Evaluation of Wave Delivery Methodology for Brain MRE: Insights from Computational Simulations

Purpose: Magnetic resonance elastography (MRE) of the brain is being explored as a biomarker of neurodegenerative disease such as dementia. However, MRE measures for healthy brain have varied widely. Differing wave delivery methodologies may have influenced this, hence finite element-based simulations were carried out to explore this possibility. Methods: The natural frequencies of a series of cranial models were calculated, and MRE-associated vibration was simulated for different wave delivery methods at varying frequency. Displacement fields and the corresponding brain constitutive properties estimated by standard inversion techniques were compared across delivery methods and frequencies. Results: The delivery methods produced widely different MRE displacement fields and inversions. Furthermore, resonances at natural frequencies influenced the displacement patterns. Two of the wave delivery methods (head-cradle and acoustic pillow) gave rise to lower inversion errors, e.g., at 90 Hz the error in the storage modulus was 11% less than for the bite-bar method. Conclusion: Wave delivery has an important impact on brain MRE reliability. Assuming small variations in brain biomechanics, as recently reported to accompany neurodegenerative disease (e.g., 7% for Alzheimer's disease), the effect of wave delivery is important. Hence, a consensus should be established on the optimum methodology, to ensure diagnostic and prognostic consistency.