Elastic Image Registration Versus Speckle Tracking for 2-D Myocardial Motion Estimation: A Direct Comparison In Vivo

Despite the availability of multiple solutions for assessing myocardial strain by ultrasound, little is currently known about the relative performance of the different methods. In this study, we sought to contrast two strain estimation techniques directly (speckle tracking and elastic registration) in an in vivo setting by comparing both to a gold standard reference measurement. In five open-chest sheep instrumented with ultrasonic microcrystals, 2-D images were acquired with a GE Vivid7 ultrasound system. Radial (ε_RR), longitudinal (ε_LL), and circumferential strain (ε_CC) were estimated during four inotropic stages: at rest, during esmolol and dobutamine infusion, and during acute ischemia. The correlation of the end-systolic strain values of a well-validated speckle tracking approach and an elastic registration method against sonomicrometry were comparable for ε_LL (r=0.70 versus r=0.61 , respectively; p=0.32) and ε_CC (r=0.73 versus r=0.80 respectively; p=0.31). However, the elastic registration method performed considerably better for ε_RR (r=0.64 versus r=0.85 respectively; p=0.09). Moreover, the bias and limits of agreement with respect to the reference strain estimates were statistically significantly smaller in this direction (p <; 0.001). This could be related to regularization which is imposed during the motion estimation process as opposed to an a posteriori regularization step in the speckle tracking method. Whether one method outperforms the other in detecting dysfunctional regions remains the topic of future research.