FLUORESCENCE-LIFETIME DETERMINATION IN TISSUES OR OTHER SCATTERING MEDIA FROM MEASUREMENT OF EXCITATION AND EMISSION KINETICS

Measurements of nanosecond and subnanosecond fluorescence lifetimes ar e restricted to dilute, nonscattering systems since excitation and emi ssion photon times of flight significantly affect measured fluorescent decay kinetics. We provide the theoretical rationale for frequency-do main measurements of phase-shift and amplitude demodulation made at ex citation and emission wavelengths for direct determination of lifetime s in tissues and other scattering media. We confirm our analytical exp ressions using standard laser dyes such as 3,3'-diethylthiatricarbocya nine iodide, IR-125, and IR-140 in polystyrene suspensions with simila r scattering properties as tissues. Our results have significant impli cation for lifetime-based spectroscopy in tissues and other scattering media. (C) 1996 Optical Society of America