Expanding aliasing limit in measurement of tissue velocity using autocorrelation method

Autocorrelation using in-phase and quadrature (IQ) signals suffers from aliasing when the velocity of rapidly moving tissue, such as the heart wall, is measured. In the present study, a simple method was proposed to expand the aliasing limit. In the proposed method, the velocity difference between two successive frames (corresponding to acceleration) of tissue was also estimated directly from IQ signals. When aliasing occurs in the velocity in the current frame, which was estimated from IQ signals, the velocity in the current frame was corrected by adding the velocity difference to the velocity in the previous frame. Using this procedure, the velocity can be estimated if the difference between velocities in the current and previous frames is less than the aliasing limit. The velocity of the posterior heart wall in the longitudinal-axis view of about 0.08 m/s could be estimated under the aliasing limit of the conventional autocorrelation method of 0.047 m/s. Myocardial velocity over the conventional aliasing limit could be measured by the proposed method.