Strain energy and kinetic energy in the human brain were estimated by magnetic resonance elastography during harmonic excitation of the head, and compared to characterize the effect of loading direction and frequency on brain deformation. In brain MRE, shear waves are induced by external vibration of the skull and imaged by a modified MR imaging sequence; the resulting harmonic displacement fields are typically"inverted" to estimate mechanical properties, like stiffness or damping.
Lateral loading induced primarily left-right head motion and rotation about the long axis of the neck; occipital loading induced anterior-posterior head motion and rotation in the sagittal plane. The ratio of strain energy to kinetic energy depended strongly on both direction and frequency. The ratio SE/KE was approximately four times larger for lateral excitation than for occipital excitation, and was largest at the lowest excitation frequencies studied.