Characterizing dynamic cerebral vascular reactivity using a hybrid system combining time-resolved near-infrared and diffuse correlation spectroscopy

Abstract

This study presents the characterization of dynamic cerebrovascular reactivity (CVR) in healthy adults by a hybrid optical system combining time-resolved (TR) near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS). Blood flow and oxygenation (oxy- and deoxy-hemoglobin) responses to a step hypercapnic challenge were recorded to characterize dynamic and static components of CVR. Data were acquired at short and long source-detector separations (rSD) to assess the impact of scalp hemodynamics, and moment analysis applied to the TR-NIRS to further enhance the sensitivity to the brain. Comparing blood flow and oxygenation responses acquired at short and long rSD demonstrated that scalp contamination distorted the CVR time courses, particularly for oxyhemoglobin. This effect was significantly diminished by the greater depth sensitivity of TR NIRS and less evident in the DCS data due to the higher blood flow in the brain compared to the scalp. The reactivity speed was similar for blood flow and oxygenation in the healthy brain. Given the ease-of-use, portability, and non-invasiveness of this hybrid approach, it is well suited to investigate if the temporal relationship between CBF and oxygenation is altered by factors such as age and cerebrovascular disease.

Direct assessment of extracerebral signal contamination on optical measurements of cerebral blood flow, oxygenation, and metabolism

“…This finding is in agreement with the results of our previous study that applied moment analysis to functional NIRS data. 61 The greater sensitivity of deoxyhemoglobin to cerebral hemodynamics also agrees with a previous study by Kirilina et al 65 The temporal fluctuations in the time courses presented in Figs. 4 and 5 illustrate that the SNR decreased as the order of the statistical moment increased, which is expected, given the fewer number of late-arriving photons detected.…”

“…This finding is in agreement with the results of our previous study that applied moment analysis to functional NIRS data. 61 The greater sensitivity of deoxyhemoglobin to cerebral hemodynamics also agrees with a previous study by Kirilina et al. 65 …”

“… 73 , 74 Changes in heart rate and blood pressure caused by the hypercapnic challenge could also lead to changes in blood flow and oxygenation in peripheral tissues. In a recent publication, 61 significant increases in both parameters were caused by a increase of 15 mmHg. Consider the inherent sensitivity of these optical techniques to superficial tissue, hemodynamic responses in scalp tissue would not have to be as large as cerebrovascular responses to cause significant signal changes.…”

“…The changes in scalp hemodynamics likely resulted from hypercapnia-induced increases in heart rate and blood pressure. 61 These indicate that a latent vasodilatory response to hypercapnia in the scalp considering functional magnetic resonance imaging studies have shown rapid cerebrovascular reactivity in the healthy brain. 62 – 64 Across all three moments, the ECL contribution was consistently smaller for compared with , indicating that the former was less sensitive to scalp hemodynamics.…”

Perfusion and Metabolic Neuromonitoring during Ventricular Taps in Infants with Post-Hemorrhagic Ventricular Dilatation

“…Alternately, truly simultaneous measurements could be achieved using optical filters to selectively block B-NIRS and DCS light sources from the opposing detectors. Recent works describing hybrid B-NIRS/DCS and time-resolved NIRS/DCS systems utilizing bandpass and notch filters have been proposed [50,52,53].…”