Comparison of linear and nonlinear unidirectional imaging approaches in ultrasound breast imaging

In ultrasound imaging, strong variations in the tissue´s acoustic impedance give rise to multiple scattering. While these are not accounted for in established reconstruction concepts like linear synthetic aperture (SA) focusing and delay-and-sum (DAS) beamforming, nonlinear diffraction tomographic reconstruction algorithms have been developed to reconstruct an object´s inner structure under multiple scattering. In this contribution, we employ a proposed iterative nonlinear compressibility reconstruction algorithm to evaluate the potential image reconstruction quality numerically in contrast to SAand DAS reconstructions. Using the same simulated unidirectional pulse-echo measurements acquired from a numerical breast phantom with realistic compressibility values, the nonlinear approach provides reconstructions with relative errors of about 1.54% within the diagnostically significant region, whereas SA and DAS yield artifact-affected reconstructions mainly showing tissue boundaries with less detail. Moreover, applying simulated measurements acquired from a numerical wire phantom, we validate the potential axial and lateral resolutions of all three methods. The -6 dB axial resolution of the nonlinear approach outperforms those obtained by SA and DAS; the nonlinear approach and SA provide similar -6 dB lateral resolutions outperforming DAS.