Comparison of multi-excitation and multi-frequency MR elastography to estimate anisotropic mechanical properties of the human brain.

Motivation: MR elastography can estimate anisotropic mechanical properties of fibrous white matter, traditionally using multi-excitation approaches. Multi-frequency elastography from a single driver is more common and could expand measurements of anisotropy. Goal(s): Our goal was to compare mechanical anisotropy from multi-frequency and multi-excitation reconstructions. Approach: Transversely isotropic parameters were reconstructed using simulated and in vivo multi-frequency wave data, then compared between approaches and against ground truth maps. Adolescent and adult measurements were compared in white matter regions. Results: Multi-frequency elastography performed comparably with the multi-excitation approach in simulations. Higher shear anisotropy was observed in adults compared to adolescents, with no differences in tensile anisotropy. Impact: This study demonstrates that multi-frequency magnetic resonance elastography can reliably estimate anisotropic mechanical properties from single driver data, enabling broader application. Quantifying developmental changes in anisotropy of white matter provides new insights into brain mechanics during maturation.