Study On In Vivo Measurement Of Tissue Electrical Properties Based On Parallel Plate Capacitance Method

Biological tissue has its specific electrical characteristics,which is related to many factors,such as water content,temperature,blood flow richness,cell type,density,cell membrane structure and so on.Changes in the physiological or pathological state of the tissue will lead to changes in these factors,that is,changes in the electrical properties of the tissue.On the other hand,if the electrical characteristics of the tissue have changed,it indicates that the physiological or pathological state of the tissue has changed.Therefore,the measurement of electrical properties of biological tissue is helpful to the screening of early cancer and provides a promising treatment for clinical diagnosis of early cancer.At the same time,understanding the electrical characteristics of biological tissue also provides surgical guidance for clinical operations such as radiofrequency ablation.In this paper,based on the impedance analysis of parallel plate capacitance,a new type of lead parallel plate capacitor is designed and fabricated,and a set of measurement system of electrical properties(conductivity and permittivity)of imitating body and tissue(conductivity and permittivity)is built.The electrical characteristics of biomimetic,in vitro tissue and mouse liver tumor tissue are measured and analyzed in the range of 0.5 MHz-10 MHz.First of all,the spacing,thickness and radius of the designed capacitor plates are simulated by COMSOL Multiphysics simulation software,and the optimal size is obtained through the additional capacitance generated.Secondly,based on the theory of suppressing the edge effect of capacitors,a new type of lead parallel plate capacitor is designed,and the electric field distribution and potential isoline between plates are simulated,and compared with the existing capacitors,it is proved that the lead capacitor is feasible.Thirdly,the lead capacitor is made according to the simulation results,and the capacitor is calibrated with 0.010.07mol/L Na Cl standard liquid,and the error between the standard value and the measured value is analyzed.Finally,the electrical properties of biomimetic,isolated pork tissue and mouse liver tumor tissue at 0.5MHz-10 MHz frequency were measured using lead capacitor.The differences of electrical characteristics with frequency between isolated adipose tissue and muscle tissue of pig,muscle tissue with high blood content and muscle tissue with low blood volume,and the trend of electrical characteristics with frequency during the growth of mouse liver tumor tissue were analyzed.The results show that:(1)in the frequency range of 0.5MHz-10 MHz,the electrical properties of Na Cl solution,biomimetic,in vitro and in vivo tissues all follow a law,that is,with the increase of measurement frequency,the electrical conductivity increases and the dielectric constant decreases.(2)the electrical property of porcine muscle tissue in vitro is higher than that of adipose tissue,and the electrical property of muscle tissue with high blood volume is higher than that of muscle tissue with low blood volume.(3)with the continuous growth of mouse liver tumor,its electrical characteristic value is higher at the corresponding frequency.The conductivity of liver tumor in its frequency band is 0.2401-0.614,which is 1.62 times that of normal liver tissue in low frequency band,1.15 times in medium frequency band and 1.94 times higher than that in high frequency band,and the permittivity in its frequency band is 546.3-3545.It is 1.28 times that of normal liver tissue in low frequency band,1.08 times in medium frequency band and 2.44 times higher than that in high frequency band.The values of electrical characteristics measured by the experiment fall within the data in the literature,which not only reflects the accuracy of the measurement of parallel plate capacitors,but also provides a data basis for judging the benign and malignant of the tissue.(4)two reference coefficients y0 and A were obtained by fitting and analyzing the electrical characteristic curve of mouse liver tumor,which can be used as a reference to assist diagnosis in the analysis of benign and malignant tumors.