Modulation of optical heating during hyperthermia for the separation of reversible and irreversible changes in...

Preoperative planning of medical attention is crucial in minimally-invasive laser, microwave and radiofrequency treatments. For this purpose, it is important to determine accurately the parameters of biological tissues that describe its changes that occur during hyperthermia procedures. A method providing spatially uniform heating was developed during which changes in the modulus of the electrical admittance of the sample at a frequency of 10 kHz corresponding to the β-dispersion region which is most sensitive to degradation processes were recorded. Highly sensitive fiber Bragg gratings were used for temperature measurements. Amplitude modulation of optical radiation power (20 W at 970 nm) enabled the separation of reversible and irreversible changes occurring during the heating process. Reversible changes are related to the temperature dependence of the ionic conductivity, and irreversible ones are related to cell lysis and protein coagulation. Experimental data were obtained for chicken liver samples. The data were analyzed using the Arrhenius formalism describing the irreversible degradation process of biological tissue. The values of the critical temperature T_cr=101±2°С and the logarithm of the frequency factor ln(A)=(48.5±3.8)ln⁡(s^-1) were obtained.