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J. Eur. Opt. Society-Rapid Publ. 22, 48( 2026) photons remain ballistic, hair follicles extend deep into the dermal and muscular layers. At these depths, the high scattering coefficient of the surrounding turbid media induces a rapid transition to the diffusive regime, effectively homogenizing the influence of such microstructures [ 42, 43, 47 ]. Consequently, the proposed cascaded framework prioritizes the skin pore as the dominant structural variable affecting initial photon angular distribution before the onset of bulk scattering. Despite these simplifications, the use of MRIsegmented cadaveric head models preserves anatomical realism at the macroscopic scale, while the cascaded implementation of ballistic photon propagation and diffusive photon transport regimes provides a mechanistically consistent framework for interpreting how pore-scale surface features influence subsequent photon transport. Finally, direct experimental validation of pore-scale optical coupling effects would require the fabrication of skin-mimicking phantoms with tightly controlled sub-millimeter surface microgeometry and well-defined optical properties. Developing such phantoms represents a substantial experimental challenge and therefore remains beyond the scope of the present computational study.
Future studies should focus on further refining the model by extending the ballistic photon propagation simulations to fully 3D geometries with multiple pore configurations and more realistic surface roughness. This would allow a more faithful representation of the stochastic nature of skin microtopography, provided that pore locations are spatially distributed to intercept the emitted photon bundle within the optical source half-angle of 70 °, rather than representing arbitrary multiplicity without optical relevance. Including deep structures like hair follicles, would enable assessment of their complex geometry and contribution to photon transport. Integrating spatially varying optical properties and dynamic surface coupling conditions could further enable assessment of physiological variability under realistic measurement scenarios. Additionally, direct experimental validation remains necessary to confirm pore-scale optical coupling effects.
5 Conclusion
This study investigated the influence of skin pore microgeometry NIR photon transport within anatomically realistic, MRI-segmented cadaveric head models using a cascaded simulation framework that links ballistic photon propagation at the source – scalp interface with subsequent diffusive photon transport in deeper tissues. By explicitly resolving pore-scale surface structures during the ballistic phase and propagating the resulting photon states into diffusive transport simulations, the present work provides a multiscale framework for evaluating how microscopic surface features influence macroscopic photon propagation.
Skin pore microgeometry introduces localized perturbations during the ballistic photon propagation phase, increasing photon angular divergence and reducing forward-directed energy delivery toward deeper tissues. However, due to the strongly scattering nature of scalp and skull tissues, these directional perturbations are rapidly randomized within the first few millimeters of propagation and therefore do not measurably alter DS profiles or photon path statistics in the diffusive regime. In contrast, the pore-induced reduction in photon weights represents a persistent loss of incident optical energy that directly modulates the total photon budget available for transport through deeper tissue layers. At the system level, this attenuation affects both reflective and transmissive-mode optical configurations, although its impact may become more pronounced in transmissive geometries where photons traverse longer tissue paths. Collectively, these findings indicate that pore-scale surface microgeometry primarily influences optical coupling efficiency rather than the stochastic characteristics of photon transport, providing practical guidance for the modeling and design of biomedical optical measurement systems.
Acknowledgments
The authors gratefully acknowledge Acibadem Mehmet Ali Aydınlar University for supporting this research. The authors also thank MD Baran Bozkurt( Department of Neurosurgery and Neuroanatomy Laboratory, School of Medicine, Acibadem Mehmet Ali Aydınlar University, Istanbul, Türkiye) for providing the facilities used for the MRI of cadaveric heads acquired in a previous study, which were utilized in the present work.
Funding
This work was supported by Acibadem Mehmet Ali Aydınlar University General Research Fund with Grant Number FBA20232164.
Conflicts of interest The authors have nothing to disclose.
Data availability statement
Data associated with this article are available from the corresponding author upon reasonable request.
Author contribution statement
Conceptualization, S. I. Y.; Methodology, S. I. Y.; Software, S. I. Y.; Validation, S. I. Y.; Formal Analysis, S. I. Y.; Resources, M. E. A.; Data Curation, S. I. Y.; Writing – Original Draft Preparation, S. I. Y.; Writing – Review & Editing, S. I. Y. and M. E. A.; Visualization, S. I. Y.; Supervision, M. E. A.; Project Administration, M. E. A.
Ethics approval
This study did not involve new human or animal experiments. All cadaveric MRI data used in this work were acquired as part of a previously published study [ 22 ], for which ethical approval and informed consent procedures were obtained and are described in detail in the original publication. The present study exclusively reuses these previously approved and published data.
Supplementary material
Section A: Magnetic Resonance Imaging – Derived Cadaveric Head Anatomy. Section B: Ballistic Photon Propagation Simulations. Section C: Diffusive Photon Transport Simulations. The supplementary material of this article is available at https:// jeos. edpsciences. org / 10.1051 / jeos / 2026044 / olm.