We have investigated the contribution of water in the quantitative determination of hemoglobin concentration and saturation by near-infrared spectroscopy in turbid media. Our study consists of in vitro measurements on an aqueous suspension containing Liposyn, bovine blood, and yeast, buffered at pH 7.2. The optical coefficients of the medium (μa,~0.03-0.08 cm−1, μs′~0 cm−1) match those of biological tissue in the near-infrared, and the hemoglobin concentration (23 μM) is also similar to that found in tissues. We were able to reversibly saturate and desaturate hemoglobin in the full range O-100% by flowing either oxygen or nitrogen through the medium. We found that water absorption must be taken into account to obtain accurate results of hemoglobin concentration and saturation. However, for the two wavelengths employed in this study (715 and 825 nm), the water correction has a small effect on deoxy-hemoglobin concentration, and on hemoglobin saturation in the high saturation limit. Oxy-hemoglobin concentration, and hemoglobin saturation in the low saturation limit are the parameters most sensitive to water correction.
© 1996 Optical Society of AmericaPDF Article