📝 SummarXiv

Abstract

Magnetic Resonance Elastography (MRE) provides maps of brain biomechanics and is highly sensitive to alterations associated with aging and neurodegenerative disease. Most implementations use a single frequency or a narrow frequency band, limiting analysis of frequency-dependent viscoelastic parameters. We developed a dual-actuator wideband MRE (5-50 Hz) protocol and acquired wavefields at 13 frequencies in 24 healthy adults (young: 23-39 years; old: 50-63 years). Shear wave speed (SWS) maps were generated as a proxy for stiffness, and SWS dispersion was modeled with Newtonian, Kelvin-Voigt, and power-law models. Full brain SWS declines with age, most strongly at lower frequencies (5-16 Hz: -0.24%/year; p=0.019) compared with mid (20-35 Hz: -0.12%/year; p=0.030) and high frequencies (40-50 Hz: -0.10%/year; p=0.165). Power-law baseline SWS was higher in younger than in older adults (0.14$\pm$0.01 m/s vs 0.12$\pm$0.0035 m/s; p=0.018), and viscosity was also higher (Newtonian model: 7.43$\pm$0.35 vs 6.85$\pm$0.37 Pa$\cdot$s; p=0.003; Kelvin-Voigt: 7.99$\pm$0.36 vs. 7.40$\pm$0.45 Pa$\cdot$s; p=0.007). Regionally, white matter and cortical gray matter showed similar age-related declines in power-law SWS and viscosity. In deep gray matter the power-law exponent unusually increased with age (0.0010/year; p=0.036), indicating a transition toward softer, fluid-like tissue properties in that region. Wideband MRE with viscoelastic modeling resolved frequency-dependent and regional aging signatures. Sensitivity was greatest at low frequencies, highlighting this range as promising for detecting microstructural alterations in aging and neurodegeneration.