Multivariate reference technique for quantitative analysis of fiber-optic tissue Raman spectroscopy

Area of Science:

• Biomedical Optics
• Spectroscopy
• Medical Diagnostics

Background:

• Quantitative analysis of in vivo tissue Raman spectroscopy is crucial for accurate medical diagnostics.
• Variations in laser excitation power and fiber coupling efficiency can affect Raman signal intensity and reliability.
• Existing univariate methods for correcting these variations are less effective.

Purpose of the Study:

• To develop and evaluate a novel multivariate reference technique for real-time quantitative analysis of in vivo tissue Raman measurements.
• To improve the accuracy and standardization of tissue Raman spectroscopy by correcting for laser power and fiber coupling variations.
• To demonstrate the applicability of this technique in challenging settings, such as Raman endoscopy.

Main Methods:

• Utilized multivariate reference signals from fused silica and sapphire within a ball-lens fiber-optic Raman probe.
• Applied Partial Least-Squares (PLS) regression modeling to extract internal reference Raman signals.
• Evaluated the technique using in vivo oral tissue measurements (n=25) and gelatin tissue phantoms.

Main Results:

• Achieved accurate prediction of laser excitation power changes with a leave-one-subject-out cross-validation (R(2)=0.981, RMSECV=2.5 mW), outperforming univariate methods (RMSE=6.2 mW).
• Demonstrated real-time laser power prediction with an RMSEP of 2.4 mW (R(2)=0.985) on new subjects.
• Quantified gelatin tissue phantoms with an RMSEP of ~2.0% (R(2)=0.998), independent of laser power variations.

Conclusions:

• The multivariate reference technique effectively monitors and corrects in situ variations in laser excitation power and fiber coupling efficiency.
• This method standardizes tissue Raman intensity, enabling reliable quantitative analysis for in vivo applications.
• The technique shows significant promise for advancing quantitative Raman spectroscopy, particularly in endoscopic settings.