Geometric decoupling of epidermal melanin and dermal hemoglobin signals using coaxial and spatially resolved NIRS.

SIGNIFICANCE: Epidermal melanin can confound NIRS measurements of tissue oxygen saturation and reduce accuracy across skin tones.

AIM: We evaluated whether a coaxial detector can provide a superficial reference that improves absolute StO 2 estimation when combined with spatially resolved measurements.

APPROACH: Monte Carlo simulations of multilayer skin were evaluated using mutual information and XGBoost regression, with entire melanin levels held out during validation. Three detector configurations were compared: coaxial only, surface only, and the combined geometry. A secondary experimental analysis examined absolute and baseline referenced oxygenation prediction using validation that excluded one recording at a time.

RESULTS

The combined coaxial plus surface detector configuration reduced average StO 2 RMSE from 11.34 to 5.41 percentage points, corresponding to a 52.3% relative reduction based on the displayed fold results. Mutual information analysis showed that the coaxial detector carried substantial information about melanin while carrying negligible direct information about StO 2 . In the experimental analysis, baseline-referenced features improved pooled agreement, but the recording-based validation did not establish generalization to entirely unseen participants.

CONCLUSIONS

These findings support future experimental validation of integrated coaxial plus spatially resolved probes for melanin-robust absolute tissue oxygenation monitoring.