Evaluation of a nonlinear simultaneous compressibility and mass density reconstruction algorithm in contrast to established linear ultrasound imaging approaches

While established linear pulse-echo ultrasound imaging concepts like synthetic aperture (SA) focusing and delay-and-sum (DAS) beamforming solely image tissue features under single scattering, nonlinear reconstruction methods have been proposed to compute quantitative maps of the tissue´s material parameters (e.g. compressibility, mass density, speed of sound) under multiple scattering. In the present contribution, we apply a previously proposed nonlinear simultaneous compressibility and mass density reconstruction algorithm and investigate numerically the image reconstruction quality in contrast to linear SA under cylindrical wave (cw) excitation and linear DAS under plane wave (pw) excitation. Using raw data acquired from a Shepp-Logan phantom (SLP) with typical soft tissue compressibility and mass density values, nonlinear reconstruction using cylindrical wave excitation provides high-resolution images with a mean magnitude of relative error of about 4.27% and 3.18% within a region of interest (ROI) in the compressibility and mass density image, outperforming the image quality reached under plane wave excitation. Applying identical raw data, SA and DAS with both predefined and adapted apodization weights yield less-detailed image reconstructions solely showing tissue boundaries. Furthermore, calculating full width at half maximum (FWHM) resolutions of all methods, the nonlinear approach mainly yields smaller axial and lateral resolutions in contrast to SA and DAS.