title: Lagrangian speckle model and tissue-motion estimation--theory.
abstract: It is known that when a tissue is subjected to movements such as rotation, shearing, scaling, etc., changes in speckle patterns that result act as a noise source, often responsible for most of the displacement-estimate variance. From a modeling point of view, these changes can be thought of as resulting from two mechanisms: one is the motion of the speckles and the other, the alterations of their morphology. In this paper, we propose a new tissue-motion estimator to counteract these speckle decorrelation effects. The estimator is based on a Lagrangian description of the speckle motion. This description allows us to follow local characteristics of the speckle field as if they were a material property. This method leads to an analytical description of the decorrelation in a way which enables the derivation of an appropriate inverse filter for speckle restoration. The filter is appropriate for linear geometrical transformation of the scattering function (LT), i.e., a constant-strain region of interest (ROI). As the LT itself is a parameter of the filter, a tissue-motion estimator can be formulated as a nonlinear minimization problem, seeking the best match between the pre-tissue-motion image and a restored-speckle post-motion image. The method is tested, using simulated radio-frequency (RF) images of tissue undergoing axial shear.
authors.affiliation: Institut de Cardiologie de Montréal, Canada.
authors.forename: R L
authors.initials: RL
authors.lastname: Maurice
authors.forename: M
authors.initials: M
authors.lastname: Bertrand
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008962:Models, Theoretical; D009132:Muscles / Q000000981:diagnostic imaging* / Q000502:physiology; D014463:Ultrasonography