Measurement of the fluorescence lifetime in scattering media by frequency-domain photon migration.

A method is presented to determine fluorescence decay lifetimes within tissuelike scattering media. Fluorescence lifetimes are determined for micromolar concentrations of the dyes 3,3'-Diethylthiatricarbocyanine Iodide and Indocyanine Green by frequency-domain investigations of light propagating in turbid media. Dual-wavelength photon-migration measurements that use intensity-modulated sources at excitation and emission wavelengths of the fluorophores provide optical parameters of the media as well as fluorescence properties of the dyes. The deduction of fluorescence lifetimes requires no calibration with reference fluorophores, and the results are shown to be independent of dye concentration.