Alterations of absorption coefficients of tissue water as a result of the heating under the IR FEL radiation with different wavelengths
The effect of temperature dependent shift of water absorption band, known for pure water, has been examined, for the first time, for tissue water, using the IR Free Electron Laser radiation. Cooling kinetics of cartilage and cornea irradiated was measured with a fluorimeter. We have modified the computation algorithm to calculate the optical properties from these measurements more precisely. Temperature dependence of the absorption coefficient of tissue water is studied, for both sides of water absorption bands at 3.0 and 6.1 μm. It is shown that cooling kinetics for samples irradiated with small laser intensity is the same, for both wavelengths of each pair: 6.2 and 6.0; 6.35 and 5.92; 3.22 and 2.81; 3.15 and 2.87 μm. For high laser intensity, the cooling curves are differ, for above wavelengths. From cooling kinetics curves we have calculated the values of absorption coefficient and their alterations for above wavelengths. We have modified the computation algorithm taking into account the real FTIR spectra of the tissue, the effect of water evaporation from the tissue, and specific characteristics of the IR detector used. It is shown that absorption coefficient may increase or decrease depending on laser wavelength and fluence, and that the water absorption bands have a tendency to shift under laser heating. The IR absorption spectra of cartilage and cornea have been measured by the FTIR spectrometer. The limitation and possible errors of two techniques used have been discussed.
Sobol, E; Sviridov, A; Kitai, M; Gilligan, J; Edwards, G
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