Novel NIR instrument for non-invasive monitoring and quantification of cerebral tissue blood supply and oxygenation

We report the use of a pseudo-random modulated (PRM), low power laser diode based and dual wavelength NIR instrument for non-invasive, time-resolved spectroscopy (TRS) monitoring and quantification of the cerebral tissue blood supply and oxygenation. In vivo experiment have been conducted with dogs under hypoxia, hypercarbia and hemodilution conditions. Cerebral tissue blood supply and oxygenation are monitored through TRS of photon migration at wavelengths of 670nm and 810nm respectively. By chi(2) curve fitting the measured TRS with effective scattering and absorption coefficients as two variables, both effective scattering and absorption coefficients at each wavelength are extracted. It is found that under hypoxia condition, both scattering and absorption coefficients increases with the hypoxic level. This agrees with the physiology that the blood supply increases while the blood oxygenation decreases under hypoxia. Under hypercarbia condition, both scattering and absorption coefficients of 670nm decreases with the increase of the hypercarbia level whereas those of 810nm increases. These correspond to the increased blood supply and oxygenation. Under hemodilution condition, both scattering and absorption coefficients at both wavelengths decreases when the anemia level increases. Therefore, the cerebral tissue blood supply and oxygenation can be monitored and quantified in real-time and non-invasive manner.