ENSEMBLE TRACKING FOR 2D VECTOR VELOCITY-MEASUREMENT - EXPERIMENTAL AND INITIAL CLINICAL-RESULTS

We describe a new method, called Ensemble Tracking, for estimating two -dimensional velocities with ultrasound. Compared to previous speckle tracking techniques, Ensemble Tracking measures motion over smaller ti mes and distances, increasing maximum velocities and reducing errors d ue to echo decorrelation. Ensemble Tracking uses parallel receive proc essing, 2D pattern matching, and interpolation of the resulting tracki ng grid to estimate subpixel speckle translations between successive u ltrasonic acquisitions. In this study, small translations of a tissue mimicking phantom were quantified at transducer angles of 0 degrees, 4 5 degrees, and 90 degrees. Measurements over three parallel beam spaci ngs and all transducer angles had mean errors from -4% to +11%, when p arallel beam amplitudes were normalized. Such amplitude normalization substantially improved results at 45 degrees and 90 degrees. The ampli tude, spacing, and correlation between the parallel beams were quantif ied, and their effects on the accuracy and precision of estimates are discussed. Finally, initial clinical results demonstrate the ability t o track and display blood flow in the carotid artery.