Lateral speckle tracking using synthetic lateral phase.

In traditional speckle tracking, lateral displacement (perpendicular to the beam direction) estimates are much less accurate than axial ones (along the beam direction). The accuracy of lateral tracking is very important whenever spatial derivatives of both axial and lateral displacements are required to give a full description of a two-dimensional (2-D) strain field. A number of methods have been proposed to improve lateral tracking by increasing the sampling rate in the lateral direction. We propose an alternate method using synthetic lateral phase (SLP). The algorithm, a direct analog of the phase zero-crossing approach used in axial displacement estimation, synthesizes the lateral phase first, then performs a zero-crossing detection on this synthetic phase to obtain lateral displacement estimates. The SLP is available by simply eliminating either the positive or negative half of the lateral spectrum of the original analytic signal. No new data need to be acquired for this procedure. This new algorithm was tested on both simulations and measurements from a cardiac phantom model. Results show that the method greatly improves the accuracy of lateral tracking, especially for low strain cases (< or =1%). The standard deviation of the estimation error of the lateral normal strain obtained with this approach has an approximate factor of 2-3 improvement for low strain cases. The conceptual and computational simplicity of this new method makes it a practical approach to improve lateral tracking for elasticity imaging.