Vascular origins of low‐frequency oscillations in the cerebrospinal fluid signal in resting‐state fMRI: Interpretation using photoplethysmography. Issue 8 (27th February 2021)

• Record Type: Journal Article
• Authors: Attarpour, Ahmadreza; Ward, James; Chen, J. Jean
• Is Part Of: Human brain mapping. Volume 42:Issue 8(2021)
• Page Start: 2606
• Page End: 2622
• Publication Date: 2021-02-27
• Subjects: arterial BOLD -- cerebrospinal fluid -- functional connectivity -- heart‐rate variability -- Mayer wave -- photoplethysmograph -- pulse‐intensity ratio -- resting‐state fMRI -- second derivative of PPG -- vasomotion -- venous BOLD; Brain mapping -- Periodicals; 611.81
• DOI: 10.1002/hbm.25392
• Languages: English
• ISSNs: 1065-9471

Abstract

Abstract: In vivo mapping of cerebrovascular oscillations in the 0.05–0.15 Hz remains difficult. Oscillations in the cerebrospinal fluid (CSF) represent a possible avenue for noninvasively tracking these oscillations using resting‐state functional MRI (rs‐fMRI), and have been used to correct for vascular oscillations in rs‐fMRI functional connectivity. However, the relationship between low‐frequency CSF and vascular oscillations remains unclear. In this study, we investigate this relationship using fast simultaneous rs‐fMRI and photoplethysmogram (PPG), examining the 0.1 Hz PPG signal, heart‐rate variability (HRV), pulse‐intensity ratio (PIR), and the second derivative of the PPG (SDPPG). The main findings of this study are: (a) signals in different CSF regions are not equivalent in their associations with vascular and tissue rs‐fMRI signals; (b) the PPG signal is maximally coherent with the arterial and CSF signals at the cardiac frequency, but coherent with brain tissue at ~0.2 Hz; (c) PIR is maximally coherent with the CSF signal near 0.03 Hz; and (d) PPG‐related vascular oscillations only contribute to ~15% of the CSF (and arterial) signal in rs‐fMRI. These findings caution against averaging all CSF regions when extracting physiological nuisance regressors in rs‐fMRI applications, and indicate the drivers of the CSF signal are more than simply cardiac. Our study is an initial attempt at the refinement and standardization of how the CSF signal in rs‐fMRI can be used and interpreted. It also paves the way for using rs‐fMRI in the CSF as a potential tool for tracking cerebrovascular health through, for instance, the potential relationship between PIR and the CSF signal. Abstract : The characterization of the CSF signal in rs‐fMRI is useful for denoising the rs‐fMRI signal, for understanding the appropriate measurement of CSF fluctuations using fMRI and also for determining what aspects of vascular health may be reflected by measuring CSF fluctuations. In this work, we show that the CSF signals measured from various brain regions are not equivalent, and demonstrate the manner in which each CSF region is affected by the pulse. This information can pave the way for the refinement and standardization of how the CSF signal in rs‐fMRI can be used.