Minimization of Displacement Estimation Bias Due to High Amplitude-Reflections Using Envelope-Weighted Normalization

Abstract

In elastography, displacement estimation is often performed using cross-correlation-based techniques, assuming fully-developed, homogeneous speckle. In the presence of a local, large variation in echo amplitude, such as a reflection from a vessel wall, this assumption does not hold true, resulting in a biased displacement estimate. Normalizing the echo by its envelope before displacement estimation reduces this effect at the cost of larger jitter errors. An algorithm is proposed to reduce amplitude-dependent bias in displacement estimates while avoiding a large increase in the jitter error magnitude. The algorithm involves ‘Envelope-Weighted Normalization’ (EWN) of echo data before displacement estimation. A parametric analysis was conducted to find the optimum parameters with which this technique could be implemented. The EWN technique was found to significantly reduce the rms error of the displacement estimates, showing the greatest improvements when utilizing longer window lengths and higher ultrasonic frequencies.