Person:

Franceschini, Maria

The near infrared spectroscopy (NIRS) frequency-domain multi-distance (FD-MD) method allows for the estimation of optical properties in biological tissue using the phase and intensity of radiofrequency modulated light at different source-detector separations. In this study, we evaluated the accuracy of this method to retrieve the absorption coefficient of the brain at different ages. Synthetic measurements were generated with Monte Carlo simulations in magnetic resonance imaging (MRI)-based heterogeneous head models for four ages: newborn, 6 and 12 month old infants, and adult. For each age, we determined the optimal set of source-detector separations and estimated the corresponding errors. Errors arise from different origins: methodological (FD-MD) and anatomical (curvature, head size and contamination by extra-cerebral tissues). We found that the brain optical absorption could be retrieved with an error between 8-24% in neonates and infants, while the error increased to 19-44% in adults over all source-detector distances. The dominant contribution to the error was found to be the head curvature in neonates and infants, and the extra-cerebral tissues in adults.

Little is known about cerebral blood flow, cerebral blood volume (CBV), oxygenation, and oxygen consumption in the premature newborn brain. We combined quantitative frequency-domain near-infrared spectroscopy measures of cerebral hemoglobin oxygenation ((SO_2)) and CBV with diffusion correlation spectroscopy measures of cerebral blood flow index ((BF_{ix})) to determine the relationship between these measures, gestational age at birth (GA), and chronological age. We followed 56 neonates of various GA once a week during their hospital stay. We provide absolute values of (SO_2) and CBV, relative values of (BF_{ix}), and relative cerebral metabolic rate of oxygen ((rCMRO_2)) as a function of postmenstrual age (PMA) and chronological age for four GA groups. (SO_2) correlates with chronological age (r=−0.54, P value (\leq)0.001) but not with PMA (r=−0.07), whereas (BF_{ix}) and (rCMRO_2) correlate better with PMA (r=0.37 and 0.43, respectively, P value (\leq)0.001). Relative (CMRO_2) during the first month of life is lower when GA is lower. Blood flow index and (rCMRO_2) are more accurate biomarkers of the brain development than (SO_2) in the premature newborns.