Abstract
.In diffuse optical tomography (DOT), overlapping and multidistance measurements are required to reconstruct depth-resolved images of oxy- () and deoxy- (HHb) hemoglobin concentration changes occurring in the brain. These can be considered an indirect measure of brain activity, under the assumption of intact neurovascular coupling. Broadband systems also allow changes in the redox state of cytochrome c oxidase (oxCCO) to be measured, which can be an important biomarker when neurovascular coupling is impaired. We used DOT to reconstruct images of , , and from data acquired with a broadband system. Four healthy volunteers were measured while performing a visual stimulation task (4-Hz inverting checkerboard). The broadband system was configured to allow multidistance and overlapping measurements of the participants’ visual cortex with 32 channels. A multispectral approach was employed to reconstruct changes in concentration of the three chromophores during the visual stimulation. A clear and focused activation was reconstructed in the left occipital cortex of all participants. The difference between the residuals of the three-chromophore model and of the two-chromophore model (recovering only and ) exhibits a spectrum similar to that of oxCCO. These results form a basis for further studies aimed to further optimize image reconstruction of .
Highlights
Near-infrared spectroscopy (NIRS) uses light in the red and near-infrared range to monitor concentration changes of oxy(HbO2) and deoxy- (HHb) hemoglobin in the brain.[1]
*Address all correspondence to: Sabrina Brigadoi, E-mail: sabrina.brigadoi@ unipd.it functional magnetic resonance imaging (fMRI). Both functional NIRS and fMRI rely on the assumption of intact neurovascular coupling, this assumption is frequently violated in cases of brain pathology.[8,9,10,11]
There is some variability in the residuals among participants likely due to: (1) each participant can have a different timing of brain activation and (2) the retinotopic mapping of the visual cortex is different in each person, increasing the chance that each channel is probing slightly different brain visual areas in each participant.[46]
Summary
Near-infrared spectroscopy (NIRS) uses light in the red and near-infrared range to monitor concentration changes of oxy(HbO2) and deoxy- (HHb) hemoglobin in the brain.[1]. They can be employed to monitor vulnerable subjects, such as neonates,[4,5,6] patients with implanted devices,[2] or critically ill patients who need bedside monitoring[7] and who could not be previously monitored with fMRI Both functional NIRS (fNIRS) and fMRI rely on the assumption of intact neurovascular coupling, this assumption is frequently violated in cases of brain pathology.[8,9,10,11] Pathology (e.g., acute brain injury, cerebral ischemia, and neurodegenerative disease) can alter the regional hemodynamic response to localized changes in metabolism and in extreme cases can lead to absence or inversion of the response. There is an unmet clinical need for a direct marker of cerebral metabolism
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