An Evaluation of Tentorium and Brainstem Influences on Intracranial Displacements and Strains

Headforms are commonly used as tools in the design and qualification of personal protective equipment. Deformable headforms, containing elastomeric brain models, provide a unique opportunity to directly measure the in situ intracranial strain from an impact; however, these physical models require significant refinement to ensure biofidelity. In the present work, the response and biofidelity of a deformable headform and brain model were investigated, comparing the influence of different boundary conditions on its response. More precisely, the presence or absence of a tentorium or a brainstem model were investigated, focusing on the resulting intracranial displacement and strain fields. The headforms were subjected to a series of linear impacts and deformations within the brain were tracked using embedded radiopaque markers and high-speed X-ray imaging. X-Ray Digital Image Correlation was used to calculate displacement and strain fields within the headform. The biofidelity of the displacement and strain fields within the headform design having both a tentorium and a brainstem were compared to Post-Mortem Human Subject (PMHS) data under identical impact conditions. The biofidelity was ranked using a CORA analysis to provide insight for future design refinements of the headform. The biofidelity ratings for displacement were highest in the frontal and occipital regions (good-excellent) and were worst in the insular region (marginal). Meanwhile, the strain biofidelity rating was best in the frontal (good) and cerebellum (good) regions and worst in the insular region (poor-marginal). This work addresses previous limitations in enhancing the biofidelity of closed headforms and offers opportunities for further improvement through the comparison to PMHS data.