Single track location viscosity estimation by maximum likelihood estimation

Single Track Location (STL) Acoustic Radiation Force Impulse (ARFI) imaging has been demonstrated in the setting of linear elastic materials. However, biological tissues are viscoelastic causing shearwave dispersion. As a result, the use of cross-correlation to estimate shearwave speed is not optimal. Specifically, the assumption of shift-invariance is violated. Single Track Location Viscosity Estimation (STL-VE) is an alternative reconstruction that overcomes this limitation by applying a viscoelastic model to the reconstruction. Constraints on the problem such as a limited range and number of tracking locations, and a limited number of time samples make naive frequency domain reconstructions challenging. Instead, we introduce an time domain reconstruction based on the maximum likelihood estimator (MLE). Improved accuracy compared to fitting directly to the signal phase data is demonstrated. The effect of geometry assumptions on the estimation results are explored. Error introduced by spectrum based estimation is demonstrated for trunctated data. Finally, the importance of using a single tracking location is demonstrated.