Influential Factors And Application Research On Dielectric Properties Measurement Of Human Tissues Based On Open-Ended Coaxial Probe Method

The dielectric properties of biological tissue are the inherent property of biological tissue when loaded in the electromagnetic field.The change of dielectric properties of biological tissue can reflect some physiological and pathological changes of the tissue.It is reported in the literature that the dielectric properties of malignant and normal tissues are usually different,which provides a theoretical basis for related clinical applications and basic research.The study of the dielectric properties of human normal and malignant tissues is indispensable for the development of tumor tissue diagnosis and treatment techniques.The accurate and reliable acquisition of tissue dielectric properties requires understanding of some relevant influencing factors in the measurement process.The open-ended coaxial probe method is a fast,non-destructive method for measuring the dielectric properties of tissues.However,the open-ended coaxial probe method in the practical application of dielectric properties measurement,there are still many factors that interfere with the measurement results,therefore,carrying out the exploration of these factors is very necessary.In the study of the measurement method of the dielectric characteristics of the open-ended coaxial probe method,the influence of the output power on the measurement error of the dielectric characteristics,and the depth of the probe detection and the influence of the pressure applied to the object to be measured on the measurement result of the dielectric property are all explored.Simulation system for an open-ended coaxial probe with an outer diameter of 3.58mm and 2.2mm,a characteristic impedance of 50 ohms is established using the XFDTD electromagnetic simulation software,and in the-50dBm～30dBm power range,50MHz-4GHz frequency range of the dielectric characteristics of the measurement error and power,the relationship between the probe depth and power were simulated.At the same time in the 50 MHz-500 MHz frequency band,-50dBm-15dBm power range using the network analyzer Aglient4395 measured experiment;In addition,the effect of the pressure exerted by the probe on the object to be measured is analyzed by two phantom modes.The simulation results show that the measurement error of dielectric properties is basically unaffected by power,and the measured results show that the output power should be greater than-10dBm to ensure that the measurement error is small;The simulation results of the 3.58mm probe detection depth show that the probe detection depth is 2mm in the-50dBm～30dBm power range,The simulation results of the 2.2mm probe detection depth show that the probe detection depth is0.5mm-1.0mm in the-50dBm～30dBm power range,The measured results show that the power is less than-30dBm is very unstable,the power is greater than-10dBm,the probe depth is also about 2mm at different power for 3.58mm probe and the probe depth is also about 1.5mm at different power for 2.2mm probe,and the power of the probe depth has little effect;The measurement results of pressure vs.dielectric characteristics show that the dielectric characteristics increase with pressure,and after a certain threshold value is exceeded,the measurement results basically do not change with pressure,and the pressure threshold is related to the phantom to be measured.The above-mentioned factors for the study of the measurement of biological properties of tissue have a guiding role.In the clinical measurement of the dielectric properties of human tissues,To investigate the difference of dielectric properties between the mucosal surface and serosal surface of malignant tissue,the adjacent tissues of 1cm,3cm and the mucosal surface and serosal surface of normal tissue for the colorectal tissue.The dielectric properties of the mucosal and serosal surface,adjacent tissues of 1cm,3cm and normal mucosal and serosal surfaces from 39 colorectal cancer patients were measured by Network Analyzer AV3656A in the frequency range of 50MHz-3GHz,and the corresponding difference of dielectric properties was analyzed respectively.The results showed that the dielectric properties of malignant mucosa surface were higher than that of adjacent tissues of 1cm,3cm and normal mucosa and had significant difference(P<0.01);The dielectric properties of adjacent tissues of 1 cm,3 cm and normal mucosa surface decreased in sequence;In addition,the dielectric properties were significant difference(P<0.01)between the mucosal and serosal surface of malignant tissue at 64MHz,128MHz,298MHz,433MHz,915Mhz,and no difference(P>0.01)at 2.45GHz;The dielectric properties of mucosal and serosal surface of normal tissue were no significant difference(P>0.01).The results of this study are expected to achieve intraoperative marginal detection and evaluation of colorectal malignant tissue by tissue dielectric properties,which has important clinical value.In addition,the results of this research have a fundamental role in the development of magnetic resonance tomography and thermal ablation of tumors.