Ensemble tracking: a new method for 2D vector velocity measurement

The authors describe a new method, called ensemble tracking, for quantifying two dimensional velocities. Compared to previous two-dimensional speckle tracking techniques, ensemble tracking measures motion over smaller translations, thereby reducing errors due to speckle decorrelation. The technique involves acquisition of an ensemble of 2D line sets along a single line of sight using parallel receive processing. This ensemble may be thought of as a sequence of 2D “snapshots” of the same spatial region at different time instants. A kernel region in each snapshot is tracked within slightly larger search regions in subsequent snapshots, providing velocity estimates at multiple time lags. Interpolation is employed to provide velocity estimates for sub-pixel translations that occur in the short time intervals between parallel acquisitions. The authors present the results of initial computer simulations indicating the ability to track such sub-pixel translations, and discuss directions for further research in this area