Multimodal characterization of intracranial biomechanics in a 3D biofidelic head surrogate

Rapid head motion causes the brain to deform, which may lead to acute and chronic consequences to normal brain health and function. Since the risk and severity of brain injury correlates with brain strain, computational and physical models of the brain response to impact are commonly used to assess risk and evaluate safety devices in silico. Most physical head surrogates that are used for equipment evaluation, however, are simplified and lack internal measures of brain deformation, relying instead on the interpretation of the resulting head kinematics to predict injury. Developing a more biofidelic physical brain surrogate to improve brain injury risk assessments requires the use of experimental brain motion data. Two techniques, sonomicrometry and tagged magnetic resonance imaging (tMRI), have been independently developed to characterize the in situ and in vivo brain response. Combining data acquired from both techniques can leverage the advantages of each method while alleviating the limitations. The objectives of this study were to create a head surrogate with realistic intracranial geometry and brain simulant for use in multimodal brain deformation experiments. Six gel simulants were tested using shear rheometry, with Sylgard 527 chosen as the best simulant for this study. The headform was created using the average geometry from an MRI template of 20 healthy volunteers, and was tested under non-injurious loading conditions using tMRI and sonomicrometry. The prototype headform showed good contrast in T1-weighted MRI and captured similar strain patterns when compared to the in vivo human response, although maximum principal strains (MPS) were approximately double what is measured in vivo. The two techniques showed good correspondence in brain motion response with trade-offs in temporal resolution and measurement density. Both techniques also showed similar displacement and strain magnitudes with a finite element simulation of the headform. Future studies will focus on including a more realistic sliding condition between skull and brain, as well as optimizing the material properties to better match the in vivo and in situ data.