Fig. 1: Computed ultrasound tomography in echo mode (CUTE) workflow.

a Tissue is insonified by sequentially transmitting a set of wavefronts with varying steering angles. We use delay-and-sum beamforming and coherent compounding on the recorded radio-frequency signals to reconstruct synthetically focused and steered ultrasound images for transmit (Tx) angles ranging from −55° to 55° relative to the axial direction. Orange downwards-pointing arrows indicate the orientation of these Tx wavefronts. b We combine all these images to form a conventional echo-intensity B-mode image. c For CUTE, each image in (a) is decomposed via spatial frequency filtering into a set of images corresponding to different receive (Rx) steering angles (orange upwards-pointing arrows). These images are characterized by the mid angle (Mid) between Tx and Rx angles (dashed orange lines). Tx-Rx angle pairs with identical mid-angle provide well-correlated images. d We extract the spatial distribution of echo phase shifts from such well-correlated image pairs. We obtain a phase-shift map per mid angle and Tx-Rx angle difference (Diff). e Tissue speed of sound (SoS) is estimated from phase-shift maps solving a linear inverse problem. f The result is displayed together with the B-mode image in the SuperSonic® MACH® 30 ultrasound system (picture provided by SuperSonic Imagine® and adapted with permission). Although CUTE uses complex radio-frequency images in steps (a) and (c), here we show echo-intensity images for illustrative purposes.