Shedding light on the neonatal brain: probing cerebral hemodynamics by diffuse optical spectroscopic methods

Abstract

Investigating the cerebral physiology of healthy term newborns' brains is important for better understanding perinatal brain injuries, of which the most common etiologies are hypoxia and ischemia. Hence, cerebral blood flow and cerebral oxygenation are important biomarkers of brain health. In this study, we employed a hybrid diffuse optical system consisting of diffuse correlation spectroscopy (DCS) and frequency-domain near infrared spectroscopy (FDNIRS) to measure hemoglobin concentration, oxygen saturation, and indices of cerebral blood flow and metabolism. We measured 30 term infants to assess the optical and physiological characteristics of the healthy neonatal brain in the frontal, temporal, and parietal lobes. We observed higher metabolism in the right hemisphere compared to the left and a positive correlation between gestational age and the level of cerebral hemoglobin concentration, blood volume, and oxygen saturation. Moreover, we observed higher cerebral blood flow and lower oxygen saturation in females compared to males. The delayed maturation in males and the sexual dimorphism in cerebral hemodynamics may explain why males are more vulnerable to perinatal brain injuries than females.

Figure 1

The measured absorption coefficient (μ_a) and reduced scattering coefficient $({\mu }_s\mathrm{\prime })$ of healthy newborns’ brains and their fitted spectrum. The green error bars indicate the mean and 95% confidence interval over all babies and locations. The dashed green line is the mean of fitted spectrum and the gray shaded area indicates the 95% confidence interval of the mean.

Figure 2

The distribution of the measured hemodynamic parameters and the mean standard deviation of the distribution. Histogram of [A] total hemoglobin concentration (HbT), [B] oxygen saturation (SO₂), and [C] cerebral blood flow index (CBF_i).

Figure 3

The sexual differences in cerebral hemodynamics represented with bar graphs, reporting the mean values and standard errors across infants. The green bars indicate males; yellow bars, females; and the red stars indicate the locations where there is statistically significant difference between males and females. The x-axis shows the site of measurement: the average over all locations, frontal, temporal, and parietal lobes. [A] Total hemoglobin concentration (HbT). [B] Oxygen saturation (SO₂). [C] Cerebral blood flow index (CBF_i). [D] Cerebral oxygen metabolism index (CMRO_2i).

Figure 4

The correlation between gestational age and [A] SO₂, [B] HbT. The dotted lines show the best linear fits.

Figure 5

[Left] The probe is gently located on the infant’s head while the infant is resting in the mother’s embrace. [Right] Schematic of the hybrid probe: FDNIRS (orange circles) consists of two sources and two detectors arranged in a way that provides four source-detector separations from 1.5 to 3 cm in steps of half a centimeter. DCS (blue circles) consists of one source and four detectors, all located at a distance of 2 cm from the source.

Figure 6

An example of fitting quality of the measured parameters. [A] The values of ln(AC.ρ²) as a function of source-detector distances (ρ) are presented by circles. Different colors correspond to different wavelengths (color-mapped in the legend) and the dashed lines are the corresponding linear fit. [B] Phase shift (radian) as a function of distance at the 8 wavelengths. [C] The circles are the measured absorption coefficients (μ_a) at 8 wavelengths; the blue line is the fitted absorption spectra of oxy- and deoxy-hemoglobin. [D] The circles are the reduced scattering coefficients (${\mu }_s\mathrm{\prime }$) at the 8 wavelengths and the blue line is the fitted scattering model. [E] The measured intensity autocorrelation function (red) measured with DCS and the fitted theoretical model (blue).