Hyperspectral in vivo two-photon microscopy of intrinsic contrast.

In vivo two-photon imaging of intrinsic contrast can provide valuable information about structural tissue elements such as collagen and elastin and fluorescent metabolites such as nicotinamide adenine dinucleotide. Yet low signal and overlapping emission spectra can make it difficult to identify and delineate these species in vivo. We present a novel approach that combines excitation scanning with spectrally resolved emission two-photon microscopy, allowing distinct structures to be delineated based on their characteristic spectral fingerprints. The amounts of intrinsic fluorophores present in each voxel can also be evaluated. We demonstrate our method using in vivo imaging of nude mouse skin.