QUANTITATIVE OPTICAL SPECTROSCOPY FOR TISSUE DIAGNOSIS

The interaction of light within tissue has been used to recognize dise ase since the mid-1800s. The recent developments of small light source s, detectors, and fiber optic probes provide opportunities to quantita tively measure these interactions, which yield information for diagnos is at the biochemical, structural, or (patho)physiological level withi n intact tissues. However, because of the strong scattering properties of tissues, the reemitted optical signal is often influenced by chang es in biochemistry (as detected by these spectroscopic approaches) and by physiological and pathophysiological changes in tissue scattering. One challenge of biomedical optics is to uncouple the signals influen ced by biochemistry, which themselves provide specificity for identify ing diseased states, from those influenced by tissue scattering, which are typically unspecific to a pathology. In this review, we describe optical interactions pursued for biomedical applications (fluorescence , fluorescence lifetime, phosphorescence, and Raman from cells, cultur es, and tissues) and then provide a descriptive framework for light in teraction based upon tissue absorption and scattering properties. Fina lly, we review important endogenous and exogenous biological chromopho res and describe current work to employ these signals for detection an d diagnosis of disease.