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

BACKGROUND

Absolute optical properties (i.e., the absorption coefficient, μ, and the reduced scattering coefficient, [Formula: see text]) of head tissue can be measured with frequency-domain near-infrared spectroscopy (FD-NIRS).

AIM

We investigated how the absolute optical properties depend on the individual subject and the head region.

MATERIALS AND METHODS

The data set used for the analysis comprised 31 single FD-NIRS measurements of 14 healthy subjects (9 men, 5 women, aged 33.4 ± 10.5 years). 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 μ and [Formula: see text] as well as the effective attenuation coefficient (μ) and the differential pathlength factor (DPF). The measurement was done for each subject one to three times with at least 24 h between the measurements.

RESULTS

(i) A Bayesian ANOVA analysis revealed that head region and subject were the most significant main effects on μ, [Formula: see text] and μ, as well as DPF, respectively. (ii) At the VC, μ, [Formula: see text] and μ 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.

DISCUSSION AND CONCLUSION

Our analysis demonstrates that all optical head tissue properties (μ, [Formula: see text], μ 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.