Block Matching Based Speckle Tracking Echocardiography: Clinical Applications and Research Outlook in a Deep Learning Context.

Speckle tracking echocardiography (STE) is effective in assessing cardiac dysfunction in high-risk populations for heart failure. As a fundamental STE technology, speckle tracking methods have been studied for nearly two decades. Over the past decade, the rapid development of AI has led to increasing interest in deep learning-based speckle tracking methods which require large annotated datasets for training. However, the challenge of manually annotating speckle regions in echocardiograms hinders the clinical deployment of those deep learning methods, thereby maintaining the indispensability of traditional speckle tracking methods. This paper presents a clinically applicable speckle tracking method, bidirectional block matching (BiDiBM), which introduces several novel processes to enhance the tracking accuracy and robustness of traditional BM methods. We evaluated BiDiBM for myocardial longitudinal strain (MLS) on an open-source synthetic echocardiographic dataset across four scenarios, comparing its strain measurements against the gold standard using the root mean square error (RMSE) and the zero-lag point (ZERO-LAG) of cross-correlation functions. Mean RMSE values across scenarios ranged from 1.0576 ± 0.2734% to 1.2812 ± 0.4703%, with corresponding ZERO-LAG values ranging from 0.8889 ± 0.1534 to 0.9484 ± 0.0399. In comparison experiments, BiDiBM achieved superior accuracy and efficiency over the conventional BM and the deep-learning comparators. Additionally, we performed a small real-world validation, in which BiDiBM tracked speckle points, and the derived MLS curves had physiologically consistent morphologies and trends on expert review. Overall, results indicate the BiDiBM method exhibits robust accuracy and reliability, thereby confirming its suitability for clinical STE applications and establishing a practical foundation for deploying deep learning-based methods in clinical settings.