Imaging growth of thick engineered tissues with fluorescence diffuse optical tomography

Recent advances in tissue engineering (TE) aim to grow 3D volumes of tissue in bioreactor conditions. This has proved to be a difficult task thus far, notably due to the lack of non-invasive diagnostic tools to monitor the growth of a tissue and ensure its appropriate development. To fulfill part of this need, we currently develop a non-invasive imaging technique based on fluorescence diffuse optical tomography (FDOT) to image in 3D, via fluorescent tracers, processes relevant to tissue growth in a bioreactor. More particularly, here we are interested in imaging the formation of micro-blood vessels in tissue cultures grown on biodegradable scaffolds. Blood vessels are thought to play a fundamental role in tissue growth. Since a bioreactor possesses a known geometry (by design), we propose an FDOT configuration that uses fiber optics brought in contact with the boundary of the bioreactor to collect tomographic optical data. We describe an optical fibers-based set-up and experimental measurements that demonstrate the possibility of localizing a fluorophore-filled 500µm capillary immersed in a scattering medium contained in a cylindrically-shaped glass tube. These conditions are representative of experiments to be carried on real tissue cultures. In our particular implementation, time-resolved scattering-fluorescence measurements are made via time-correlated single photon counting. Numerical constant fraction discrimination applied to our time-resolved data allows to extract primary localization information.