Deformable models for tagged MR images: reconstruction of two- and three-dimensional heart wall motion

Magnetic resonance (MR) tissue tagging allows non-invasive in vivo measurement of soft tissue deformation. Planes of magnetic saturation are created, orthogonal to the imaging plane, which form dark lines (stripes) on the image. These stripes deform with the tissue and may be tracked in order to reconstruct the time-varying deformation of the structure. The authors have developed a semiautomatic line tracking algorithm to track the stripes to sub-pixel resolution throughout the deformation, based on active contour models (snakes). Each tracked stripe point gives displacement information orthogonal to the original tagging plane, i.e. a one dimensional constraint on the motion. Data from several tagging and imaging planes in different orientations was combined using a deformable model of the LV wall. Two or three dimensional motion and deformation was then reconstructed by fitting the data constraints by linear least squares