Desenvolvimento de um eletrodo expansível de níquel-titânio para ablação hepática por radiofrequência

Development of an expandable electrode of nickel titanium for Radiofrequency Ablation Author: MARINA PINHEIRO MARQUES Supervisor: Prof(a). Dra. Suélia de Siqueira Rodrigues Fleury Rosa Post-Graduation Program in Biomedical Engineering – Thesis of Master Degree Brasília, September of 2016. Hepatocellular carcinoma is a type of liver tumor with high death rates around the world. When it is diagnosed at an early stage, tumor nodules of up to 3cm can be treated by radiofrequency ablation (RFA). This procedure is carried out through a minimally invasive incision to insert an electrode which is image-guided to the location of the tumor and delivers an alternate high-frequency current to the tissue, causing cellular necrosis at around 45∘C-60∘C. In spite of offering little damage and low risk of complications when compared to other treatments, RFA is not often used in Brazil because of its elevated costs and because there are only few professionals that are trained to perform it. This paper presents the development and analysis of an active monopolar electrode that is to be attached to the SOFIA equipment for hepatic RFA developed in the Biomedical Engineering Laboratory of the University of Brasília. In addition, the paper proposes a relation between the potency and geometry of the electrode to ensure the zone of ablation and that the roll-off will happen, which is an event characterized by the precipitous variation of impedance after necrosis, with and without accelerators (solutions of anhydrous alcohol and acetic acid) injected to quicken the burn. An umbrella electrode, active and monopolar, was built with nickel titanium and micro welding by laser of Yb fiber. For the evaluation of the electrode, the analysis of the solder by scanning electron microscope was carried out. For its validation, ex vivo tests were performed on bovine livers, with comparisons of dimensions of larger width, narrow width and depth of the ablation zone obtained with 8 other electrosurgery electrodes. Through a blind experiment, only 4 electrodes were chosen to evaluate the combinations of 40W and 80W of potency at 400kHz per 10min, 20min and 30min. Simulations of the umbrella electrode model with 5 electrodes (5H) were performed in the COMSOL software and compared to the ex vivo results. And due to the difference of properties between live and ex-vivo tissue, a mathematic modeling with and adapted Cole-Cole model was made to evaluate the influence of impedance on the developed 5H umbrella electrode. The manufacturing process used in this work can reduce up to 10x the cost of the active electrode. The experiments that tested the electrode showed that with potency of 40W for up to 30min it is possible to burn a volume of up to 25cm3. We found that the geometry delays the roll-off and consequently produces larger and better-defined ablation zones than any other electrode that was tested. Between the accelerators, anhydrous alcohol combined with RFA is potentially more helpful in tumor necrosis. This study found that tissue impedance influences the electrical density and that is why a variation between the ablation produced on in vivo and post mortem tissues exists. Key-words: Radiofrequency Ablation, Electrode, NiTi, Liver, Cole Cole.