Optoacoustic and Ultrasound Imaging

Medical imaging provides invaluable structural and functional information of the inside of the body. Ultrasonography (US) is broadly available due to its portability, safe use, real-time display, and low price. On the downside, the classical contrast mechanism—echo intensity—restricts its diagnostic value to limited scenarios. At the Optoacoustic and Ultrasound Imaging Team, we develop novel US-based imaging modes aimed at combining the availability and flexibility of US with complementary diagnostic power.

• Opto (or photo-) acoustic imaging (OA) maps the optical absorption inside tissue with the spatial resolution of US by combining pulsed laser irradiation with acoustic detection. OA is promising in, e.g., the diagnosis and monitoring of vascular diseases, arthritis, and cancer.

• Computed Ultrasound Tomography in Echo mode (CUTE) maps the tissue’s speed of sound (SoS) which is a promising marker for disease that influences the tissue’s composition. Together with our collaborators and the Inselspital (Prof. Dr. med. Annalisa Berzigotti) we have shown that CUTE detects fatty liver disease

Quantitative Spectral Optoacoustic Imaging

Spectral OA imaging exploits the difference in the absorption spectra of oxy- and deoxyhemoglobin for estimating the oxygen saturation inside small blood vessels, a diagnostic marker in tumors, ischemia, and would healing.

A central issue for achieving quantitative results is the spectral coloring of the irradiating laser light by background tissue. In our research on quantitative deep OA imaging, we therefore investigate techniques to correct for the spectral distortion of the recorded OA signals.  

Optoacoustic Clutter Reduction

Our team focuses on the combination of OA with classical US systems, where the irradiation optics is integrated with the ultrasound detector in a handheld probe. A drawback of this epi-illumination is the reverberation of OA signals inside the acoustically scattering tissue. We develop techniques that reduce this noise and thereby increase the achievable imaging depth, among them localized vibration tagging (LOVIT).

Speed of Sound Imaging

Left: conventional echo ultrasound provides gray-scale images of echo intensity representing tissue microstructure. Right: a map of the spatial distribution of speed of sound (SoS) reveals differences in tissue composition, here skin (s), subcutaneous fat (sf), muscle (m) muscle, extraperitoneal fat (pf), and liver (l).

The speed of sound (SoS) inside tissue depends on tissue composition and is 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.