THE DIRECT ESTIMATION OF SOUND SPEED USING PULSE-ECHO ULTRASOUND

A method for the direct estimation of the longitudinal speed of sound in a medium is presented. This estimator derives the speed of sound th rough analysis of pulse-echo data received across a single transducer array following a single transmission, and is analogous to methods use d in exploration seismology. A potential application of this estimator is the dynamic correction of beamforming errors in medical imaging th at result from discrepancy between the assumed and actual biological t issue velocities. The theoretical basis of this estimator is described and its function demonstrated in phantom experiments. Using a wire ta rget, sound-speed estimates in water, methanol, ethanol, and n-butanol are compared to published values. Sound-speed estimates in two speckl e-generating phantoms are also compared to expected values. The mean r elative errors of these estimates an all less than 0.4%, and under the most ideal experimental conditions are less than 0.1%. The relative e rrors of estimates based on independent regions of speckle-generating: phantoms have a standard deviation on the order of 0.5%. Simulation r esults showing the relative significance of potential sources of estim ate error art: presented. The impact of sound-speed errors on imaging and the potential of this estimator for phase aberration correction an d tissue characterization are also discussed. (C) 1998 Acoustical Soci ety of America. [S0001-4966(98)03711-4].