Interstitial point radiance spectroscopy of turbid media

We present an optical technique, point radiance spectroscopy, to directly recover chromophore concentrations and the reduced optical scattering coefficient spectrum from continuous wave interstitial point radiance measurements at a single-source-detector separation in turbid, tissuelike media. The method employs a spectral algorithm to fit the relative radiance data, using the P3 approximation, at only two detection angles (0 degrees and 90 degrees). The spectral fitting algorithm is applied to simulated data of relative point fluence and relative point radiance data with added 1% noise and shows that even under realistic experimental conditions, only point radiance information is able to provide quantitative information regarding chromophore concentrations and scattering power at distances greater than two to three mean free paths from the source. Furthermore, experimental measurements in tissue-simulating phantoms demonstrate that dye concentrations and scattering parameters can be recovered to within similar to 10%. The developed point radiance technique bridges a technological gap between local surface reflectance and spatially resolved interstitial fluence methods in optical assessment of random media such as biological tissue.