Near infrared spectroscopy is a powerful technique to evaluate hemodynamics in cerebral tissue where the light used is subject to the low scattering effect. In this wavelength range, hemoglobin has the characteristic absorption spectra. Because of the noninvasive method, this gives valuable information containing venous blood to the clinical field such as cardiac surgery, neurosurgery and pediatrics. Although the technique originates from classical biochemistry with clear solution, researchers have proposed creative ideas to be suitable for measuring hemodynamics in living tissue optically. In this mini-review, theoretical basis from Lambert-Beer law to multiwavelength method and derivation of the linear relationship between absorption and concentration of pigments from the time-resolved method are described. Furthermore the recent advances are also outlined.

ear infrared spectroscopy, hemoglobin, absorption, concentration, Lambert-Beer law, time resolved spectroscopy