Fig 3.

Modulus estimates (first column) and the error in the shear viscosity estimates (second column) are presented for simulated data using the Kelvin-Voigt Maximum Liklihood Estimation (KV-MLE) assuming either cylindrical or plane wave models. The simulation modulus is fixed at 2 kPa while the simulation viscosity is varied from 0.5 to 1.0 Pa·s. Each row contains a different simulation geometry. In the first row, a cylindrical wave geometry is produced by using an Gaussian excitation with a FWHM of 1 mm in both the elevational and lateral directions. In the second row, a plane wave is approximated by setting the FWHM in the elevational direction to 10 cm while the FWHM in the lateral direction is kept at 1 mm. This only approximates plane waves since the grid size is not infinite. In the third row, an intermediate geometry is simulated. For the cylindrical simulation, there is good agreement between the simulated modulus/viscosity and the reconstructed values when a cylindrical wave geometry is assumed. Similarly for the plane simulation, there is good (although not perfect) agreement between the simulated modulus/viscosity and the reconstructed values when a plane wave geometry is assumed. Both assumptions fail for the intermediate geometry. Importantly, the intermediate geometry does not produce an intermediate error in the measurements. Instead, the measurements are markedly biased even at low viscosity.