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

• Published in: Physics in medicine & biology 2006-01, Vol.51 (1), p.121-136
• Main Authors: Gade, John, Palmqvist, Dorte, Plomgård, Peter, Greisen, Gorm
• Format: Article
• Language: English
• Subjects: Algorithms; Animals; Hemoglobins - chemistry; Humans; Image Interpretation, Computer-Assisted; Light; Models, Chemical; Mucous Membrane - pathology; Oximetry - methods; Oxygen - chemistry; Phantoms, Imaging; Scattering, Radiation; Spectrophotometry - methods; Spectroscopy, Near-Infrared - methods; Swine; Temperature; Tomography, Optical
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/51/1/009

The purpose of the study was to compare algorithms of four methods (plus two modifications) for spectrophotometric haemoglobin saturation measurements. Comparison was made in tissue phantoms basically consisting of a phosphate buffer, Intralipid and blood, allowing samples to be taken for reference measurements. Three experimental series were made. In experiment A (eight phantoms) we used the Knoefel method and measured specific extinction coefficients with a reflection spectrophotometer. In experiment B (six phantoms) the fully oxygenated phantoms were gradually deoxygenated with baker's yeast, and simultaneous measurements were made with our spectrophotometer and with a reference oxymeter (ABL-605) in 3 min intervals. For each spectrophotometric measurement haemoglobin saturation was calculated with all algorithms and modifications, and compared with reference. In experiment C (11 phantoms) we evaluated the ability of a modification of the Knoefel method to measure haemoglobin concentration in absolute quantities using extinction coefficients from experiment A.Results. Experiment A: with the Knoefel method extinction coefficients (+/-SD) for oxyhaemoglobin at 553.04 and 573.75 nm were 1.117 (+/-0.0396) ODmM(-1) and 1.680 (+/- 0.0815) ODmM(-1), respectively, and for deoxyhaemoglobin 1.205 (+/- 0.0514) ODmM(-1) and 0.953 (+/-0.0487) ODmM(-1), respectively. Experiment B: high correlation with the reference was found in all methods (r = 0.94-0.97). However, agreement varied from evidently wrong in method 3 and the original method 4 (e.g. saturation above 160%) to high agreement in method 2 as well as the modifications of methods 1 and 4, where oxygen dissociation curves were close to the reference method. Experiment C: with the modified Knoefel method the mean haemoglobin concentration difference from reference was 8.3% and the correlation was high (r = 0.91). We conclude that method 2 and the modifications of 1 and 4 were superior to the others, but depended on known values in the same or similar phantoms. The original method 1 was independent of results from the tissue phantoms, but agreement was slightly poorer. Method 3 and the original method 4 could not be recommended. The ability of the modified method 1 to measure haemoglobin concentration is promising, but needs further development.