DEFORMATION MODELS AND CORRELATION-ANALYSIS IN ELASTOGRAPHY

Cross-correlation functions are derived with the purpose of determinin g how strain inhomogeneities affect the displacement estimates used in ultrasound-based elastography. Variations in the strain profile occur in most imaging situations and are caused by fluctuations in the stre ss field or elastic modulus of the sample. An analytical framework for developing signal processing strategies in elastography is described, and the Limitations of correlation-based methods for measuring displa cements in tissuelike media caused by static compression are emphasize d. This paper includes (1) an accurate approximation for an inverse co ordinate transformation that relates pre- and postcompression reflecti vity profiles of the media, (2) a derivation of the echo-signal cross- correlation function in media with deterministic or stochastic strain profiles; (3) mathematical and graphical descriptions of the consequen ces that nonuniformities in the strain profile impose upon the uncerta inty of displacement estimation; and (4) a demonstration of the advant ages of echo signal conditioning and ultrasonic-pulse shaping to reduc e the nonstationary effects that attenuate the cross-correlation peak and reduce the signal-to-noise ratio for displacement estimation. (C) 1996 Acoustical Society of America.