Abstract
Near-infrared spectroscopy (NIRS) has become an increasingly valuable tool to monitor tissue oxygenation (T(oxy)) in vivo. Observations of changes in the absorption of light with T(oxy) have been recognized as early as 1876, leading to a milestone NIRS paper by Jöbsis in 1977. Changes in the absorption and scatting of light in the 700-850-nm range has been successfully used to evaluate T(oxy). The most practical devices use continuous-wave light providing relative values of T(oxy). Phase-modulated or pulsed light can monitor both absorption and scattering providing more accurate signals. NIRS provides excellent time resolution (~ 10 Hz), and multiple source-detector pairs can be used to provide low-resolution imaging. NIRS has been applied to a wide range of populations. Continued development of NIRS devices in terms of lower cost, better detection of both absorption and scattering, and smaller size will lead to a promising future for NIRS studies.