Dual-slope techniques for frequency-domain NIRS and oscillatory cerebral hemodynamics

Dual-slope techniques in diffuse optics are highly insensitive to instrumental factors and to the optical coupling with the examined tissue, while providing preferential sensitivity to deeper vs. superficial tissue. We will present non-invasive applications of dual-slope frequency-domain near-infrared spectroscopy (FD-NIRS) to the measurement of cortical hemodynamics elicited by visual stimulation or by modulation of arterial blood pressure. The functional measurements show the typically greater cortical sensitivity of dual-slope vs. single-distance data, and phase vs. amplitude data. The measurements of cortical hemodynamics elicited by arterial blood pressure modulation show the qualitative difference between deeper (cerebral) and superficial (scalp) hemodynamics.