Tissue-Level Stresses Within the Brain During Rotationally-Induced mTBI:
A Three-Dimensional Finite Element Model of the Rat Coupled with Experiments

To quantify anatomical region-dependent tissue-level stresses during head rotational acceleration sufficient to induce mTBI. METHODS: A unique hybrid experimental-computational approach was employed. The experimental study subjected thirty-one adult Sprague Dawley rats to mTBI using the MCW Rotational Injury Device. Rats were divided into five experimental groups with different rotational acceleration pulses that independently increased rotational acceleration magnitude to three levels while holding duration constant and increased duration to three levels while holding magnitude constant. Following injury, unconscious time was measured from administration of anesthesia reversal agent to return of the corneal reflex and histological evidence of injury was measured using GFAP. The FEM was developed using high-resolution CT and MR images of rats. The mesh consisted of six anatomical structures, with cerebrum subdivided into 18 anatomical regions. Anatomical region-based peak stresses and an integrated stress-time metric from the FEM were compared to experimental unconscious times and histological evidence of injury. RESULTS: Greater experimental unconscious times (i.e., injury severities) were associated with increases in rotational acceleration magnitude and duration. Maximum FEM Von Mises stresses, maximum FEM stress-time magnitudes, and greatest histological evidence of injury were obtained in the hippocampus. Peak stresses increased with increasing acceleration magnitude, which agreed with unconscious times and histological evidence of injury. However, while unconscious times and evidence of injury increased for increasing durations, maximum FEM stresses did not. Conversely, the stress-time metric matched increases in unconscious time and evidence of injury for increasing acceleration magnitude and duration. CONCLUSIONS: Results of this unique hybrid analysis indicate that the integrated stress-time variable may be more suited to explain variation of mTBI severity than pure peak metrics (e.g., Von Mises stress). These findings highlight the independent roles that head rotational acceleration magnitude and duration play in modulating injury type and severity, and region-specific biomechanical correlates for mTBI.

The Author

Dr. Daniel Baumgartner
Associate Professor
University of Strasbourg
imfs
2 rue boussingault
67000 Strasbourg, France

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