Investigating Developmental Changes in Scalp-Cortex Correspondence Using Diffuse Optical Tomography Sensitivity in Infancy

Abstract

Diffuse optical tomography (DOT) uses near-infrared light spectroscopy (NIRS) to measure changes in cerebral hemoglobin concentration. Anatomical interpretations of the location that generates the hemodynamic signal requires accurate descriptions of the cranio-cerebral relations and DOT sensitivity to the underlying cortical structures. Such information is limited for pediatric populations because they undergo rapid head and brain development. The present study used spatial scalp projection and photon propagation simulation methods to examine scalp-to-cortex distance, scalp-location-to-ROI mapping, and DOT sensitivity profiles in realistic head models based on MRIs. We investigated age-related differences in these measures among infants ranging from 2 weeks to 24 months with narrow age bins, children (4 and 12 years) and adults (20 to 24 years). There were age-group differences in the scalp-to-cortex distances in infancy. The developmental increase was magnified in children and adults. There were systematic age-related differences in the probabilistic mappings between scalp locations and cortical ROIs. The DOT sensitivity profiles displayed decreased fluence strength with increased penetration depth across groups. There were age-related differences in the DOT sensitivity profiles across a wide range of source-detector channel separations. Our findings have important implications in the design of sensor placement and DOT image reconstruction in NIRS and fNIRS research. Age-appropriate realistic head models should be used to provide anatomical guidance for standalone DOT data in infants.

Neural responses to happy, fearful and angry faces of varying identities in 5- and 7-month-old infants

“…Head probe geometry and cap placement photographs were used to virtually place the optodes on each MRI using previously developed methods ( Lloyd-Fox et al, 2014 ). Photon propagation modeling ( Fang, 2010 ) estimated diffuse optical tomography sensitivity functions from each source-detector pair comprising a channel ( Fu and Richards, 2020 ), confirmed with previously described geometrical methods ( Lloyd-Fox et al, 2014 ; Okamoto and Dan, 2005 ). Intersecting cortical regions were labeled using the LONI atlas ( Fillmore et al, 2015 ).…”

Age-related changes in diffuse optical tomography sensitivity profiles in infancy

“…The low scattering CSF may confine the S-D Channel DOT fluence distribution to shallower layers of the cortex especially at shorter source-detector separation distances. Fu and Richards (under review) [ 27 ] showed that the distance between the scalp channel location and the maximum fluence in the S-D Channel DOT fluence distribution was relatively shorter for the 2-week to 2-month groups. A direction for future research is to characterize morphological changes in specific tissue layers that are linked to age-related differences in S-D Channel DOT sensitivity profiles across separation distances.…”

“…The MRIs were obtained from open-access databases and a local scanning facility. Details of the sample are described in [ 27 ]. Table 1 presents the number of MRIs for the open access databases, separately for age and gender.…”

The neural correlates of inhibitory control in 10-month-old infants: a functional near-infrared spectroscopy study

“…Mapping of the channel locations to the AAL atlas (Shi et al, 2011) using the forward model allowed us to locate brain activation to specific areas of the PFC and parietal cortex (namely, the right inferior and superior parietal gyrus, the right middle frontal gyrus/right DLPFC and the right orbital middle gyrus/orbital PFC) with much more specificity than EEG, which is more commonly used to investigate the neural correlates of early executive function development (Bell & Fox, 1992;Cuevas et al, 2012;Whedon et al, 2020). Whilst the use of subject-specific head models would improve the accuracy of models of light transport (Cooper et al, 2012;Ferradal et al, 2014;Fu & Richards, 2020), this would require a MRI scan to be obtained from each participant. Given the difficulty and practical limitations of acquiring subject-specific MRI data from infants, this was not feasible in the current study.…”