ABSTRACT
The basis for most noninvasive optical measurements of brain function is the wavelength dependent absorption spectrum of the oxygenated and deoxygenated forms of hemoglobin. Noninvasive imaging with near infrared (NIR) light holds great promise for imaging in the brain in both animals and humans. The spatial resolution of NIR images is typically significantly lower than that of magnetic resonance imaging but NIR imaging provides unique physiological information because of its sensitivity to oxy- and deoxy hemoglobin as well as exogenous fluorophores. NIR measurement configurations can be classified into three categories: time-domain, frequency-domain and continuous wave. Useful information can be extracted from NIR measurements due to the unique spectral absorption characteristics of biological chromophores as well as to exogenous contrast agents. NIR spectroscopy measurements typically do not involve full image reconstruction and therefore, consist primarily of spatially integrated time courses of hemoglobin oxygenation and volume changes.
