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28 June 1994 Absorption spectra of a chromophore in highly scattering media
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Frequency domain spectroscopy provides a quantitative measure of the optical properties, namely (mu) a and (mu) s' coefficient spectra, of multiply scattering, macroscopically homogeneous media or tissue. The diffusion model for photon transport provides the theoretical framework for the analytical expressions of the optical properties. Experimentally, we intensity modulated (60 MHz) a light emitting diode, which emits between 620 - 700 nm. From data sets of relative phase shifts and average intensity at different source- detector separations, we calculated on the basis of the analytical expressions a wavelength resolved absorption (mu) a ((lambda) ) and scattering (mu) s' ((lambda) ) coefficient spectrum. The test material was methylene blue, whose absorption spectrum (maximum 656 nm) closely matches the wavelength profile of the diode source. The multiply scattering, macroscopically homogeneous medium for dissolving the methylene blue was provided by a diluted fat emulsion, Liposyn III. The concentrations of both the absorbing and scattering materials were adjusted to correspond to ranges typical of (mu) a and (mu) s' in tissues. We obtained quantitative agreement between the measured (mu) a ((lambda) ) in the scattering medium and a control solution measured in a spectrophotometer under non-scattering conditions.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sergio Fantini, Maria-Angela Franceschini, Joshua B. Fishkin, William W. Mantulin, and Enrico Gratton "Absorption spectra of a chromophore in highly scattering media", Proc. SPIE 2100, Cell and Biotissue Optics: Applications in Laser Diagnostics and Therapy, (28 June 1994);

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