Research Of Three-dimensional Electrical Impedance System In Breathing Process

Electrical impedance tomography(EIT:Electrical Impedance Tomography)technology is a non-invasive imaging technology to obtain internal images of the body,which is based on different tissues in vivo or in the same organization with different physiological and pathological conditions have different conductivity characteristic.Through exert a safe point current(voltage)on the living body surface and measure the surface voltage at the same time,according to the electrical tomography image reconstruction algorithm to reconstruct the electrical impedance distribution images of the inside of the measured organism by a computer.It is intuitionistic showing up the biological impedance distribution and the change of body's tissues or organs in 2D/3D graphics for diagnosing and evaluating tissue or organs provide basis.EIT technology has received much concern in the medical imaging techniques field with its non-invasive,non-radiation safety,low cost,fast imaging,continuous measurement and real-time visualization,etc.This paper started from physical model of EIT Technology,and in-depth study of Measurement Mechanism about three-dimensional EIT systems.We designed and constructed the system hardware included signal source module,data acquisition module,FPGA control module,etc,and wrote a complete set of system application by use of VHDL.We achieved a two-dimensional and three-dimensional static and dynamic electrical impedance tomography in the test tank,which verified the system reliability and stability.Finally,we achieved an electrical impedance tomography of pulmonary respiration procession in the human chest and obtain a favorable effect.The main research works are as follows:1.Designed a set of 32 electrodes electrical impedance imaging hardware system with high precision.The system use PC as the primary controller,and use Lab VIEW language to write PC software which includes sending commands and processing upload data,and invoke MATLAB to image.Moreover,the system used FPGA as a slave controller including generating an excitation signal,switching electrode channels,selecting programmable gain amplifier,acquisition and processing of data,the data was collected through a serial port communication with PC.The experimental results show that the system measurement accuracy is up to 0.082%,the SNR is up to 60.3dB,spatial resolution is up to 0.29%.2.A problem is analyzed related to quadrature sequences digital demodulation algorithm due to frequency difference exists between reference signal and measured signal which can cause inaccuracy of data and sacrifice the image quality.An approach solving the problem is proposed based on extracting impedance amplitude directly by multiple tomography(EIT).The theory and experimental results verified the feasibility of extracting impedance amplitude directly.The accuracy and stability of the system are increased and the image quality is improved.3.Two-dimensional imaging simulation experiment was carried out on the EIT system.A two-dimensional system model is constructed by COMSOL.Using MATLAB to deal with data based on conjugate gradient algorithm and achieve the two-dimensional static and dynamic imaging.Imaging result clearly showed the number,shape,size,position,motion state and other information of the target object in the test tank.4.Achieved a two-dimensional dynamic imaging of pulmonary respiration process on the human body.A two-dimensional lung simulation model with prior information is constructed by COMSOL,and calculate the sensitivity matrix by MATLAB.Data collection in the Volunteers chest is carried out and by use of conjugate gradient algorithm,we obtain a good quality two-dimensional image.5.Three-dimensional electrical impedance imaging experiments is conducted on the test tank.Using COMSOL build three-dimensional simulation model of tank,using quasi diagonal incentives and adjacent measurement working mode and calculate the new sensitivity matrix by MATLAB.Three-dimensional data acquisition and static and dynamic imaging was carried out on upper and lower level electrodes of the test tank sink.Imaging results accurately reflect the number,shape,size,position,motion,height and other information of the target object in the test tank.6.Three-dimensional electrical impedance data acquisition experiments during human respiratory process.Pasted a total of 32 ECG electrodes in two layers in the chest outside of the volunteers,using quasi diagonal incentives and adjacent measurement working mode,collecting boundary voltage during respiratory process and the breathing process data are analyzed.This system provide an effective solution for the improvement and perfection of the EIT system and further study on evaluation of pulmonary function and bedside respiratory monitoring requirements and help doctors make the correct diagnosis.Finally,the paper also puts forward some improvement suggestions on the basis of summarizing the research.