title: Direct characterization and removal of interfering absorption trends in two-layer turbid media.
abstract: We propose a method to isolate absorption trends confined to the lower layer of a two-layer turbid medium, as is desired in near-infrared spectroscopy (NIRS) of cerebral hemodynamics. Several two-layer Monte Carlo simulations of NIRS time series were generated using a physiologically relevant range of optical properties and varying the absorption coefficients due to bottom-layer, top-layer, and/or global fluctuations. Initial results showed that by measuring absorption trends at two source-detector separations and performing a least-squares fit of one to the other, processed signals strongly resemble the simulated bottom-layer absorption properties. Through this approach, it was demonstrated that fitting coefficients can be estimated within less than +/- 2% of the ideal value without any a priori knowledge of the optical properties present in the model. An analytical approximation for the least-squares coefficient provides physical insight into the nature of errors and suggests ways to reduce them.
authors.affiliation: The Institute of Optics, University of Rochester, Rochester, New York 14627, USA.
authors.forename: Rolf B
authors.initials: RB
authors.lastname: Saager
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Berger
mesh_terms: D000042:Absorption; D000465:Algorithms; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008959:Models, Neurological; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*