Melanie Estrella | Searcharxiv

arXiv2025

In Vivo Wideband MR Elastography for Assessing Age-Related Viscoelastic Changes of the Human Brain

Magnetic Resonance Elastography (MRE) noninvasively maps 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 the 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; older: 50-63 years). Shear wave speed (SWS) maps were generated as a proxy for stiffness, and SWS dispersion was modeled using Newtonian, Kelvin-Voigt, and power-law rheological models. Whole-brain stiffness declined with age, with the strongest effect observed at low 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). Compared to older brains, younger adults showed 14.3% higher baseline stiffness in the power-law model (p=0.001) and 8.5-9.0% higher viscosity according to the Newtonian and Kelvin-Voigt model (p<0.05). White and cortical gray matter exhibited similar age-related decreases, while deep gray matter showed an increase in the power-law exponent (+0.001/year; p=0.036), suggesting a transition toward more fluid-like properties associated with aging. Wideband MRE revealed frequency-dependent and region-specific biomechanical alterations with aging, with the strongest effects observed at low frequencies. Extending brain MRE into the low frequency regime potentially enhances sensitivity to solid-fluid interactions. Therefore, low frequency MRE may serve as an early biomechanical marker of microstructural brain changes due to aging and neurodegeneration.

physics.med-ph↗

arXiv2025

Technical recommendation on multiplex MR elastography for tomographic mapping of abdominal stiffness with a focus on the pancreas and pancreatic ductal adenocarcinoma

Objectives: MR elastography (MRE) offers valuable mechanical tissue characterization, however, in deep abdominal organs like the pancreas conventional single-driver, single-frequency approaches often fail. This study evaluates whether multiplex MRE using multiple drivers and vibration frequencies can overcome these limitations. Methods: This study used single-shot spin-echo MRE in 18 healthy volunteers targeting the liver, pancreas, kidneys, and spleen. Each healthy volunteer underwent 16 MRE examinations with different sets of four vibration frequencies (30-60 Hz) and four driver combinations, and an additional null experiment without vibrations. Further, a cohort of 14 patients with pancreatic ductal adenocarcinoma (PDAC) were retrospectively assessed. The quality of shear-wave fields and stiffness maps was assessed by displacement amplitudes and image sharpness. Results: In healthy volunteers, abdominal coverage with displacement amplitudes above the pre-determined noise level of 4 {\mu}m varied between MRE configurations: 24.2% ([0.0%-56.2%], single-driver, 60 Hz), 66.9% ([24.8%-97.7%], single-driver, 30-60 Hz), 70.2% ([0.0%-92.5%], multi-driver, 60 Hz) and 99.9% ([89.4%-100%], multi-driver, 30-60 Hz). In the pancreas, >60% coverage was achieved in all subjects using four drivers and multiple frequencies. This was achieved in only 2/18 subjects using single-driver/single-frequency MRE. Patients with PDAC had 99.1% [91.4%-100%] coverage in the pancreas and 96.3% [63.1%-100%] abdominal coverage (multi-driver, 30-60 Hz). Conclusion: MRE with four drivers and multiple vibration frequencies between 30-60 Hz enables tomographic mapping of tissue stiffness across the entire abdomen, including the pancreas. Multiplex MRE offers a promising approach for generating detailed images of abdominal stiffness, potentially enhancing clinical diagnostics for abdominal and pancreatic diseases.

physics.med-ph↗