including both vehicular- and sports-related impacts, were conducted using the developed model by comparing two axonal strain-based injury metrics across the cases. The results consistently showed higher injury metrics in specific tract, including the posterior thalamic radiation, body of the corpus callosum, frontal aslant tract, posterior corticostriatal tract, medial lemniscus, parietal corticopontine tract, and superior longitudinal fasciculus. Additionally, horizontal head rotation contributed more significantly to tract-level injury metrics than coronal or sagittal rotation. These findings provide new biomechanical insight into the relationship between mTBI and tract-level axonal damage. Furthermore, the proposed brain FE model may serve as a foundation for understanding mTBI mechanisms from a structural and functional connectome perspective, as a step toward improved mTBI prediction.