Direct characterization and removal of interfering absorption trends in two-layer turbid media

J Opt Soc Am A Opt Image Sci Vis. 2005 Sep;22(9):1874-82. doi: 10.1364/josaa.22.001874.


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.

MeSH terms

  • Absorption
  • Algorithms*
  • Brain / physiology*
  • Brain Mapping / methods*
  • Computer Simulation
  • Humans
  • Image Enhancement / methods*
  • Image Interpretation, Computer-Assisted / methods*
  • Models, Neurological*
  • Nephelometry and Turbidimetry / methods*
  • Spectroscopy, Fourier Transform Infrared / methods*