Displacement field normalization in MR-elastography: phantom validation and in vivo application

MR-elastography aims at characterizing the mechanical properties of living tissues by probing wave propagation therein. Displacement fields are recorded over a mechanical cycle by encoding the inferred motion along the three spatial directions. Thus the complex shear viscoelastic moduli can be computed after inversion of the wave equation. Patients' motion during the MR-acquisition usually results in unrestrained spatial transformations of the targeted organ. It may also yield unwanted mismatch of the components of the acquired displacement fields. Spatial normalization of the phase image along the magnitude image tackles the correcting linear or non-linear transformations but, as numerically showed recently, displacement field normalization is required to fully recover the phase information in MR-elastography and improve the parametric reconstruction. Here, we experimentally validate the approach by applying these corrections on a breast phantom after MR-elastography exams for arbitrary three-dimensional rotations. This double normalization scheme was advantageously applied on a brain MR-elastography data set where the subject had involuntary moved during the acquisition.

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