Casey M. Ladtkow

Material Removal Mechanisms in Monopolar Electrosurgery

The underlying mechanisms that cause the observed tissue differences in monopolar electrosurgery under different electrical excitation conditions have not been accurately identified to date. Without an understanding of the mechanisms behind the observed differences in tissue effect, advances in electrosurgical technology are reduced to empirical trial and error. The numerical method we present herein allows single arc events and two ensuing vaporization mechanisms and thermal damage to surrounding tissues to be modeled. It also allows for a realistic prediction of the effect of different electrical waveforms employed in monopolar electrosurgery. The method presented here models both explosive boiling and confined boiling as mechanisms for observed material removal. It uses an Arrhenius damage calculation to predict both tissue cutting rates and adjacent thermal damage to peripheral tissue. All results agree with experimentally observed results. To our knowledge this agreement has not been accomplished with previous models. While not a complete description of the physical events surrounding tissue division and coagulation in electrosurgery, modeling single arc events is the initial step towards understanding the mechanisms of monopolar electrosurgery.

Modeling bimodal vessel effects on radio and microwave frequency ablation zones

A bench liver model is presented that separates the thermal and electrical effects of large blood vessels within radio and microwave frequency ablation boundaries. The model includes a cylindrical tissue environment with a 5 mm vessel placed parallel to and 15 mm way from either a Covidien Energy-based Devices EvidentTM MW Ablation Percutaneous Antenna or a CoolTipTM RF Ablation Single Electrode Kit. An array of fiber optic thermal probes is used to monitor radial temperature profile on the vessel and non-vessel sides of the ablation zone. Circulating blood exhibits higher electrical conductivity than surrounding liver tissue and provides a significant means for transport of thermal energy. Data from the thermal probes indicate key performance differentiators between MW and RF ablation modalities when they are used next to large blood vessels clarifying the difference between thermal and electrical energy sink. The results suggest RFA is susceptible to both the thermal and electrical energy sink effects of large vasculature while MWA is only susceptible to thermal sink. Ablation zone boundaries were distorted on both the vessel and non-vessel sides with RFA whereas with MWA only the vessel side is affected.