Acoustic Detection of Intracranial Cavitation Induced by Blunt Impacts in Polyacrylamide Human Head Models Across Varying Orientations.

Abstract

Traumatic brain injury remains a major health concern among civilians and military personnel, with intracranial cavitation hypothesized as a damage mechanism during blunt impacts. This study examines cavitation bubble activity in simplified polyacrylamide human head models, focusing on different anatomical regions and imaging modalities. A drop tower setup with high-speed acoustic and optical imaging was used to characterize the onset, expansion, and collapse of bubbles and assess the impact orientation's effects. Acoustic plane wave imaging and passive cavitation detection captured emissions linked to bubble dynamics. Although plane wave imaging was affected by reflections, it detected bubble growth effectively. In contrast, passive cavitation detection showed greater sensitivity during collapse, with broadband spectral responses. Signal processing extracted relevant spectral features from both modalities, regardless of pre-existing bubble nuclei. Cavitation behavior varied across models, with impact angle influencing both timing and persistence, suggesting orientation affects injury mechanisms. When the head model was impacted at a 90° angle and observed along the central sulcus, cavitation onset occurred earliest with the strongest shockwave reflections, likely due to changes in wave travel distance between the coup and contrecoup sites. Head models with artificial dampeners showed that the scalp and dura mater layers reduced cavitation intensity, though cavitation remained detectable. This work supports the feasibility of acoustically detecting impact-induced cavitation as a standalone tool, informing strategies for transcranial monitoring and protective gear design in blunt trauma scenarios.