A technique for measuring broadband near-infrared absorption spectra of
turbid media that uses a combination of frequency-domain and steady-state
reflectance methods. Most of the wavelength coverage is provided by a
white-light steady-state measurement, whereas the frequency-domain data
are acquired at a few selected wavelengths. Coefficients of absorption
and reduced scattering derived from the frequency-domain data are used to
calibrate the intensity of the steady-state measurements and to determine
the reduced scattering coefficient at all wavelengths in the spectral
window of interest. The absorption coefficient spectrum is determined by
comparing the steady-state reflectance values with the predictions of
diffusion theory, wavelength by wavelength. Absorption spectra of a
turbid phantom and of human breast tissue in vivo, derived with the
combined frequency-domain and steady-state technique, agree well with
expected reference values.