Noninvasive Evaluation of Spatial Distribution of Local Instantaneous Strain Energy in Heart Wall

Abstract

For the noninvasive diagnosis of heart disease based on the acoustic characteristics of the heart muscle, we have developed a new method1 for accurately tracking the movement of the heart wall. By this method, a velocity signal of the heart wall with a small amplitude of less than 10 µm on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected with sufficient reproducibility in the frequency range up to several hundred Hertz continuously for periods of about ten heartbeats. The method has been applied to multiple points preset in the left ventricular (LV) wall along the ultrasonic beam² so that the spatial (depth) distributions of the velocity at these points are simultaneously obtained. From the resultant velocity signals, the motion of the heart wall is divided into the following two components: parallel global motion of the heart wall and the change in myocardial layer thickening at each depth across the LV wall during myocardial contraction/relaxation. In this paper, from the local change in thickness, spatial distribution of instantaneous strain energy generated and reserved in myocardium is noninvasively evaluated. This new approach offers potential for research on noninvasive acoustical diagnosis of myocardial local motility, that is, the myocardial layer function in the ventricular wall.