Biomedical Electrical Impedance Tomography System Design And Research Based On APT

Bio-medical electrical impedance tomography (EIT), as a new measurement technology based on electromagnetic theory, can reconstruct the impedance distribution of the interested region.through reconstrution algorithms by measuring the voltage signal on the electrodes when small alternating signal applied on the electrodes placed around the surface of body According to the electrical characteristics of biological tissues and organs, the related physiological and pathological information can be extracted from the boundary(or measured) data and the reconstructed images. EIT images not only reflect the anatomical structure, more importantly, can provide a wealth of functional information. It’s a new generation of functional imaging techniques appearing in nearly30years after the form and structural imaging. The technology is prospective in the field of clinical monitoring applications because of non-invasive, non-radiation, simple structure, moderate cost and visualization.In this paper, EIT’s mathematical model of forward problem and the solving of inverse problem are researched in depth and several reconstruction algorithms are analyzedafter the instructions of EIT’s development, characteristics, application prospects and the difficulties. The contour back projection algorithm is adopted to reconstruct one object in a circular tank and the resolution of the imageis satisfied. In this paper, a data acquisition strategies based on APT working style is proposed and a16-electrode data acquisition system based on ATmegal6microcontroller is designed to meet the requirements of data measurement. The system uses direct digital synthesis (DDS) and three operational amplifier circuit voltage to construct controlled current source (VCCS),which the frequency, magnatitude and phase are all adjustable with high stability and output impedance below70MHz. Afterthe multiplication demodulation, data amplification, filtering, conversion, the collected data is transfered to computer. In this paper, the function modules composed the system is discussed and analized in detail. The results of testing shown that the system poses the features as1mV conversion accuracy and100KHz data acquisition frequency,which can meet the needs of system design.