Near-infrared spectroscopy: a methodology-focused review

Area of Science:

• Biomedical Engineering
• Optical Physics
• Physiology

Background:

• Near infrared spectroscopy (NIRS) is a non-invasive optical technique for monitoring tissue oxygen status.
• NIRS has gained prominence due to its portability, ease of use, and applicability in diverse research and clinical settings.
• Traditional NIRS methods, based on the Beer-Lambert law, primarily offer trend monitoring of tissue oxygenation from an arbitrary baseline.

Purpose of the Study:

• To review the physical principles underlying tissue spectroscopy using NIRS.
• To describe the evolution of NIRS technology, including instruments providing continuous absolute measurements.
• To discuss theoretical details, experimental procedures, and data analysis for NIRS measurements of physiological variables.

Main Methods:

• Review of physical principles of NIRS and tissue spectroscopy.
• Description of various NIRS operating principles, both current and developmental.
• Explanation of theoretical frameworks, experimental protocols, and data analysis techniques for NIRS.

Main Results:

• NIRS technology has evolved from trend monitoring to providing continuous absolute regional hemoglobin saturation values.
• Refinements have enhanced NIRS applicability across various research and clinical environments.
• The review details the physical basis, operational modes, and analytical methods for NIRS.

Conclusions:

• NIRS is a versatile tool for monitoring tissue oxygen status with increasing quantitative capabilities.
• Technological advancements have significantly broadened the scope and accuracy of NIRS applications.
• Future research directions and the potential of NIRS beyond its current applications are discussed.