Biological & Soft Matter Seminar: Solving the Inverse Problem in Biophotonics: From Diffuse Light to Intrinsic Tissue Parameters
Prof. Dror Fixler, a member of the BioSoft Center and Professor at the School of Biomedical Engineering, TAU
Abstract:
Optical spectroscopy in biological tissues is fundamentally governed by multiple scattering, depth-dependent photon pathlength distributions, and heterogeneous absorption. While molecular contrast mechanisms are often well understood at the microscopic scale, translating measured diffuse optical signals into intrinsic tissue parameters remains a central inverse problem in biophotonics. In highly scattering media, the detected spectrum is not a direct representation of chromophore absorption or tissue structure, but rather the outcome of complex radiative transport.
In this lecture, I will present a quantitative framework for parameter extraction in strongly scattering biological media. Starting from the radiative transport equation and its diffusion approximations, I will discuss the ill-posed nature of recovering absorption and reduced scattering coefficients from reflectance measurements, and outline practical strategies for improving identifiability and robustness.
Methodological advances including iso-pathlength approaches, spectral constraint-based inversion, polarization-sensitive measurements, and model-based fitting will be presented as tools to decouple absorption and scattering contributions under realistic biological conditions. Representative case studies will illustrate the transition from qualitative optical contrast to quantitative tissue characterization, with emphasis on reproducibility, cross-subject comparability, and physiological interpretability.
Finally, I will discuss future directions toward unified inversion frameworks that integrate spectral, temporal, and structural information, positioning tissue optics as a predictive and quantitative discipline within biological spectroscopy.
