Change of Attenuation Coefficient due to BOLD

The blood-oxygen-level-dependent (BOLD) effect in neuroimaging reflects changes in magnetic susceptibility due to variations in oxy- and deoxyhemoglobin concentrations. In optical modalities like fNIRS, analogous hemodynamic changes manifest as a variation in the optical attenuation coefficient (μ_t), driven by shifts in absorption (Δμ_a) and scattering (Δμ_s') properties of cerebral tissue. Neural activation increases cerebral blood volume and oxygenation, altering these optical coefficients and modulating the detected light intensity.

Quantitative assessment of this effect relies on solving the inverse problem: converting raw intensity fluctuations into Δμ_a and Δμ_s' values using diffusion models or time-resolved measurements. These parameters enable mapping of cortical activation by distinguishing physiological signals from confounding factors such as superficial tissue dynamics.