Fig. 1.
A depiction of the relationship between differential scatterer motion and uncertainty in displacement estimation. A spatially varying acoustic radiation force field is applied to a set of targets over N acquisitions from time t0 to tN−1. The nonuniform force field induces a gradient of scatterer displacements across the point spread function (PSF). In the illustration, different displacements are associated with different shades of gray circles (scatterers) in the target field. The echo signals from all scatterers across the PSF are summed to give the resulting received echo. The delays in echo signals from different sets of scatterers are illustrated prior to the summation node at the transducer. As the gradient of displacements increases through acquisition time, the correlation between successive received echoes decreases, which results in increasing uncertainty in displacement estimates. The displacement profile estimated from the received echo signal is illustrated as the solid line with error bars, indicating uncertainty in the displacement estimate. The dashed lines correspond to the different sets of scatterers and indicate the actual displacements of these scatterers.