Modelling the sampling volume for skin blood oxygenation measurements

Area of Science:

• Biomedical Optics
• Photonic Measurements
• Dermal Physiology

Background:

• Quantifying hemoglobin skin saturation is challenging due to variable blood content and distribution.
• Identifying the specific vascular bed contributing to optical signals is crucial for accurate measurements.
• Understanding spatial detector depth sensitivity guides the selection of optimal fiber-optic probe geometries.

Purpose of the Study:

• To develop a Monte Carlo simulation to estimate the sampling volume of fiber-optic probes.
• To investigate the impact of source-detector spacing on skin layer sampling.
• To model skin optics using optical properties of Caucasian skin in the visible spectrum.

Main Methods:

• Monte Carlo simulation to model photon transport in skin.
• Utilized optical properties of Caucasian skin tissue.
• Simulated fiber-optic probes with source-detector spacings of 250, 400, and 800 micrometers.

Main Results:

• Small source-detector spacings (≤800 microm) are significantly influenced by rough refractive index boundaries.
• Wavy interfaces between skin layers promote deeper, more homogeneous photon distribution.
• Probe spacing determines sampled skin layers: 250 microm for epidermis/papillary dermis, 400-800 microm for dermal layers.

Conclusions:

• Monte Carlo simulations effectively estimate fiber-optic probe sampling volumes in skin.
• Skin layer interface characteristics and probe geometry critically affect optical measurements.
• Optimized probe spacing is essential for targeting specific vascular beds in the skin for accurate saturation analysis.