Application Note

THERMAL ANALYSIS OF MICROWAVE ABLATION BY A COAXIAL OPEN-TIP ANTENNA

RF Microwave ablation based on thermal therapies is an attractive solution for large soft tissues within a short treatment period. it produces rapid heat generation from an electromagnetic Open-tip applicator, sufficient to trigger an instant tissue coagulation and necrosis which will be tightened and reduced in size. This technique can be used to treat sleep disorder syndromes such snoring. Radio frequency based surgery has received increased attention due to its minimal postoperative pain and complications with a shorter recovery time.

This process relies on an absorption power, time and temperature distribution of microwave energy. Estimation of those factors using simulation solver seems to be a promising way in microwave ablation system design. In this study, an FEM multiphysics simulation using HFWorks of this process is presented, by an Open-tip antenna applicator introduced inside the soft palate tissue CAD model.

The introduced Applicator Design is a Coaxial antenna type providing a bending tip extremity to consider the anatomy of human mouth cavity and the curved region of the upper soft palate tissue. Figure 1 shows the modeled antenna design.

Figure 1 - Soft Palate model with the open-tip antenna

HFWorks comes with an integrated thermal solver that allows to predict the thermal aspects of the studied High frequency design due to conductor and dielectric losses under different power excitation loads. For the case of studied Microwave ablation process, an excitation power of Pin=50W was used in heating the soft palate tissue. The simulation revealed the next results at frequency of 2.45GH.

Figure 2 - (a-Electric and (b-Magnetic field distribution at 2.45GHz

A steady state thermal analysis coupled to the antenna study gives the next temperature results: Figure 3 shows the temperature distribution in soft tissue due to heat generated from antenna at 2.45GH. Regions with highest temperature are focused along the perimeter of the opened-tip antenna part with a maximum value of 54°C. The coagulated zones of the studied tissue can be estimated from the obtained temperature distribution.

Figure 3 - (a-Fringe plot and (b- Iso-clipping plot of temperature distribution at 2.45GHz.