Ultrasonic imaging of propagation of contraction and relaxation in the heart walls at high temporal resolution

Strain and strain rate imaging have been shown to be useful for the assessment of regional myocardial function. However, some of the mechanisms of transition in myocardial contraction/relaxation remain unclear. In this study, the RF echoes from the left ventricular (LV) wall were acquired in both the longitudinal-axis view and the apical view by scanning ultrasonic beams sparsely to improve the temporal resolution, and a frame rate of about 600Hz was realized. The phased tracking method was applied to multiple points in the heart wall to estimate the strain rate. The spatial distribution of the strain rate measured about every 2 ms showed the continuous transition in the myocardium. In the apical view, the propagation speed of contraction from the apex to the base side in the interventricular septum was found to be about 0.8 m/s. These results indicate the potential of this method in the estimation of the physiological function of the myocardium.