Objective: MR elastography (MRE) derives tissue shear stiffness from the wavelength of propagating shear waves. Geometric distortion can therefore alter the apparent wavelength and introduce errors in the calculated shear stiffness. This study evaluated how geometric distortion affects shear stiffness measurements in EPI-based MRE, with a focus on the phase-encoding orientation relative to the wave propagation direction and on the influence of vibration frequency. Materials and Methods: Phantom experiments were conducted with systematically varied phase-encoding directions and vibration frequencies to characterize distortion effects under controlled conditions. To assess distortion effects in a clinical setting, liver MRE was performed in three healthy volunteers. Distortion correction was applied in both experiments, and distortion effects were quantitatively evaluated by comparing shear stiffness values before and after correction. Results: The phantom experiments identified two factors that compromise measurement uniformity. First, the spatial uniformity of shear stiffness measurements decreased when the wave propagation direction was parallel to the phase-encoding direction (i.e., the direction along which distortion occurs). Second, this non-uniformity further increased as the propagating wavelength became shorter, which occurs at higher vibration frequencies or in softer tissue regions. In contrast, liver MRE in healthy volunteers showed minimal distortion effects (mean difference: 0.10 ± 0.15 kPa; 95% CI: ?0.28 to 0.48 kPa), suggesting that current clinical liver MRE protocols are largely unaffected by geometric distortion. Conclusion: As MRE is increasingly applied to organs beyond the liver, geometric distortion may become a more relevant source of error in these emerging applications. Careful consideration of wave propagation patterns and distortion characteristics is therefore essential for accurate and reliable MRE measurements across various organs.
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