Prediction of sampling depth and photon pathlength in laser Doppler flowmetry

Area of Science:

• Biomedical Optics
• Medical Imaging
• Photonics

Background:

• Laser Doppler flowmetry (LDF) is crucial for non-invasive tissue perfusion measurement.
• Understanding photon migration in tissue is essential for LDF accuracy.
• Monte Carlo simulations offer a robust method for modeling light-tissue interaction.

Purpose of the Study:

• To assess sampling depth, measuring depth, and photon pathlength in LDF using Monte Carlo simulations.
• To evaluate the impact of different probe geometries on these parameters.
• To investigate tissue-specific variations (skin, liver, brain) and their influence on LDF measurements.

Main Methods:

• Utilized Monte Carlo simulation to model photon migration through various tissue models.
• Calculated median sampling depth and photon pathlength for different fiber probe configurations.
• Varied fiber separation and simulated different tissue optical properties (g-value, scattering coefficient).

Main Results:

• Shallowest median sampling depth of 68 microns achieved with a 120-micron single fiber probe on skin.
• Increased fiber separation from 250 to 700 microns enhanced median sampling depth from 146 to 233 microns.
• Liver tissue exhibited shallower sampling depth, while brain tissue showed deeper sampling compared to skin.
• Homogeneous blood volume had a limited impact (approx. 1%) on skin tissue sampling depth.

Conclusions:

• Probe geometry, particularly fiber separation, significantly influences LDF sampling depth and photon pathlength.
• Tissue optical properties (g-value, scattering) dictate tissue-specific sampling depths.
• Optimizing probe design and understanding tissue properties are critical for accurate LDF measurements and perfusion profiling.