Absolute Values of Optical Properties (μa, μ΄s, μeff and DPF) of Human Head Tissue: Dependence on Head Region and Individual.

Abstract

Absolute optical properties (i.e., the absorption coefficient, μa, and the reduced scattering coefficient, [Formula: see text]) of head tissue can be measured with frequency-domain near-infrared spectroscopy (FD-NIRS). We investigated how the absolute optical properties depend on the individual subject and the head region. The data set used for the analysis comprised 31 single FD-NIRS measurements of 14 healthy subjects (9 men, 5 women, aged 33.4 ± 10.5years). From an 8-min measurement (resting-state; FD-NIRS device: Imagent, ISS Inc.; bilateral over the prefrontal cortex, PFC, and visual cortex, VC) median values were calculated for μa and [Formula: see text] as well as the effective attenuation coefficient (μeff) and the differential pathlength factor (DPF). The measurement was done for each subject one to three times with at least 24h between the measurements. (i) A Bayesian ANOVA analysis revealed that head region and subject were the most significant main effects on μa, [Formula: see text] and μeff, as well as DPF, respectively. (ii) At the VC, μa, [Formula: see text] and μeff had higher values compared to the PFC. (iii) The differences in the optical properties between PFC and VC were age-dependent. (iv) All optical properties also were age-dependent. This was strongest for the properties of the PFC compared to the VC. Our analysis demonstrates that all optical head tissue properties (μa, [Formula: see text], μeff and DPF) were dependent on the head region, individual subject and age. The optical properties of the head are like a 'fingerprint' for the individual subject. Assuming constant optical properties for the whole head should be carefully reconsidered.