Diffuse reflectance spectrophotometry with visible light: comparison of four different methods in a tissue phantom

Area of Science:

• Biomedical Engineering
• Analytical Chemistry

Background:

• Accurate spectrophotometric measurement of hemoglobin saturation is crucial for clinical diagnostics.
• Existing algorithms for spectrophotometric analysis vary in accuracy and reliability.

Purpose of the Study:

• To compare the performance of four spectrophotometric hemoglobin saturation measurement algorithms and two modifications.
• To evaluate the accuracy and agreement of these algorithms against a reference oxymeter using tissue phantoms.

Main Methods:

• Development and testing of tissue phantoms containing phosphate buffer, Intralipid, and blood.
• Measurement of specific extinction coefficients for oxy- and deoxyhemoglobin using the Knoefel method.
• Comparative analysis of spectrophotometric measurements against a reference oxymeter (ABL-605) at 3-minute intervals.
• Evaluation of a modified Knoefel method for absolute hemoglobin concentration measurement.

Main Results:

• High correlation (r=0.94-0.97) was observed between all tested methods and the reference.
• Method 2 and modifications of methods 1 and 4 demonstrated high agreement with reference oxygen dissociation curves.
• Method 3 and the original method 4 showed significant inaccuracies, while the modified Knoefel method for hemoglobin concentration yielded an 8.3% mean difference from reference.

Conclusions:

• Method 2 and modified methods 1 and 4 are superior for spectrophotometric hemoglobin saturation measurement, though dependent on phantom-specific data.
• The original method 1 offers independence but slightly lower agreement.
• Method 3 and original method 4 are not recommended; further development is needed for the modified Knoefel method's hemoglobin concentration measurement capability.