RESUMO
Significance: Near-infrared spectroscopy (NIRS) is a non-invasive optical method that measures changes in hemoglobin concentration and oxygenation. The measured light intensity is susceptible to reduced signal quality due to the presence of melanin. Aim: We quantify the influence of melanin concentration on NIRS measurements taken with a frequency-domain near-infrared spectroscopy system using 690 and 830 nm. Approach: Using a forehead NIRS probe, we measured 35 healthy participants and investigated the correlation between melanin concentration indices, which were determined using a colorimeter, and several key metrics from the NIRS signal. These metrics include signal-to-noise ratio (SNR), two measurements of oxygen saturation (arterial oxygen saturation, SpO 2 , and tissue oxygen saturation, StO 2 ), and optical properties represented by the absorption coefficient ( µ a ) and the reduced scattering coefficient ( µ s ' ). Results: We found a significant negative correlation between the melanin index and the SNR estimated in oxy-hemoglobin signals ( r s = - 0.489 , p = 0.006 ) and SpO 2 levels ( r s = - 0.413 , p = 0.023 ). However, no significant changes were observed in the optical properties and StO 2 ( r s = - 0.146 , p = 0.44 ). Conclusions: We found that estimated SNR and SpO 2 values show a significant decline and dependence on the melanin index, whereas StO 2 and optical properties do not show any correlation with the melanin index.