Simultaneous imaging of tissue motion and flow velocity using 2D phase-coupled speckle tracking

We introduce a new method for simultaneous imag ing of tissue motion and flow with subsample accuracy in both axial and lateral directions. The method utilizes a phase-coupled 2D speckle tracking approach, which employs the true 2D complex cross correlation to find subpixel displacements in both axial and lateral directions. We have also modified the imaging sequence on a Sonix RP scanner to allow high frame rate 2D data collection in a limited field of view covering the region of interest (M2D-mode). Together with the robust 2D speckle tracking method, M2D imaging allows for capturing the full dynamics of the flow and wall/tissue motion, even when the flow is primarily in the lateral direction (with respect to the imaging beam). The fine vector displacement estimates in both axial and lateral directions are shown to allow for smooth and contiguous strain and shear strain calculations with minimal filtering. The quality of the displacement and strain fields is demonstrated by experimental results from a flow phantom (ATS Model 524) and in vivo images of the carotid artery in a healthy volunteer. The results clearly demonstrate the feasibility of simultaneous imaging of the vector flow field and the wall/tissue motion and the corresponding strains at high spatial and temporal sampling. This may provide an essential tool in modeling the fluid-solid interactions between the blood and blood vessel, a key challenge in vascular biomechanics.