Developmental changes of optical properties in neonates determined by near-infrared time-resolved spectroscopy

Near-infrared spectroscopy has been used for measurement of changes in cerebral Hb concentrations in infants to study cerebral oxygenation and hemodynamics. 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 (mu'(s)), cerebral Hb oxygen saturation (SCO2), cerebral blood volume (CBV), and differential pathlength factor (DPF), and the relationships between postconceptional age and mu'(s), SCO2, CBV, and DPF were investigated. A portable three-wavelength TRS system with a probe attached to the head of the neonate was used. The mean mu'(s) values at 761, 795, and 835 nm in neonates were estimated to be (mean +/- SD) 6.46 +/- 1.21, 5.90 +/- 1.15 and 6.40 +/- 1.16/cm, respectively. There was a significant positive relationship between postconceptional age and mu'(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 mu'(s), SCO2, CBV, and DPF in the neonatal brain at the bedside in an intensive care unit.