Mesoscopic imaging of fluorescent proteins using multi-spectral optoacoustic tomography (MSOT)

Noninvasive imaging of biological tissues using visible and near-infrared light may provide numerous insights into the underlying morphology or tissue function using a great variety of contrast and probing mechanisms. Nevertheless, mesoscopic-scale (i.e 1mm-1cm sized) living organisms remain largely inaccessible by current optical imaging methods. Depending on the optical properties of a particular object, light diffusion can significantly limit the resolution that can be achieved at depths beyond several hundred microns. To enable in-vivo optical contrast imaging of many important model organisms, such as insects, worms and similarly sized biological specimens, we have developed a multi-spectral optoacoustic tomography technique for high-resolution imaging of optically diffusive organisms and tissues. The method is capable of imaging at depths from sub-millimeter up to a centimeter range with a scalable spatial resolution on the order of magnitude of a few tenths of microns. Furthermore, we show for the first time that the technique is capable of resolving spatial distribution of fluorescent proteins inside intact opaque organisms, thus overcoming depth limitations of current fluorescence microscopy techniques.