Near-Infrared Fluorescence Imaging and Spectroscopy in Random Media and Tissues
Most radiation-based spectroscopic and imaging techniques typically depend on evaluation of a nonscattered or singly scattered signal for retrieval of quantitative information. For example, absorption spectroscopy depends on the survival of unscattered light across a known pathlength,
; dynamic-light scattering or photon-correlation spectroscopy, because of its scatter by Brownian motion out of the optical path, requires the fluctuation of light intensity; x-ray and computed x-ray tomography depend on the straight-line path of nonabsorbed x-rays; and so forth. Yet most systems of interest multiply scatter radiation of low energy and require diluted suspensions or nonscattering media when dealing with optical interrogation. Hence, optical techniques developed for imaging and spectroscopy are usually plagued by scatter influence. To expand the quantitative applicability of optical techniques to these real systems new techniques have been developed that focus on coherence properties, temporal and spatial correlation, and other properties; these allow for the extraction of nonscattered or singly scattered light from a multiply scattered signal. Yet these approaches neglect the scattered signal, which is the largest portion of the signal, in favor of that portion that possesses the smallest signal-to-noise ratio (SNR).