TR-MUSIC inversion of the density and compressibility contrasts of point scatterers

Time-reversal imaging with multiple signal classification (TR-MUSIC) is a super-resolution ultrasound imaging method for detecting point scatterers. This algorithm assumes that there is no contrast between the density of the point targets and that of the background medium, and that ultrasound scattering is caused only by the compressibility contrast. We modify the TR-MUSIC algorithm to account for ultrasound scattering from point targets with both density and compressibility contrasts. In addition, we develop an inversion method for estimating the density and compressibility contrasts of point scatterers with known locations. This approach is an extension of the inversion method previously developed by Devaney et al. for estimating the scattering strengths of point targets that have no density contrasts relative to the background medium. We use numerical phantom data to demonstrate that our new TR-MUSIC inversion algorithm can reliably estimate the density and compressibility contrasts of point scatterers. The estimates of these properties could be used for distinguishing breast calcifications from other tissue scatterers.