Phase dual‐slopes in frequency‐domain near‐infrared spectroscopy for enhanced sensitivity to brain tissue: First applications to human subjects

• Published in: Journal of biophotonics Vol. 13; no. 1; pp. e201960018 - n/a
• Main Authors: Blaney, Giles, Sassaroli, Angelo, Pham, Thao, Fernandez, Cristianne, Fantini, Sergio
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag GmbH & Co. KGaA 01.01.2020; Wiley Subscription Services, Inc
• Subjects: Blood; Blood flow; Blood Flow Velocity; Blood pressure; Blood volume; Brain; Cerebral cortex; Cerebrovascular Circulation; coherent hemodynamics; diffuse optics; Diffusion theory; Flow velocity; Forehead; functional brain imaging; Hemodynamics; Human subjects; Humans; Infrared spectroscopy; near‐infrared spectroscopy; Oscillations; photon‐density waves; Pressure oscillations; Qualitative analysis; Research Subjects; Scalp; Sensitivity enhancement; Slopes; Spectroscopy, Near-Infrared; Spectrum analysis; near-infrared spectroscopy; diffuse optics; photon-density waves; functional brain imaging; coherent hemodynamics
• ISSN: 1864-063X; 1864-0648; 1864-0648
• DOI: 10.1002/jbio.201960018

We present a first in vivo application of phase dual‐slopes (DSϕ), measured with frequency‐domain near‐infrared spectroscopy on four healthy human subjects, to demonstrate their enhanced sensitivity to cerebral hemodynamics. During arterial blood pressure oscillations elicited at a frequency of 0.1 Hz, we compare three different ways to analyze either intensity (I) or phase (ϕ) data collected on the subject's forehead at multiple source‐detector distances: Single‐distance, single‐slope and DS. Theoretical calculations based on diffusion theory show that the method with the deepest maximal sensitivity (at about 11 mm) is DSϕ. The in vivo results indicate a qualitative difference of phase data (especially DSϕ) and intensity data (especially single‐distance intensity [SDI]), which we assign to stronger contributions from scalp hemodynamics to SDI and from cortical hemodynamics to DSϕ. Our findings suggest that scalp hemodynamic oscillations may be dominated by blood volume dynamics, whereas cortical hemodynamics may be dominated by blood flow velocity dynamics. We report simulations and first measurements on the human brain with a new frequency‐domain near‐infrared spectroscopy (NIRS) technique based on phase dual‐slopes (DSϕ). The DSϕ technique requires two light sources and two optical detectors placed on the tissue surface in a special configuration, and a dedicated data analysis scheme. Our results indicate the deeper region of sensitivity of DSϕ measurements compared with existing NIRS measurement approaches, with a maximal sensitivity at a depth of about 11 mm.