A Study on Noninvasive Ultrasonic Measurement of Minute Mechanical-Excitation Wave-front Propagation in Human Myocardial Tissue and Its Visualization

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Complexity of the cardiac contraction sequence is still not fully understood because the dynamic mechanical excitation process, which directly correlates with contraction, cannot be accurately measured based on the electro-magnetic phenomena. By developing a noninvasive novel imaging modality with high temporal and spatial resolutions, the present study shows that the propagation of the mechanical wave-front occurs at the beginning of cardiac contraction sequence for the first time (about 60 ms prior to the ordinarily accepted onset time of the contraction). From the apical side of the interventricular septum, a minute velocity component with an amplitude of several tenth micrometers is generated and it propagates from the apex to the base of the posterior wall, and then from the base to the apex of the septum, with a propagation speed of 3-9 m/s. This dynamic measurement modality is also applicable to various tissues in biology.