Feature Tracking Algorithm for Circumferential Strain using High Frame Rate Echocardiography

This study aims to describe a feature tracking algorithm tailored to estimate circumferential strain on high frame rate ultrasound (HFR-US) images. The algorithm used the Hungarian assignment algorithm for tracking a basic feature descriptor. A second order Kalman model was used to recursively describe regional myocardial displacement along the myocardial contour, and the strain was calculated using these displacements. HFR-US images at 360 fps were acquired from a patient with left bundle branch block (LBBB) in the parasternal short axis view with a biventricular (BiV) pacer turned off and on. There was a large variation in the onset and end of mechanical contraction for each individual myocardial region when the BiV pacer was turned off. The variation reduced immediately when the BiV pacer was turned on. The presented algorithm can estimate circumferential strain using high frame rate ultrasound images. The circumferential strain does suffer from high intra-and inter-operator variance due to the lack of landmarks making it difficult to reproduce results. However, as circumferential and longitudinal strain offer two different, but somehow interrelated, descriptors of complex mechanical movement of the heart. The observed variance reduction may be indicative for a positive BiV response in LBBB patients.