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

Abstract

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 (pCBF i) can be used to quantify critical closing pressure (CrCP) and cerebrovascular resistance (CVR i). 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 pCBF i , reducing the coefficient of variation of the recovered pulsatile waveform (pCBF i-fit) and allowing for an unprecedented temporal resolution (266 Hz) at a large source-detector separation (>3 cm). Results: In 10 healthy subjects, we verified the quality of the NIRS-PPG pCBF i-fit during common tasks, showing high fidelity against pCBF i (R 2 0.98 AE 0.01). We recovered CrCP and CVR i at 0.25 Hz, >10 times faster than previously achieved with DCS. Conclusions: NIRS-PPG improves DCS pCBF i SNR, reducing the number of gate-averaged heartbeats required to recover CrCP and CVR i .