Differential absorption imaging with optical coherence tomography

The spatial variation of the backscattering cross section is the primary source of contrast in present applications of optical coherence tomography (OCT). We introduce and analyze a technique for obtaining OCT images of the local concentration of an absorbing compound in biological tissues and other highly scattering media. A pair of light-emitting diodes, one emitting in a vibrational absorption band of the chemical compound of interest and the other emitting just outside this band, are used as sources at the input of the interferometer. The differential absorption of the probe beam is determined by Fourier transformation and ratiometric processing of the measured interference signals. The ability of the technique to distinguish lipid and water inclusions in a scattering material is demonstrated with an OCT system that uses a pair of light-emitting-diode sources with center wavelengths of 1.3 mu m and 1.46 mu m. (C) 1998 Optical Society of America.