Maximum-likelihood approach to strain imaging using ultrasound

A maximum-likelihood (ML) strategy for strain estimation is presented as a framework for designing and evaluating bioelasticity imaging systems. Conce pts from continuum mechanics, signal analysis, and acoustic scattering are combined to develop a mathematical model of the ultrasonic waveforms used t o form strain images. The model includes three-dimensional (3-D) object mot ion described by affine transformations, Rayleigh scattering from random me dia, and 3-D system response functions. The likelihood function for these w aveforms is derived to express the Fisher information matrix and variance b ounds for displacement and strain estimation. The ML estimator is a general ized cross correlator for pre- and post-compression echo waveforms that is realized by waveform warping and filtering prior to cross correlation and p eak detection. Experiments involving soft tissuelike media show the ML esti mator approaches the Cramer-Rao error bound for small scaling deformations: at 5 MHz and 1.2% compression, the predicted lower bound for displacement errors is 4.4 mu m and the measured standard deviation is 5.7 mu m. (C) 200 0 Acoustical Society of America. [S0001-4966(00)00903-6].