OPTIMAL PROBE GEOMETRY FOR NEAR-INFRARED SPECTROSCOPY OF BIOLOGICAL TISSUE

The results of this study clarify the influence of probe geometry on s pectroscopic measurements obtained from the surface of a turbid biolog ical tissue. We show that the transition between the measurement of th e predominantly backward-propagating and the predominantly forward-pro pagating photon fluxes is marked by the separation between the source probe and the detector probes at which the dependence of the fluence o n small changes in scattering coefficient vanishes. This is the probe separation at which a variable scattering background has the least inf luence on the measurement of optical absorption in turbid materials. E stimates of the optimum probe spacing for typical values of absorption and scattering coefficients of soft tissue in the near-infrared spect ral region (800-2500 nm) are derived from an analytical solution of th e diffusion equation. The estimates were verified by Monte Carlo simul ations and experiments on particle suspensions with optical properties similar to those of skin tissue. (C) 1997 Optical Society of America.