Angle-independent strain mapping in myocardial elastography - 2D strain tensor characterization and principal component imaging

A current limitation of the implementation of myocardial elastography in a clinical setting is the difficulty of interpreting the one-dimensional strain maps due to varying strain values in the wall of the left ventricle (LV). In this paper, we demonstrate a robust angle-independent method for 2D myocardial elastography on simulated 2D ultrasonic images of a 3D finite-element analysis (FEA) model of the LV. Two FEA, a control and a regionally ischemic, canine left-ventricular models, were used and model states were obtained in increments and accumulated from end-diastole (ED) to end-systole (ES). Two-dimensional (21)) displacement in the myocardium. was estimated between ED to ES. These estimates were good approximations of the FEA solution (rms errors of 0.18 min for lateral displacement and 0.12 min for axial displacement). The 2D symmetric strain tensor was calculated from the displacements and angle-independent principal strains were obtained using eigenvalue decomposition of the strain tensor. Principal strains in the myocardium have been shown to approximate normal strains with respect to an anatomical coordinate system [5]. To test this angle-independence, displacements were obtained from two different orthogonally placed transducer locations. Principal strains were estimated from both locations and showed good correlation to the FEA solution. Rms errors between the FEA model and 2D elastography (2DE) estimation of principal strains from both transducer locations were 1.7% and 2.4% strain, respectively. Visualizing the transmural strain using principal strains greatly simplified their interpretation. Moreover, abnormal deformation of the ischemic region, which was difficult to observe with axial and lateral strains, was clearly visible in the principal strain images. In summary, the feasibility of 2D elastography estimation of myocardial displacement and strain was shown. In this paper, we propose the use of principal strains as a more useful tool in the visualization of abnormal wall motion and the detection of ischemia and other related heart diseases.