MR elastography-based detection of impaired skull-brain mechanical decoupling performance in response to repetitive head impacts

Objective: To evaluate MR elastography (MRE)-assessed biomarkers for detecting changes in skull-brain mechanical decoupling performance induced by repetitive head impacts (RHIs).

Methods: This prospective single-center study enrolled 80 asymptomatic participants (2017-2023) divided into three groups: no exposure (RHI(-)), low-impact (low RHI(+)), and high-impact (high RHI(+)). Four MRE-based parameters were evaluated to analyze the skull-brain decoupling performance: brain-to-skull rotational transmission ratio (Rtr), cortical shear strain (normalized OSS (octahedral shear strain)), cortical volumetric strain (normalized ONS (octahedral normal strain)), and the OSS-to-ONS ratio. Confounding factors (age/skull-brain distance, sex) were controlled with a linear regression model. One-way ANOVA with Tukey's post-hoc test was used for group comparisons.

Results: The high RHI(+) showed a significantly increased adjusted Rtr compared to the RHI(-) and low RHI(+) (p < 0.001). Higher adjusted OSS-to-ONS ratios were found in the high RHI(+) in the frontal (q < 0.05), parietal (q < 0.001), and occipital (q < 0.05) lobes compared to the RHI(-), and in all regions compared to the low RHI(+) (q < 0.05). The high RHI(+) exhibited lower adjusted normalized ONS and OSS in the temporal lobe (q < 0.05) compared to the low RHI(+). These findings suggest that recent and prolonged RHI exposures may impair the skull-brain decoupling performance, affecting the capacity of the interface to isolate the brain by dampening skull-to-brain motion transmission and modulating brain surface deformation.

Conclusion: This study reveals evidence of impaired decoupling function at the skull-brain interface resulting from RHI exposure and demonstrates MRE-based biomarkers for early detection of this impairment.

Key points: Question The skull-brain interface is crucial for brain protection under impact, but its early mechanical responses to repetitive head impacts (RHIs) remain largely unknown. Findings Mechanical changes (more rotation and a shift in shear relative to volumetric strain) across the skull-brain interface were observed in participants under high RHI exposure. Clinical relevance Our study developed MR elastography (MRE)-based measurements to detect changes in the skull-brain interface caused by RHI, suggesting that MRE holds promise for noninvasively quantifying cumulative injury and potential future clinical interventions for individuals with high RHI exposure.