Measurement of local wavelength using MR elastography with multiple phase offsets

Magnetic resonance elastography (MRE) is a phase-contrast-based MR method that can visualize propagating strain waves in materials. Quantitative values of shear modulus can be calculated by estimating the local wavelength (LW) of the wave pattern. Low frequency mechanical motion must be used for soft tissue-like materials, because strain waves rapidly attenuate at higher frequencies. Therefore, it is difficult to estimate LW with high spatial resolution especially from noisy MRE images. In the MRE sequence a motion-sensitizing gradient (MSG) is synchronized with the mechanical cyclic motion. MRE images with multiple phase offsets can be generated with increasing delays between MSG and the mechanical excitation. In this report, the authors describe a new algorithm in order to measure LW at higher spatial resolution using MRE images with multiple phase offsets. This method was evaluated by computer simulation and a phantom study. The results show that LW was successively estimated.