3D Elasticity imaging using principal stretches on an open-chest dog heart

Ultrasound strain imaging has demonstrated its ability to quantitatively assess myocardial viability and contractility altered by myocardial ischemia. However, current ultrasound strain imaging methods still use lower dimensional methods to monitor 3D heart motion. Some 3-D tracking algorithms have also been developed recently in different groups. Quantitative analysis using current methods depends on ultrasound probe orientation and selection of a centroid. To address this, 3D elasticity imaging derived using principal stretches independent of the centroid point is used to assess the contractility of myocardial fibers with 3D data from a commercial 3D scanner on an open-chest dog heart. In this study, an open-chest dog was performed according to a Yale institutional animal protocol and 3D radio frequency (RF) volume data were acquired using an commercial 2D phased array (iE33, Philips, Andover, MA) placed in front of the anterior wall of the left-ventricle with a small water stand-off. 3D speckle tracking was applied to estimate 3D displacement with tracking resolution of 1.2 mm in the axial direction and 4.5 mm in azimuthal and zenithal directions. Volume-to-volume tracking results were accumulated referenced to the heart geometry at the end of diastole until the end of systole. Three principal stretches were estimated using eigenvalue decomposition of the derived right Cauchy deformation tensor at each point. Initial results of strains based on principal stretch and the principal direction has successfully demonstrated that heart wall is thickening along the radial direction and shortening along the longitudinal direction during systole. Unlike 1D or 2D methods, 3D speckle tracking can estimate myocardium's three-dimensional motion. Three strains based on the principal stretches were derived from 3D displacements to assess myocardial contractility independent of probe position and the selection of the centroid point.