Broadband absorption spectroscopy in turbid media by combined frequency-domain and steady-state methods

A technique for measuring broadband near-infrared absorption spectra of tur bid media that uses a combination of frequency-domain (FD) and steady-state (SS) reflectance methods is presented. Most of the wavelength coverage is provided by a white-light SS measurement, whereas the FD data are acquired at a few selected wavelengths. Coefficients of absorption (mu (a)) and redu ced scattering (mu (s)') derived from the FD data are used to calibrate the intensity of the SS measurements and to estimate mu (s)' at all wavelength s in the spectral window of interest. After these steps are performed, one can determine mu (a) by comparing the SS reflectance values with the predic tions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combi ned SSFD technique, agree well with expected reference values. All measurem ents can be performed at a single source-detector separation distance, redu cing the variations in sampling volume that exist in multidistance methods. The technique uses relatively inexpensive light sources and detectors and is easily implemented on an existing multiwavelength FD system. (C) 2000 Op tical Society of America OCIS codes: 170.1470, 170.4090, 170.5280, 170.7050 .