A new method for two-dimensional myocardial strain estimation by ultrasound: an in-vivo comparison with sonomicrometry

At present, ultrasonic strain and strain rate imaging only give information (in the deformation occurring along the image line. As a result. the techniques have been shown to be angle dependent. As a first step to overcome this problem. fully resolved two-dimensional (2D) strain estimates are required. Hereto, a new methodology for the estimation of 2D strain has been developed in our lab based on in-silico and in-vitro experiments. The aim if this study was to further develop and validate this new methodology in an in-vivo setting. In 5 open chest sheep, ultrasound RF data were acquired in a parasternal long axis view using a Toshiba PowerVision 6000 equipped with an RF interface. Myocardial radial and longitudinal strain components were simultaneously estimated in the inferolateral wall using the new methodology from single RF data sets. Four segment-length sonomicrometry crystals were placed in a tetrahedral configuration just lateral to the imaging plane giving a continuous reference for the longitudinal and radial strain components. After baseline acquisitions. the deformation was altered by pharmacologically changing the inotropic state of the myocardium and by inducing ischemia by occlusion of a distal branch of the circumflex coronary artery. Ultrasonically estimated peak systolic radial and longitudinal strain were validated against sonomicrometry by means of linear regression and Bland-Altinan analysis. For both strain components good agreements were found between the ultrasound and the sonomicrometry measurements as shown by Bland-Altman. For the radial strain estimates, the correlation coefficient was found to he r = 0.94 with epsilon(us) = 1.20 epsilon(sm), + 0.5, while for the longitudinal component, the correlation coefficient was r = 0.95 with epsilon(us) = 1.07 epsilon(sm), + 1. Conclusion: Simultaneous estimation of both in-plane myocardial strain components using our new methodology showed to give accurate information on myocardial deformation in the in-vivo setting. Myocardial strain can thus be assessed in-plane. independent of insonation angle. This could potentially accelerate the clinical acceptance of deformation imaging in cardiology.