The speed of sound (SoS) inside tissue depends on tissue composition and is therefore a promising diagnostic marker for disease progression. With the invention of computed ultrasound tomography in echo-mode (CUTE) we are now able to achieve a contrast and spatial resolution sufficient for clinical imaging. Pulse-echo ultrasound reconstructs acoustic reflectors inside the tissue based on the acoustic round-trip time of the echoes (axial resolution) and focusing (transversal resolution). CUTE is based on sensing the phase shift of local echoes when insonifying the tissue under various different angles using steered ultrasound transmissions. The echo phase shift is related to the changing round-trip time and thus to path integrals of SoS, and the spatial distribution of SoS can therefore be reconstructed by solving the inverse problem. The Figure shows a typical example of combined conventional ultrasound (left, shows the echoes) and real-time CUTE (right side) in the abdomen: The different SoS of different tissue layers are nicely resolved (s: skin, sf: subcutaneous fat, m: muscle, pf: postperitoneal fat, l: liver). In addition, we are active in further developing through transmission ultrasound tomography, which has been shown by other groups to provide high contrast images of the breast for cancer diagnosis.
