Polar-Space Frequency-Domain Filtering for Improved Pulse-echo Speed of Sound Imaging with Convex Probes

Imaging the spatial distribution of the speed of sound (SoS) is essential for enhancing ultrasound image formation and tissue characterization. While common mid-angle (CMA) tracking has improved reconstruction accuracy in linear probes, its application to convex probes has been limited despite their advantages in imaging depth and penetration. This study introduces a novel polar-space frequency-domain filtering approach for CMA tracking in convex probes. By expressing beamformed radiofrequency (RF) data in polar coordinates and applying low-pass filtering in the spatial frequency domain, our method preserves axial oscillations that align with the element directivity of convex probes. Results show that the proposed approach enhances the agreement between the simulated and theoretical phase shift, consequently improving the reconstruction accuracy. From a practical standpoint, our approach operates on the post-beamformed RF and does not require access to raw channel data, making it compatible with a wider range of commercial ultrasound scanners.