Cerebral baseline optical and hemodynamic properties in pediatric population: a large cohort time-domain near-infrared spectroscopy study.

Significance: Reference cerebral near-infrared spectroscopy (NIRS) data on the pediatric population are scarce, and in most cases, only cerebral oxygen saturation ( ${\mathrm{SO}}_2$ ) measured by continuous wave spatially resolved spectroscopy NIRS is reported. Absolute data for baseline optical and hemodynamic parameters are missing.

Aim: We aimed at collecting baseline cerebral optical parameters [absorption coefficient, ${\mu }_a$ ; reduced scattering coefficient, ${\mu }_s^{\text{'}}$ ; differential pathlength factor (DPF)] and hemodynamic parameters [oxy-hemoglobin content ( ${\mathrm{HbO}}_2$ ), deoxyhemoglobin content (HHb), total hemoglobin content (tHB), ${\mathrm{SO}}_2$ ] in a large cohort of pediatric patients. The objectives are to establish reference optical values in this population and evaluate the reproducibility of a commercial time domain (TD) NIRS tissue oximeter.

Approach: TD NIRS measurements were performed in the prefrontal cortex at 686 and 830 nm with a 2.5-cm source-detector distance and 1-Hz acquisition rate. Five independent measurements (after probe replacement) were taken for every subject. TD NIRS data were fitted to a photon diffusion model to estimate the optical parameters. From the absorption coefficients, the hemodynamic parameters were derived by Beer's law. Auxological and physiological information was also collected to explore the potential correlations with NIRS data.

Results: We measured 305 patients in the age range of 2 to 18 years. Absolute values for baseline optical and hemodynamic parameters were shown as a function of age and auxological variables. From the analysis of the repositioning after probe replacement, the time-domain near-infrared spectroscopy device exhibited an average precision (intended as coefficient of variation) of $<5\%$ for ${\mu }_s^{\text{'}}$ , DPF, ${\mathrm{HbO}}_2$ , HHb, and tHb, whereas precision was $<2\%$ for ${\mathrm{SO}}_2$ .

Conclusions: We provided baseline values for optical and hemodynamic parameters in a large cohort of healthy pediatric subjects with good precision, providing a foundation for future investigations into clinically relevant deviations in these parameters.