Multispectral guided fluorescence diffuse optical tomography using upconverting nanoparticles

We report on improved image detectability for fluorescence diffuse optical tomography using upconverting nanoparticles doped with rare-earth elements. Core-shell NaYF4:Yb3+/Er3+@NaYF4 upconverting nanoparticles were synthesized through a stoichiometric method. The Yb3+/Er3+ sensitizer-activator pair yielded two anti-Stokes shifted fluorescence emission bands at 540 nm and 660 nm, here used to a priori estimate the fluorescence source depth with sub-millimeter precision. A spatially varying regularization incorporated the a priori fluorescence source depth estimation into the tomography reconstruction scheme. Tissue phantom experiments showed both an improved resolution and contrast in the reconstructed images as compared to not using any a priori information.