Ultrasonic scattering in deformed media and the effects on strain imaging

Acoustic properties of tissue-like media with stiff and soft scatterers were measured as a function of compressive strain up to 40%. Uniaxial strain measurements were analyzed to test the assumption that local properties of wave propagation and scattering are invariant under deformation. We found that echo spectra of gel media with soft scatterers varied significantly and predictably during compression. Specifically, centroids of Gaussian echo spectra were shifted to higher frequencies in proportion to the compressive strain applied up to 10%, and increased monotonically up to 49% at a rate depending on the scatterer size. The results explain why there is often more echo decorrelation produced in tissues than in commonly used graphite-gelatin test phantoms