Invited Speaker

Systems and Biomedical Applications of Optoacoustic Tomography
Alexander A. Oraevsky
USA

Optoacoustic tomography we proposed 15 years ago is presently emerging as useful platform for clinical and preclinical applications, including cancer biology, angiography, neurology, cardiology and real-time monitoring of drug efficiency and therapeutic interventions. Recently, we developed and tested in vivo a three-dimensional optoacoustic tomography system combining advantages of pulsed optical spectroscopy and high-resolution ultrasonic detection. The system was demonstrated to produce high-contrast 3D maps of optical absorbance through the whole body of an animal with resolution better than 0.5 mm. Much smaller tissue structures and microvessels can be visualized in case of sufficient contrast. An ultrawide-band of ultrasonic frequencies present in optoacoustic signals contains wealth of information, which can be revealed through proper filtering and post-processing. We demonstrated that either larger anatomy, such as organs or major vessels, or the smaller structures (kidney medullas, ovarian arteries or brain cortex vasculature) and even microvasculature can be visualized depending on methods of signal and image processing. Figure below shows exemplary images.

The endogenous imae contrast is based on the optical absorption of hemoglobin and oxy-hemoglobin, the main chromophores of blood in the near-infrared spectral range. Visualization of these chromophores at different optical illumination wavelengths provides not only anatomical information on tissue and vasculature, but also can be used to generate functional maps of blood concentration and its oxygen saturation. This system is useful as a tool for molecular imaging. As an exemplary demonstration, it was also used to generate molecular images of malignancy-related protein receptors in a xenograft tumor developed from a cluster of BT474 breast cancer cells. Acquisition of the latter images was facilitated by the use of gold nanorods covalently conjugated to an antibody raised against HER2/neu antigens. An exceptionally strong and tunable optical absorption in gold nanorods followed by effective energy conversion into heat makes these nanoparticles a superior optoacoustic contrast agent. Administration of these conjugates into mice resulted in an enhanced contrast of adenocarcinoma tumors relative normal tissues. Optoacoustic tomography enhanced with contrast agents based on nanotechnology has the potential to become a useful molecular imaging modality for preclinical research. Translation of this technology to clinic is ongoing. The first clinical application being developed is the diagnostic imaging of breast cancer. Results of a pilot clinical study will be presented.


Figure.Projections of 3D optoacoustic tomography images of a live nude mouse showing vasculature (left), internal organs and bifurcating aorta (second from left), microvasculature of the spine and the descending aorta (second from right), and the brain cortex vasculature (right).

In summary, this multidisciplinary presentation will review basic principles and applications of the optoacoustic tomography as enabling technology for preclinical research and clinical practice.