Optical Analysis of biological media - continuous wave diffuse spectroscopy

Abstract: The main topic of this thesis is real-time quantification of relevant chromophores and light scattering elements in biological media. The presented methods and instrumentation are based on continuous wave (steady-state) optical measurements of (a) spatially-resolved diffuse reflectance from bulk media and (b) combined spatially-resolved and goniometric measurements of re-emitted light from thin samples. These two configurations address applications for non-invasive medical diagnostics (optical biopsy), and in vitro diffuse spectroscopy of turbid samples (e.g. whole blood analysis and immunoassays), respectively. The physical basis of light-tissue interaction, i.e. absorption and scattering, is discussed, as well as various theoretical models for light propagation in turbid biological media, e.g. Monte Carlo simulations, diffusion theory, and the adding-doubling method. The optical properties are extracted from the measurements using multivariate calibration and analysis techniques. Therefore, a general introduction to such methods is also included, e.g. principal component analysis, multiple polynomial regression, and Newton-Raphson prediction algorithms. Finally, some of the prototype instrumentation developed during the project is presented, e.g. a fiber probe system, an integrating sphere setup, and a hybrid goniometric/spatially-resolved system.