Ultrasound echo decorrelation due to acoustic radiation force

Several groups have proposed the use of acoustic radiation force as a means to characterize the mechanical properties of biological tissues. These approaches are based on the estimation of time delays between successively acquired echo lines when an internal deformation is applied. The ensemble of these delays forms a time-displacement curve that holds information about the viscoelastic response of the tissue under interrogation. The performance of such techniques is strongly dependent on the accuracy of the time delay estimates. Although noise places significant limits on the estimation process, echo decorrelation will also contribute to reduce the quality of the delay estimates. This decorrelation is similar to that observed in conventional axial elastography, even though the deformation field that results from acoustic radiation force is more complex than the one produced by axial elastography. In this paper we use analytical and computational methods to predict the decorrelation generated in acoustic radiation force imaging. We substitute derived correlation coefficients into the Cramer-Rao Lower Bound (CRLB) to predict fundamental limits on the performance of radiation force based elasticity estimation.