Yücel Karabiyik will go through the paper "Waveguide effects and implications for cardiac magnetic resonance elastography: A finite element study" and there will be a discussion afterwards.
Abstract: Magnetic resonance elastography (MRE) is increasingly being applied to thin or small structures in which wave propagation is dominated by waveguide effects, which can
substantially bias stiffness results with common processing approaches. The purpose
of this work was to investigate the importance of such biases and artifacts on MRE
inversion results in: (i) various idealized 2D and 3D geometries with one or more
dimensions that are small relative to the shear wavelength; and (ii) a realistic cardiac
geometry. Finite element models were created using simple 2D geometries as well
as a simplified and a realistic 3D cardiac geometry, and simulated displacements
acquired by MRE from harmonic excitations from 60 to 220 Hz across a range of
frequencies. The displacement wave fields were inverted with direct inversion of
the Helmholtz equation with and without the application of bandpass filtering and/
or the curl operator to the displacement field. In all geometries considered, and at
all frequencies considered, strong biases and artifacts were present in inversion
results when the curl operator was not applied. Bandpass filtering without the curl
was not sufficient to yield accurate recovery. In the 3D geometries, strong biases
and artifacts were present in 2D inversions even when the curl was applied, while
only 3D inversions with application of the curl yielded accurate recovery of the
complex shear modulus. These results establish that taking the curl of the wave field
and performing a full 3D inversion are both necessary steps for accurate estimation of
the shear modulus both in simple thin‐walled or small structures and in a realistic
cardiac geometry when using simple inversions that neglect the hydrostatic pressure
term. In practice, sufficient wave amplitude, signal‐to‐noise ratio, and resolution will
be required to achieve accurate results.