A technique for measuring broadband near-infrared absorption spectra of turbid 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 (μ<sub><i>a</i></sub>) and reduced scattering (μ<sup>′</sup><sub><i>s</i></sub>) derived from the FD data are used to calibrate the intensity of the SS measurements and to estimate μ<sup>′</sup><sub><i>s</i></sub> at all wavelengths in the spectral window of interest. After these steps are performed, one can determine μ<sub><i>a</i></sub> by comparing the SS reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue <i>in vivo</i>, derived with the combined SSFD technique, agree well with expected reference values. All measurements can be performed at a single source–detector separation distance, reducing 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.
© 2000 Optical Society of America
(170.1470) Medical optics and biotechnology : Blood or tissue constituent monitoring
(170.4090) Medical optics and biotechnology : Modulation techniques
(170.5280) Medical optics and biotechnology : Photon migration
(170.7050) Medical optics and biotechnology : Turbid media
Frédéric Bevilacqua, Andrew J. Berger, Albert E. Cerussi, Dorota Jakubowski, and Bruce J. Tromberg, "Broadband Absorption Spectroscopy in Turbid Media by Combined Frequency-Domain and Steady-State Methods," Appl. Opt. 39, 6498-6507 (2000)