Law of diffusion bubbles produced by high-voltage pulsed electric field in liquid

Abstract

Pulsed Electric Fields (PEFs) is a novel physical energy source for the treatment of atrial fibrillation and tumor ablation, which has advantages over traditional thermal ablation, such as non-thermal, short treatment time, tissue selectivity, and low contact pressure requirements. The diffusion bubbles generated during physical ablation may lead to gas embolism and silent cerebral events(SCE), with potential hazards such as tissue damage and cerebral ischemia. Previous studies have shown that the amount of bubbles generation is correlated with the electrical properties of the treated object, pulse parameters (pulse waveform, treatment time and input energy), and electrodes. The amount of bubbles are more significant at the cathode than at the anode, and the amount of bubbles positively correlates with the input energy. However, to the best of our knowledge, no studies have been conducted to investigate the impact of ablation pulse parameters on diffusion bubbles. Therefore, in our experiment, a platform for pulse generation and diffusion bubble observation was built, and the needle-ring electrode we made realized the capture and measurement of diffusion bubbles. Since pulses with voltage within 3kV and pulse width within 100µs are commonly used as ablation parameters for atrial fibrillation and tumor in Pulsed Field Ablation (PFA), the pulse widths of unipolar pulses were selected as 5µs, 10µs, 50µs, and 100µs, and the number of pulses applied is 1. The pulse voltage was determined according to the parameters commonly used in PFA and the simulation calculation of the field strength distribution of the needlering electrode. After determining the parameters, this experiment explicitly investigated the relationship between diffusion bubbles and solution conductivity, pulse voltage, pulse width, input energy, and other parameters. Meanwhile, the size distribution of diffusion bubbles under different operating conditions was statistically investigated. Besides, the possible causes of diffuse bubbles were also explored. We evaluate the amount of bubbles by measuring the cross-sectional area of the diffusion bubbles from a top-down perspective. The experimental results showed that:the area of diffusion bubbles generated in the liquid is positively correlated with pulse voltage and input energy; high conductivity and long pulse width can enhance the thermal effect and increase the area of diffusion bubbles; diffusion bubbles with a diameter size larger than 100 μm are easily generated under high conductivity and high pulse width conditions. By speculating on the results, the electrolytic reaction may be the main source of diffusion bubbles when the needle electrode is the cathode. This study is expected to optimize future pulsed electric field ablation parameters.