Axial variation of deoxyhemoglobin density as a source of the low-frequency time lag structure in blood oxygenation level-dependent signals

Abstract

Perfusion-related information is reportedly embedded in the low-frequency component of a blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signal. The blood-propagation pattern through the cerebral vascular tree is detected as an interregional lag variation of spontaneous low-frequency oscillations (sLFOs). Mapping of this lag, or phase, has been implicitly treated as a projection of the vascular tree structure onto real space. While accumulating evidence supports the biological significance of this signal component, the physiological basis of the “perfusion lag structure,” a requirement for an integrative resting-state fMRI-signal model, is lacking. In this study, we conducted analyses furthering the hypothesis that the sLFO is not only largely of systemic origin, but also essentially intrinsic to blood, and hence behaves as a virtual tracer. By summing the small fluctuations of instantaneous phase differences between adjacent vascular regions, a velocity response to respiratory challenges was detected. Regarding the relationship to neurovascular coupling, the removal of the whole lag structure, which can be considered as an optimized global-signal regression, resulted in a reduction of inter-individual variance while preserving the fMRI response. Examination of the T2* and S0, or non-BOLD, components of the fMRI signal revealed that the lag structure is deoxyhemoglobin dependent, while paradoxically presenting a signal-magnitude reduction in the venous side of the cerebral vasculature. These findings provide insight into the origin of BOLD sLFOs, suggesting that they are highly intrinsic to the circulating blood.

The relationship between attention and avoidance coping in anorexia nervosa: functional magnetic resonance imaging study

“…Finally, a recently proposed denoising method 27,28 was used to cope with contamination from non-neural signal components. This procedure involves tracking regional variations of low-frequency oscillations of systemic origin, using the bandpass-filtered (0.008–0.07 Hz) global signal as an initial seed.…”

An MRI protocol for anatomical and functional evaluation of the California sea lion brain

“…Many regions, notably arteries in the inferior slices, fluctuated at the pseudo-periodic rate of the manual ventilation and exhibited high signal variance, strongly suggesting a BOLD signal change due either to non-stationary arterial CO 2 (Tong & Frederick 2010, Tong et al . 2019) and/or non-stationary deoxyhemoglobin concentration in arterial blood whenever SaO 2 departs from the assumed value of 100% (Aso et al 2019). Such respiration-induced changes are typical in humans.…”

The Role of Cerebrovascular-Reactivity Mapping in Functional MRI: Calibrated fMRI and Resting-State fMRI

“…It is further shown that by accounting for the temporal shifts in the BOLD CO2 response, improved CVR estimates can be obtained ( Yao et al, 2021 ). Furthermore, this CO 2 -related shift structure can be associated with the lag structure that naturally occurs in the rs-fMRI signal ( Tong and Frederick, 2014 ; Aso et al, 2019 ), and can be capitalized to extract additional vascular information without CO 2 challenges.…”