Introduction
During the perinatal period, the brain undergoes anatomical, functional, and metabolic changes. The anatomical changes include neuronal proliferation, migration, organization and myelination, and the metabolic changes match the process of initial overproduction and subsequent elimination of excessive neurons, synapses, and dendritic spines known to occur in the developing brain. Noninvasive assessment of cerebral anatomical changes and of oxygen delivery and utilization is useful for evaluating the effectiveness of therapy and for preventing oxygen toxicity in seriously ill neonates. Near-infrared spectroscopy (NIRS) has been used for measurement of changes in cerebral hemoglobin (Hb) concentrations in infants to study cerebral oxygenation and hemodynamics.
Methods
In this study, measurements by time-resolved spectroscopy (TRS) were performed in 22 neonates to estimate the values of light absorption coefficient and reduced scattering coefficient (μ's), cerebral Hb oxygen saturation (ScO2), cerebral blood volume (CBV), and differential pathlength factor (DPF), and the relationships between postconceptional age and μ's, ScO2, CBV, DPF were investigated. A portable three-wavelength TRS system (TRS-10, Hamamatsu Photonics K.K.) with a probe attached to head of the neonate was used.
Results and Discussions
The mean μ's values at 761, 795 and 835 nm in neonates were estimated to be 6.46 ± 1.21 (mean ± SD), 5.90 ± 1.15 and 6.40 ± 1.16 /cm, respectively. There was a significant positive relationship between postconceptional age and μ's at those three wavelengths. The mean ScO2 value was calculated to be 70.0 ± 4.6%, and postconceptional age and ScO2 showed a negative linear relationship. The mean value of CBV was 2.31 ± 0.56 ml/100 g. There was a significant positive relationship between postconceptional age and CBV. The mean DPF values at 761, 795 and 835 nm were estimated to be 4.58 ± 0.41, 4.64 ± 0.46 and 4.31 ± 0.42, respectively. There was no relationship between postconceptional age and DPF at those three wavelengths. The results demonstrated that our near-infrared TRS method can be used to monitor μ's, ScO2, CBV and DPF in the neonatal brain at the bedside in an intensive care unit.