Vascular origins of low-frequency oscillations in cerebrospinal fluid resting-state fMRI signal: Interpretation using photoplethysmography

Due to its cardiogenic constituents, the cerebrospinal fluid (CSF) contribution to resting-state functional MRI (rs-fMRI) has been used for denoising. Recently, it has become increasingly used for characterizing CSF flow and glymphatic flow. However, the association between CSF and vascular oscillations in rs-fMRI remains to be fully understood. In this study, we quantify the relationship between rs-fMRI fluctuation in different CSF compartments and photoplethysmography (PPG) recordings, focusing on the frequency band around 0.1 Hz. We also quantify their relationship between the rs-fMRI signals (in CSF, tissue and vasculature) and other vascular measures derived from PPG traces.