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

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