Characterization of non-homogeneous turbid media with spectroscopic radiance measurements from a single location

Optical techniques are under exploration to investigate and monitor tissue before, during and after therapies such as laser interstitial thermal therapy and photodynamic therapy. Point radiance spectroscopy reveals a potential wealth of information via directional radiance measurements, compared to isotropic fluence data, in decoupling the absorption and scattering contributions to attenuation. This study extends those findings to spatially heterogeneous systems with an approach that measures local light behaviour directly rather than calculating optical property values. This approach involves identifying chromophores present in local non-homogeneities by characterizing spectral differences in radiance measurements. The method also detects optical asymmetry in the medium by comparing opposing angular spectra. Analysis of the asymmetry can distinguish a homogeneous state from a system that contains a spatial non-homogeneity and identify the side of the radiance probe on which it lies. Monte Carlo simulations reinforce the findings and explain the mechanisms behind trends in sensitivity and capacity.