Normalized transillumination of fluorescent proteins in small animals.

We investigated the capacity of normalized transillumination methods in imaging fluorescent proteins in visible light, in phantoms and in live mice. We demonstrate significant imaging improvements over epi-illumination imaging, as commonly applied today. Of particular importance is the significant betterment in contrast achieved, due to minimization of the influence of autofluorescence and the enhancement of depth sensitivity compared to epi-illumination imaging. Although normalized transillumination does not match the accuracy and quantification capacity of tomographic imaging, it nevertheless attains key advantages over other planar optical imaging methods while preserving implementation simplicity. Due to the balance achieved between simplicity and accuracy, normalized transillumination approaches could serve as an important alternative molecular imaging method.