In vivo characterization of 3D skull and brain motion during dynamic head vibration using magnetic resonance elastography

Abstract

Purpose: To introduce newly developed MR elastography (MRE)-based dual-saturation imaging and dual-sensitivity motion encoding schemes to directly measure in vivo skull–brain motion, and to study the skull–brain coupling in volunteers with these approaches. Methods: Six volunteers were scanned with a high-performance compact 3T-MRI scanner. The skull–brain MRE images were obtained with a dual-saturation imaging where the skull and brain motion were acquired with fat- and water-suppression scans, respectively. A dual-sensitivity motion encoding scheme was applied to estimate the heavily wrapped phase in skull by the simultaneous acquisition of both low- and high-sensitivity phase during a single MRE exam. The low-sensitivity phase was used to guide unwrapping of the high-sensitivity phase. The amplitude and temporal phase delay of the rigid-body motion between the skull and brain was measured, and the skull–brain interface was visualized by slip interface imaging (SII). Results: Both skull and brain motion can be successfully acquired and unwrapped. The skull–brain motion analysis demonstrated the motion transmission from the skull to the brain is attenuated in amplitude and delayed. However, this attenuation (%) and delay (rad) were considerably greater with rotation (59 ± 7%, 0.68 ± 0.14 rad) than with translation (92 ± 5%, 0.04 ± 0.02 rad). With SII the skull–brain slip interface was not completely evident, and the slip pattern was spatially heterogeneous. Conclusion: This study provides a framework for acquiring in vivo voxel-based skull and brain displacement using MRE that can be used to characterize the skull–brain coupling system for understanding of mechanical brain protection mechanisms, which has potential to facilitate risk management for future injury.