Broadband absorption spectroscopy by combining frequency-domain and steady-state techniques

A technique for measuring broadband near-infrared absoprtion spectra of turbid media is presented using a combination of frequency-domain (FD) and steady-state (SS) reflectance methods. Most of the wavelength coverage is provided by a white-light SS measurement, while the FD data are acquired at a few selected wavelengths. Coefficients of absorption (μa) and reduced scattering (μs') derived from the FD data are used to intensity-calibrate the SS measurements and to estimate μs'at all wavelengths in the spectral window of interest. After these steps are performed, μa can be determined by comparing the SS reflectance values to the predictions of diffusion theory, wavelength by wavelength. We present an application of this method to breast tumor characterization. A case study of a fibroadenoma is shown, where different absorption spectra were found between the normal and the tumor sides