REDUCTION OF SIGNAL DECORRELATION FROM MECHANICAL COMPRESSION OF TISSUES BY TEMPORAL STRETCHING - APPLICATIONS TO ELASTOGRAPHY

Elastography is based on the estimation of strain due to tissue compre ssion. Strain is computed from the estimates of time delays between ga ted precompression and postcompression echo signals. Time delay estima tes are obtained from the location of the peak of the crosscorrelation function between gated precompression and postcompression signals. It is of paramount importance to accurately estimate the time delays for good quality elastograms. A main source of time delay estimation (TDE ) error in elasticity imaging is the decorrelation of the echo signal as a result of tissue compression (decorrelation noise). The effect of decorrelation on the mean of the cross-correlation function and the c orrelation coefficient has been investigated. The expected value of th e cross-correlation function between the precompression and postcompre ssion signals was shown to be a filtered version of the autocorrelatio n function of the precompression signal. In this article, the effect o f temporal stretching of the postcompression echo signal on the crossc orrelation function will be investigated along the same line. The appl ied compression is assumed to be uniform; the decorrelations introduce d by the lateral and elevational tissue movements are ignored. The the ory predicts that if the postcompression echo signals are stretched be fore the TDE step, then for small strains, the cross-correlation funct ion very closely resembles the autocorrelation function. For larger st rains, correlation is improved if temporal stretching is applied. The theory is corroborated by results from simulation and homogeneous phan tom experiments. Thus, the decorrelation noise in elastograms can be r educed by temporal stretching of the postcompression signal. Copyright (C) 1997 World Federation for Ultrasound in Medicine & Biology.