Enhancing diffuse correlation spectroscopy pulsatile cerebral blood flow signal with near-infrared spectroscopy photoplethysmography

SIGNIFICANCE: Combining near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) allows for quantifying cerebral blood volume, flow, and oxygenation changes continuously and non-invasively. As recently shown, the DCS pulsatile cerebral blood flow index ([Formula: see text]) can be used to quantify critical closing pressure (CrCP) and cerebrovascular resistance ([Formula: see text]). AIM: Although current DCS technology allows for reliable monitoring of the slow hemodynamic changes, resolving pulsatile blood flow at large source–detector separations, which is needed to ensure cerebral sensitivity, is challenging because of its low signal-to-noise ratio (SNR). Cardiac-gated averaging of several arterial pulse cycles is required to obtain a meaningful waveform. APPROACH: Taking advantage of the high SNR of NIRS, we demonstrate a method that uses the NIRS photoplethysmography (NIRS-PPG) pulsatile signal to model DCS [Formula: see text] , reducing the coefficient of variation of the recovered pulsatile waveform ([Formula: see text]) and allowing for an unprecedented temporal resolution (266 Hz) at a large source-detector separation ([Formula: see text]). RESULTS: In 10 healthy subjects, we verified the quality of the NIRS-PPG [Formula: see text] during common tasks, showing high fidelity against [Formula: see text] ([Formula: see text] [Formula: see text]). We recovered CrCP and [Formula: see text] at 0.25 Hz, [Formula: see text] times faster than previously achieved with DCS. CONCLUSIONS: NIRS-PPG improves DCS [Formula: see text] SNR, reducing the number of gate-averaged heartbeats required to recover CrCP and [Formula: see text].