Spatial covariance analysis for tissue harmonic imaging

Spatial covariance contains important information in the context of correlation-based correction of sound velocity inhomogeneities. Previous work was primarily based on spatial covariance analysis for linear imaging. In this paper, we extend the analysis to tissue harmonic imaging. Specifically, we investigate effects of the signal-to-noise ratio (SNR) and sound velocity inhomogeneities on spatial covariance. It is shown that linear imaging at f₀ and second harmonic imaging at 2f₀ have similar spatial covariance at high SNRs, regardless the presence of sound velocity inhomogeneities. At low SNRs, however, spatial covariance of tissue harmonic imaging is significantly affected. It is concluded that the linear signal is more suitable for correlation-based correction of sound velocity inhomogeneities despite the fact that tissue harmonic imaging generally has improved image quality over linear imaging