Elzbieta Ewertowska

Radiofrequency (RF) ablation has become an important ablative technique widely used in the area of minimally invasive therapies of the modern medicine. The advancement in the field of RF-based technologies over the years has led to a growing number of applications in different therapeutic areas such as cardiac arrhythmias, epilepsy, oncology, assisted resection, apnea, pain or aesthetic surgery. There is, however, a constant need for the development of computer and experimental studies, which would enhance the performance and safety of these techniques.
The main focus of this PhD Thesis was on examining the thermal and electrical phenomena behind tissue radiofrequency ablation in order to improve the efficacy and safety of the RF-based therapies and applicators. Two main areas of interest were pain management and oncology, which were organized into three independent studies. The research methodology was based on computer modeling and experimental studies on phantoms, ex vivo and in vivo models, and clinical trials.
The research on pain management involved the analysis of electrical and thermal effects of the pulsed radiofrequency (PRF) treatment and the related risk of tissue thermal damage. Different pulse protocols used in clinical practice were studied using computer modeling and the study accuracy was validated by means of agar phantom model. Additional computer models for alternative pulse protocols were also proposed, in which thermal effect would be reduced but the electrical effect would remain unchanged. The study also discussed the concept of a mild electroporation from PRF. In the area of oncology, two different techniques were analyzed. First study focused on examining tissue hydration technique during RF ablation with a novel internally cooled wet (ICW) electrode. The new design involved two expandable perfusion needles built into the catheter.
The main aim was to improve the accuracy of computer model of tumor RF ablation using a realistic geometry of saline distribution in tissue, and to assess the performance of the RF catheter. Different cases of saline-infused tumor were modeled and the simulated results were compared with the clinical data from a trial on 17 hepatic cancer patients. An in vivo study on pig liver model was used to obtain a realistic spatial distribution of the infused saline. The second study focused on the development of a new catheter-based endoluminal sealing technique as more effective alternative for management of the pancreatic stump. The method consisted of the impedance-guided radiofrequency ablation with pullback. Fine-tuning involving RF catheter type and ablation protocol was performed using ex vivo porcine models, and posteriorly, sealing effectiveness was assessed on an in vivo pig model.