| Near infrared spectroscopy (NIBS) has been used for determination of tissue optical properties. This technique has been especially useful for in vivo monitoring of hemodynamics and oxygen saturation in tissue. For this work, I have developed a large-ranged multidistance probe for NIBS, which allows measurements of cerebral hemodynamics and oxygen saturation. The measurements on the adult forehead were analyzed using a two-layer model of the adult head. The average values of the hemodynamic parameters and their fluctuations were determined for a group of 30 subjects. In addition to base line, we also investigated cerebral vasomotion which results in spontaneous oscillation of the hemoglobin content in the brain. The spatio-temporal structural of the cerebral vasomotion was investigated by use of phase portrait, cross-correlation, and nonlinear dynamics analytical methods. We found that the cerebral vasomotion is temporally coherent as well as spatially coherent. The correlation lengths for temporal and spatial coherence are about 3min and 1--2 cm in our measurements. Cerebral vasomotion couples to brain activity by changing the phase of the oxy and deoxy-hemoglobin concentration waves to be in phase with a periodic task. |
