Optical properties of human blood as a function of temperature

Knowledge of optical and thermal properties of human tissue is essential for optimization of laser theraphy and optical diagnostics. Published data is in genereal incomplete, and there is very limited information on the temperature dependence of optical properties. The temperature dependence of hemoglobin is important since it is the target chromophore for laser treatment of e.g. port-wine stains. The present study emphasizes the temperature dependence of the hemoglobin absorption. Erythrocyte concentrate was heated in a water bath, hemolyzed with distilled water and centrifuged before absorption spectra was collected. Measurements were performed in the range 50-80 degrees Celsius. Penetration depth measurements of the heated erythrocyte concentrate were done at 488 nm, 585 nm, 590 nm and 630 nm. For these measurements the erythrocytes were mixed with a highly scattering material (whole milk). The hemoglobin absorbance demonstrates a characteristic change during heating. This change is partly due to oxidative reactions with formation of met-hemoglobin, and also by protein denaturation. The change in the absorption coefficient due to met-hemoglobin has a maximum at approximately 72 degrees Celsius, where the increase was measured up to 200% at 630 nm wavelength.