title: Diffuse reflectance spectrophotometry with visible light: comparison of four different methods in a tissue phantom.
abstract: 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.
authors.affiliation: Department of Cardiothoracic Surgery RT, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. johngade@get2net.dk
authors.forename: John
authors.initials: J
authors.lastname: Gade
authors.forename: Dorte
authors.initials: D
authors.lastname: Palmqvist
authors.forename: Peter
authors.initials: P
authors.lastname: Plomgård
authors.forename: Gorm
authors.initials: G
authors.lastname: Greisen
mesh_terms: D000465:Algorithms; D000818:Animals; D006454:Hemoglobins / Q000737:chemistry; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008027:Light; D008956:Models, Chemical; D009092:Mucous Membrane / Q000473:pathology; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000737:chemistry; D019047:Phantoms, Imaging; D012542:Scattering, Radiation; D013053:Spectrophotometry / Q000379:methods*; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D013552:Swine; D013696:Temperature; D041622:Tomography, Optical
chemical_list: D006454:Hemoglobins; D010100:Oxygen