The Control System Design Of Three-Dimensional Impedance Measurement For Gastric Motility

Gastrointestinal disease is a common disease,usually accompanied by abnormal gastric motility.The gastric motility could be detected by functional medical imaging,which plays a monitoring role in the course of disease treatment.In this study,a three-dimensional detection and control system of gastric impedance is established based on the bioelectric impedance technique.The system uses multi-layer electrodes to explore more abundant gastric impedance information.The difficulty lies in simplifying the system and improving data collection.The main contents of this paper are as follows:(1)The basic electrical characteristics of the biological tissue are obtained by analyzing the equivalent model of the biological tissue.The relationship between the frequency of excitation signal and the impedance are analyzed based on the impedance characteristic experiment of isolated gastric tissue in 10KHz~1MHz frequency band.The two-dimensional tomography is hampered by a lack of information.Hence a three-dimensional impedance detection system with 48 electrodes is designed based on the theory of electrical impedance imaging and the characteristics of gastric motility.The system is mainly consist of electrode gating module,signal pre-processing module and demodulation module for impedance information.(2)In order to improve the system collection efficiency,the gated model of multilayer electrode is optimized firstly.Then an adaptive electrode gating model on the basis of frequency conversion is proposed.The system rationality is improved by making full use valid measuring electrodes and excluding the invalid electrodes.In the process of adjacent acquisition,the valid electrode is selected from the effective electrode matrix and at least 4.5%of the electrode strobe of the system can be reduced.Thereby,it reduces the dimension of the Jacobian matrix in the reconstruction algorithm,suppressing the time complexity of algorithm,and ill-conditioning of inverse problem.Secondly,the AD8302 amplitude and phase detector is used to reduce the complexity of the analog impedance demodulation in the hardware circuit,and improve the anti-interference of module to the surrounding high-frequency signals.As for the blurred polarity of the chip phase detection,the phase information between signals is obtained by the multi-reference signal gating and phase comparison algorithm.(3)By designing the signal gating module experiment,the relative error of the gating module accuracy is(-0.0055,0.0122),and the one-way analysis of variance(ANOVA)is used to prove that the gating module is insensitive to the signal frequency and the excitation electrode position.In the experiment of impedance demodulation module,the complex impedance of the experimental circuit is detected under different excitation signal frequency.The maximum amplitude error and the maximum phase error of this module is 3.41dB and 6.86~?respectively.Finally,the gastric impedance simulation experiment and the reconstructed image of the cylindrical agar model are provided in this study.In this study,we optimized the electrode gating model and impedance demodulation module of the system and analyzed the key modules of the system.The stability and effectiveness of the three-dimensional detection system for gastric impedance signal have been proved,which contributed to the development of gastric motility testing technology.