Influence of system geometry on motion tracking in echocardiographic image sequences

In this paper, we present a study on motion tracking in echocardiographic ultrasound images. The difficulty of motion estimation is linked to the fact that echographic image formation induces decorrelation between the underlying motion of tissue and the observed speckle motion. We investigate in this work the influence of speckle decorrelation on motion estimation from realistic simulations using Field II. In particular, the analysis is performed for two simple motions: a translation and an incompressible deformation. The influence of decorrelation on speckle tracking accuracy is quantified using a conventional block matching (BM) algorithm and a more recent algorithm based on bilinear deformable block matching (BDBM). For all the simulations, the influence of the sectorial acquisition geometry is also investigated by performing motion estimation on Cartesian and polar data. Results show that decorrelation and loss of accuracy are significantly larger when motion estimation is performed from the conventional interpolated Cartesian data. In this perspective, we also show that the accuracy of motion estimation can be improved by using the BDBM algorithm, which may to some extent compensate for the deformation of the speckle patterns induced by decorrelation and sectorial geometry.