Noninvasive measurement of cerebral blood flow and blood oxygenation using near-infrared and diffuse correlation spectroscopies in critically brain-injured adults

Abstract

Background: This study assesses the utility of a hybrid optical instrument for noninvasive transcranial monitoring in the neurointensive care unit. The instrument is based on diffuse correlation spectroscopy (DCS) for measurement of cerebral blood flow (CBF), and near-infrared spectroscopy (NIRS) for measurement of oxy- and deoxy-hemoglobin concentration. DCS/NIRS measurements of CBF and oxygenation from frontal lobes are compared with concurrent xenon-enhanced computed tomography (XeCT) in patients during induced blood pressure changes and carbon dioxide arterial partial pressure variation.

Methods: Seven neurocritical care patients were included in the study. Relative CBF measured by DCS (rCBF(DCS)), and changes in oxy-hemoglobin (DeltaHbO(2)), deoxy-hemoglobin (DeltaHb), and total hemoglobin concentration (DeltaTHC), measured by NIRS, were continuously monitored throughout XeCT during a baseline scan and a scan after intervention. CBF from XeCT regions-of-interest (ROIs) under the optical probes were used to calculate relative XeCT CBF (rCBF(XeCT)) and were then compared to rCBF(DCS). Spearman's rank coefficients were employed to test for associations between rCBF(DCS) and rCBF(XeCT), as well as between rCBF from both modalities and NIRS parameters.

Results: rCBF(DCS) and rCBF(XeCT) showed good correlation (r (s) = 0.73, P = 0.010) across the patient cohort. Moderate correlations between rCBF(DCS) and DeltaHbO(2)/DeltaTHC were also observed. Both NIRS and DCS distinguished the effects of xenon inhalation on CBF, which varied among the patients.

Conclusions: DCS measurements of CBF and NIRS measurements of tissue blood oxygenation were successfully obtained in neurocritical care patients. The potential for DCS to provide continuous, noninvasive bedside monitoring for the purpose of CBF management and individualized care is demonstrated.

Figures

Fig. 1

Right: Schematic of the source–detector separation of the optical probe. The resulting area of highest probability signal origin is shown as dark gray, with the lighter areas having lower probability of signal. Left: Schematic of optical probe, with DCS/NIRS source–detector pairs in crossed configuration at a fixed separation of 2.5 cm to measure approximately same volume of tissue

Fig. 2

Left: Representative axial slice from bone-windowed, non-contrast CT scan (Pt. 7) showing optical probes on both sides of the forehead (arrows). Right: CBF map from XeCT baseline scan of the same axial slice with ROIs under DCS/NIRS probes outlined

Fig. 3

Scatter plot illustrating the correlation between rCBFDCS and rCBFXeCT calculated from ROIs drawn under the optical probes. The fit line has a slope of 1.1 and an offset of 9.3%

Fig. 4

Example of xenon-enhanced flow activation. Vertical lines indicate the following marks: beginning of baseline CT scan (BL), xenon gas washing in, and lastly end of xenon-CT scan. Measurements from the left and right frontal optical probes are indicated by light gray and dark gray lines, respectively. Once xenon begins to wash in, rCBFDCS in both hemispheres begins to increase (top panel) and elevated CBF is maintained throughout the duration of the scan. ΔTHC increases in both cerebral hemispheres during the scan (middle panel), with a concurrent rise in MAP (bottom panel)