Crossambiguity and wavelet processing in ultrasound elasticity imaging

Time-scaling the rf echo signals commensurately with the strain in tissue allows matching of pre- and post-deformation echo signal peaks and can result in an improved elasticity image noise. The technique requires an estimate of the tissue strain for the application of the appropriate time scaling, but this parameter unknown a priori. We have applied a wideband crossambiguity function, a generalization of the crosscorrelation function with two variables: time-shift and time- scale; this operation can also be interpreted as a wavelet transform. Time scaling is achieved using multi-rate conversion techniques. Results from a vessel phantom experiment show that improved time-shift estimates can be obtained using time-scaling. The improvement is a function of the observation window length and tissue strain. Although multi-rate processing is computationally intensive, optimization of the processing time using a cross-wavelet transform algorithm is under investigation