Thermal Damage due to a Monopole Microwave Antenna

In vivo thermal damage was estimated due to a monopole microwave antenna placed inside a perfused muscle-like tissue as a function of the resonant microwave frequency (i.e. 915MHz, 2.45, and 5.8GHz), peak tissue temperature (i.e. ~60, ~80, and ~100°C), and heating duration (i.e. 1, 2, 3, 5, 10, and 15 minutes). For comparison, the thermal damage was also computed for a given total absorbed power (i.e. 5, 10, 20, 50, 100W) for the heating duration of 10 minutes assuming that the tissue temperature was constrained to ~110°C due to steaming. Necessary power density distribution was computed from the electromagnetic fields determined by solving Maxwell equations. The associated tissue heating was computed by solving the previously validated, first principles-based Generic Bioheat Transfer Model. Induced thermal damage was estimated by (i) computing thermal dose per cumulative equivalent minutes at 43°C and setting the dose damage threshold as CEM43 ≥60 min; (ii) computing thermal dose per the Arrhenius equation and setting the dose damage threshold as Ω ≥1; and (iii) setting damaging temperature threshold as ≥55°C. Results showed that, first, significantly larger thermal damage could be induced by controlling total input power instead of peak tissue temperature. Second, controlling peak tissue temperature below 100°C induced relatively more spherical damage irrespective of the frequency. Third, when input power was controlled (instead of the peak tissue temperature), the induced damage became relatively more spherical with the increase in the MW frequency. Fourth, the three thermal damage metrics may produce significantly different damage. Fifth and finally, when comparing the induced thermal damage with the previously published measured thermal damage, it appeared that, typically, the mean induced damage lay in between the range of damage predicted by the Arrhenius and CEM43 methods and was comparable to the damage predicted by the thermal threshold method.