Experimental investigation of NIRS spatial sensitivity

Area of Science:

• Biomedical Optics
• Medical Physics
• Optical Diagnostics

Background:

• Near-infrared spectroscopy (NIRS) shows promise for medical diagnostics, particularly for monitoring hemodynamic changes.
• Clinical interpretation of NIRS signals is hindered by uncertainties regarding their origin, especially in living tissues.
• A clear understanding of NIRS signal origins requires rigorous combined theoretical and experimental studies.

Purpose of the Study:

• To experimentally investigate the spatial sensitivity of near-infrared optical measurements.
• To establish the relationship between spatial changes in optical properties and NIRS signal variations.
• To provide a foundation for reliable clinical interpretation of NIRS data.

Main Methods:

• Utilized a liquid optical phantom as a tissue-equivalent model.
• Employed a robot-controlled system to introduce localized perturbations in optical properties.
• Performed trans-illumination/reflection measurements using a NIRS instrument.
• Compared experimental sensitivity data with numerical simulations.

Main Results:

• Investigated the influence of optical properties and source-detector distances on spatial sensitivity distribution.
• Developed sensitivity maps that can define characteristic parameters, such as penetration depth.
• Demonstrated good agreement between experimentally derived penetration depth and published values using a 25% threshold.

Conclusions:

• This work presents the first experimental study of NIRS spatial sensitivity.
• The developed experimental method allows in-depth investigation of factors influencing NIRS measurements, including tissue optical properties and source-detector configurations.
• This approach is crucial for advancing the clinical application and interpretation of NIRS technology.