Refraction-Aware Integral Operator for Speed-of-Sound Pulse-Echo Imaging

Speed-of-sound pulse-echo imaging denotes a set of promising techniques able to expand the diagnostic capabilities of medical ultrasound. Their objective is to recover a speed-of-sound map of soft tissue and use it as a biomarker for diseases that are difficult to detect using standard B-mode imaging. Such methods often rely on a specific linear operator based on straight-ray approximation to compute the local wave propagation time. Refraction effects are thus neglected, leading to potential artifacts in the reconstructed speed-of-sound maps. We propose in this paper a non-linear, iterative operator able to account for these effects with a low computational complexity. In order to assess the accuracy of the proposed operator, we first compare its predictions to the results of k-Wave simulations. A model based on the proposed operator is then deployed to recover speed-of-sound maps from simulated data. The results are compared to those obtained by a standard linear operator, and a mitigation of the reconstruction artifacts due to straight-ray approximation is observed. It implies in particular a reduction of the RMSE from 11.65 m/s to 7.08 m/s in a low-noise case.