The speed of sound (SoS) inside tissue depends on tissue composition and is therefore a diagnostic marker for disease that affects tissue composition. Conventional pulse-echo ultrasound reconstructs the location of acoustic reflectors inside the tissue based on the round-trip propagation time of the echoes. Computed Ultrasound Tomography in Echo mode (CUTE) goes beyond that: it senses the phase shift of local echoes when detected under varying insonification and detection angles. This echo phase shift is related to the changing round-trip time representing line integrals of SoS, and thus the spatial distribution of SoS can therefore be reconstructed by solving the corresponding inverse problem. The Figure shows a typical example of combined conventional ultrasound (left, shows the echo intensity) and CUTE (right side) in the abdomen: The different SoS of different tissue layers are nicely resolved.
