Initial experimental results using ensemble tracking for 2D vector velocity measurement

The authors have previously described a time-domain speckle tracking method, called Ensemble Tracking, for two dimensional vector velocity measurement. Ensemble Tracking involves parallel receive processing, 2D pattern matching, and interpolation of the resulting tracking grid to estimate sub-pixel speckle translations between successive ultrasonic acquisitions. The result is a two dimensional vector velocity map of motion with high spatial and temporal resolution. Here, the authors describe a novel and computationally efficient interpolation algorithm, called Grid Slopes, which utilizes gradients of the pixel-based tracking grid. This algorithm provides accuracy comparable to more complex interpolation methods, as well as suitability for real-time implementation. In addition, the authors present results obtained with a string phantom and an experimental system that employs 4:1 parallel receive processing. These results indicate the ability to accurately measure sub-pixel translations of subresolution-sized kernels at a 90 degree transducer angle.