FREQUENCY-DOMAIN MEASUREMENTS OF PHOTON MIGRATION IN TISSUES

We report the use of frequency-domain (FD) measurements to characterize time-dependent migration of 620-740 nm photons in tissues, in particular arm and finger. The time dependence of the re-emerged light appears to be characterized by a delay time which depends on path length and detector geometry, a transient-time spread which appears to depend on sample homogeneity, and an exponential decay time which depends on sample absorbance and/or path length. The time delay is revealed by a phase angle exceeding 90°, which is not explainable for directly initiated multi- or single-exponential processes. The transit-time spread is revealed by a frequency-dependent decrease in modulation which is more rapid than for an exponential decay. Potential clinical uses of the FD photon migration measurements are discussed. © 1990.