Publications by Author: Ahmed A. Alshareef

Objective: Computational models of the brain are typically validated using individual subjects from datasets of brain motion, but a comparison to an individual subject does not consider the biomechanical variation that naturally exists in the population. When data from multiple subjects is available, biomechanical corridors are constructed for the assessment of model biofidelity. However, a robust set of corridors for brain's biomechanical response due to applied head kinematics does not exist for model validation. The aim of this study was to create corridors based on a dataset of in situ brain displacement that included six specimens tested under a set of twelve loading conditions.

Methods: There were three main factors that complicated this task, including variation in head kinematics, differences in the initial position of the sensors, and the clustering of spatially scattered data. We employed various numerical and statistical methods to account for these experimental variations, with optimization and validation of the techniques conducted using the existing in situ dataset and a computational brain model.

Results: Corridors were constructed using average and standard deviation of the specimen responses in the dataset for 24 discrete locations within the brain. Peak displacement showed a variance of less than 30% for most brain sensor locations.

Conclusion: The corridors will serve as a better validation tool for assessing the biofidelity of computational brain models and will help understand inter-subject variability in brain biomechanics.

Traumatic brain injuries (TBIs) occur from rapid head motion that results in brain deformation. Computational models are typically used to estimate brain deformation to predict risk of injury and evaluate the effectiveness of safety countermeasures. The accuracy of these models relies on validation to experimental brain deformation data. In this study, we create the first group-average biomechanical responses of the brain, including structure, material properties, and deformation response, by age and sex from 157 subjects. Subjects were sorted intro three age groups—young, mid-age, and older—and by sex to create group-average neuroanatomy, material properties, and brain deformation response to non-injurious loading using structural and specialized magnetic resonance imaging data. Computational models were also built using the group-average geometry and material properties for each of the six groups. The material properties did not depend on sex, but showed a decrease in shear stiffness in the older adult group. The brain deformation response also showed differences in the distribution of strain and a decrease in the magnitude of maximum strain in the older adult group. The computational models were simulated using the same non-injurious loading conditions as the subject data. While the models’ strain response showed differences among the models, there were no clear relationships with age. Further studies, both modeling and experimental, with more data from subjects in each age group, are needed to clarify the mechanisms underlying the observed changes in strain response with age, and for computational models to better match the trends observed across the group-average responses.