Preliminary Study on Ultrasonic Visualization of Myocardial Contraction and Relaxation Based on Local Strain Rate

Ultrasonic visualizations of the contraction and relaxation properties of the myocardium have been developed to detect an abnormality of the myocardial function noninvasively. The strain rate (SR) measurements have been used to detect the post systolic shortening owing to ischemia. However, the erroneous estimation of the SR sometimes causes a false detection of the contraction or relaxation of the myocardium. In the present paper, it was confirmed through simulations that the estimation error of the velocity in the beam direction caused by the lateral displacement of the myocardium negatively affects the visualization of the contraction and relaxation based on the estimated SR. Moreover, the law of error propagation in the local SR measurement was confirmed by comparing the correlation value between the velocities for calculating the local SR with the actual value. In the simulations, the correlation value derived from the law of error propagation corresponded with the actual correlation value in the local SR measurement especially when the absolute value of the true SR was not large. Therefore, the law of error propagation held in the local SR measurement. Moreover, the correlation value related to the overlapped region of the velocity estimation windows. These results indicated that the precision of the local SR measurement could be estimated based on the law of error propagation. The contraction and relaxation of the myocardium would be visualized without the false detection using the estimated precision.