Abstract
Blood oxygenation level dependent (BOLD)–based functional MRI (fMRI) is a widely utilized neuroimaging technique for mapping brain function. Hematocrit (HCT), a global hematologic marker of the amount of hemoglobin in blood, is known to impact task-evoked BOLD activation. Yet, its impact on resting-state fMRI (R-fMRI) measures has not been characterized. We address this gap by testing for associations between HCT level and inter-individual variation in commonly employed R-fMRI indices of intrinsic brain function from 45 healthy adults. Given known sex differences in HCT, we also examined potential sex differences. Variation in baseline HCT among individuals were associated with regional differences in four of the six intrinsic brain indices examined. Portions of the default (anterior cingulate cortex/medial prefrontal cortex: ACC/MPFC), dorsal attention (intraparietal sulcus), and salience (insular and opercular cortex) network showed relationships with HCT for two measures. The relationships within MPFC, as well as visual and cerebellar networks, were modulated by sex. These results suggest that inter-individual variations in HCT can serve as a source of variations in R-fMRI derivatives at a regional level. Future work is needed to delineate whether this association is attributable to neural or non-neuronal source of variations and whether these effects are related to acute or chronic differences in HCT level.
Highlights
Blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging is one of the most widely utilized non-invasive imaging techniques that indirectly measure brain functions
The BOLD signal indexes the total amount of deoxygenated hemoglobin present in a given brain area, which is taken to reflect the balance between oxygen consumption and oxygen supply (Huettel et al, 2009)
While each RfMRI measure revealed a distinct set of associations, overlaps were observed within anterior cingulate cortex/medial prefrontal cortex (ACC/MPFC: in DC and DR_Lateral visual), intraparietal sulcus (IPS: in VMHC and DR_Occipital pole), and insular/central opercular cortex, suggesting that the intrinsic features of these areas may be vulnerable to the impact of HCT
Summary
Blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) is one of the most widely utilized non-invasive imaging techniques that indirectly measure brain functions. BOLD-fMRI relies on the magnetic properties of hemoglobin (Hb)—the metalloprotein in red blood cells that transport oxygen (Ogawa et al, 1990a,b, 1992). The BOLD signal indexes the total amount of deoxygenated hemoglobin (deoxy-Hb) present in a given brain area, which is taken to reflect the balance between oxygen consumption and oxygen supply (Huettel et al, 2009). The extent to which the BOLD signal changes in response to this process is dependent on the concentration of Hb in the blood, which is commonly represented by hematocrit (HCT; the percentage of red blood cells in the whole blood volume) (Levin et al, 2001; Gustard et al, 2003). It may be of value to consider the potential influences of HCT on BOLD fMRI measures
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