Near-infrared spectroscopy (NIRS) is a noninvasive medical technology that uses visible red and near-infrared light to probe changes in the concentrations of absorbers in tissue. In functional NIRS (fNIRS), local hemoglobin concentration changes in brain are measured, which can be interpreted as changes in cerebral blood flow and volume, and are related to neuronal activation. NIRS is an especially suitable imaging modality for neonates as the instrumentation is safe, portable and silent compared to, e.g., positron emission tomography and functional magnetic resonance imaging. Also, neonates are especially suitable subjects for fNIRS because of their small head size, thin scalp and skull and undeveloped myelination. In this Thesis, instrumentation and software for an optical tomography system were developed to improve the usability and data quality to allow fNIRS imaging of brain function in neonates and young infants. Also, measurement and data analysis methods were developed. The usability of the improvements was demonstrated by performing measurements of auditory evoked hemodynamic responses in neonates. Neuroscientific aims included the study of newborn brain function, the properties of hemodynamic responses and lateralization of speech and music processing. The results of the Thesis show that neonatal brain studies with NIRS are feasible; NIRS can measure hemodynamic responses to stimulation and is well accepted by neonates. Hemodynamic responses to auditory stimuli were found to be changing rapidly around the time of birth and they correlate with sleep stage. The hemodynamic response to speech was found to be located on the left hemisphere already at the time of birth. This may be taken as an evidence that leftward lateralization of speech is already established at birth at least to some extent. The results also showed a large amount of inter-individual variations in hemodynamic responses in newborns. This is probably in part due to anatomical differences between individuals. A robust optical reconstruction method based on a realistic anatomical model of optical properties at the actual measurement area and a high-density measurement array is likely to reduce the variability and portray true responses more accurately. Monitoring of sleep stage, global systemic responses, and spontaneous hemodynamic oscillations should also be beneficial.
|Publication status||Published - 2015|
|MoE publication type||G5 Doctoral dissertation (article)|
- near-infrared spectroscopy, NIRS, newborns, brain research, lateralization of brain function, auditory stimulus, hemodynamic response