Experimental teaching research on the dynamic changes in tissue impedance after treatment by pulsed electric field
[Objective]Electroporation has been widely used in biomedical applications,which is a typical medical-engineering cross-field.Currently,in the application of irreversible electroporation,the assessment of the ablation outcome in real time by medical imaging methods has become an issue.To solve this problem from the engineering field and create a teaching program for students in related majors,this study describes in detail how to build the electroporation platform and measure the ablation results and tissue impedance.The characteristics of the impedance variation are extracted by the equivalent circuit model.Finally,the correlation between the ablation outcome and the impedance change is discussed,which might be the new method to assess the ablation outcome in real-time.[Methods]This study investigated the tissue impedance changes and the ablation outcome induced by high-voltage pulsed electric fields.The pulsed voltage and current waveforms were recorded by an oscilloscope and used to analyze the electroporation process.The tissue impedance change induced by different pulse amplitudes was measured by an impedance analyzer,and the load characteristics were analyzed based on the impedance spectrum.To extract the characteristics of impedance change during treatment,the equivalent circuit model of tissue was proposed according to the features of the tissue structure.The measured impedance data were fitted to the circuit model to determine the value of every element in the circuit.The potato tube,which is the commonly used tissue model in irreversible electroporation,was used to detect the ablation outcome for different pulse parameters.The ablation outcome was quantified by the length and area of the ablated zone.[Results]The experimental results of the response current showed that:(1)At the first pulse,the increase in the current during pulse on time caused by electroporation could be easily identified.(2)As more pulses were applied,the current change during the pulse seemed to be saturated,indicating the saturation of electroporation.The measured impedance and the equivalent circuit model yielded the following results:(1)The impedance of the tissue started from the capacitive load,reflecting the polarization process between electrode and tissue.(2)As the frequency increased,the impedance could reflect the resistive characteristics of the extracellular fluid,the capacitive characteristics of the cell membrane,and the resistive characteristics of the intracellular fluid in sequence.(3)The circuit model could fit the impedance spectrum well,and the variation of the element value caused by the pulsed electric field could be explained by tissue electroporation.(4)The changing trends of the extracellular and cell membrane parameters were consistent with the ablation outcome,which had the potential to be used to assess the irreversible electroporation outcome in real-time.[Conclusions]By investigating the electrical and biomedical changes in the tissue after treatment by pulsed electric fields,the changes in the response current and impedance spectra are measured and correlated with the electroporation process.The equivalent circuit model can describe the tissue property well,and the changes in the extracellular resistance and cell membrane impedance are consistent with the ablation results.This study provides the potential electrical indicators to evaluate the ablation outcomes of irreversible electroporation in real-time.This teaching program helps students understand the connections between medicine and engineering,enhancing their skills in the application of theoretical knowledge in electrical engineering.
pulsed electric fieldirreversible electroporationimpedancetissue ablationinterdisciplinary field of medical and engineering
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