JEOS RP ISSN03 | Page 484

J. Eur. Opt. Society-Rapid Publ. 22, 48( 2026) 477

Table 2. Summary of detected photon statistics across eight cadaveric head models for two vertical pore alignments. The data highlights the inter-subject variability in total photon counts and mean photon weights relative to the systematic shifts induced by sub-millimeter changes in pore proximity.

Figure 5. Box plots for detected photon counts across eight cadaveric heads at two distinct vertical pore positions: 1, and 0.5 mm off-axis relative to the optical source center.

Figure 6. Box plots for detected mean photon weight across eight cadaveric heads at two distinct vertical pore positions: 1, and 0.5 mm off-axis relative to the optical source center. layer( 16.1 mm) likely facilitates increased lateral light piping, reducing the fraction of photons returning to the scalp [ 44 ]. This reinforces that while pore-scale features introduce systematic perturbations, large-scale anatomical variations remain the primary determinants of the absolute photon budget. From a system design perspective, these findings indicate that while explicit incorporation of skin pores is unlikely to influence the stochastic characteristics of diffusive transport, the resulting energy loss introduces a localized, systematic bias. This effect is most relevant for highprecision topographic mapping [ 45 ] or longitudinal fNIRS monitoring, where pore-induced attenuation could be misinterpreted as regional cortical variation or altered sensitivity if not accounted for during probe placement [ 46 ]. While this study focuses on reflective-mode optical systems, these findings suggest that surface-induced intensity fluctuations could also be relevant in transmissive-mode configurations, where photons traverse different tissue paths. In such geometries, the initial loss of photon energy at the source – scalp interface may represent a significant factor in the overall link budget. However, as the current study does not explicitly model transmissive geometries, the relative magnitude of these effects remains a hypothesis to be explored in future work.

Certain limitations of the present study should be acknowledged. First, the ballistic photon propagation simulations were performed in 2D using idealized elliptical pore geometries, with surface roughness introduced by applying Gaussian noise to the pore boundaries. While this approach captures key geometric perturbations, it cannot fully represent the 3D complexity of real skin microtopography. Furthermore, while a typical NIR optical source diameter( e. g., 5 mm) simultaneously illuminates a multi-pore array, the present work utilizes a single-pore configuration to isolate the fundamental mechanistic influence of pore geometry. While the aggregate effect of hundreds of pores across a wide source footprint would likely result in spatial averaging of the energy loss, the single-pore model established here serves as a necessary unit analysis to characterize the maximum potential perturbation at the source – scalp interface. Second, during the diffusive photon transport simulations, tissue optical properties were assumed to be homogeneous within each segmented anatomical layer and implemented within a graded-media framework. Consequently, dynamic physiological factors such as variations in skin hydration, local optical coupling conditions, and temporal changes in tissue optical properties were not considered. The inclusion of complex pilosebaceous units such as hair follicles or sebum was excluded from the present study to maintain a focused analysis on the primary source – scalp interface. Unlike surface skin pores, which create discrete geometric perturbations at the immediate point of entry where