A Design Of Multi-frequency Electrical Impedance Tomography Data Acquisition System

Bioelecticeal impedance tomography technique is a physical methods or means used to acquire human biomedical data from electric property and its changes of tissues and organs. it’s a new generation of functional tomography technology after the morphological and structure tomography. it has the advantages such as non-invasive,non-injury, non-ionization radiation and high-rate data acquisition,low-cost compared with traditional tomography technology. In recent years, the technology is widely used in the study of health diagnosis and diseased organs detection, and quickly become a research hotspot. But its inherent nonlinear makes the tomography accuracy low and what’s more imperfect in algorithm makes it still in the laboratory environment, there still exist some distance between this technology and its practical use. The main work scientific researchers do recent years around the issues is improving present algorithms in order to adapt to nonlinear nature and improve the precision of image acquisition as much as possible. This paper based on the participation of the project, describe and explore hardware designing, software programming and debugging related to the project, also took some measures to try to improve the inherent defects of the technology, the mainly work this paper done including following:1. The system adopts modular design, which can improve the portability and practical. Several sub modules can be design, simulate, work alone or joint work. It is convenient for system debugging and upgrading lately. Using Multi-frequency operation mode, which is more practical compared with the conventional single sweep way For the generation of multi-frequency signals, we analyzed several common methods of multi-frequency signal generation, such as sweeping, digital synthesis, direct digital synthesis, and finally selected the direct digital synthesis(DDS) manner to produce multi-frequency signals. Adopting 16 electrodes for signal excitation with adjacent or relative mode, can apply to a variety of tomography algorithm.2. Prompted the original system, improve the imaging speed and imaging quality. Such as using multi-frequency signal source improved the traditional single frequency electrical impedance tomography equipment, adopting the method of direct digital synthesis modified constant current source module. Increased the accuracy and flexibility compared with the traditional way.other improvement approaches like selectable electrode incentive mode etc. Using multiple electrode sampling data parallelly, and by choosing a more appropriate system architecture to realize acquisition image speed boost.3. The paper analyzed Cole-Cole model and other electrical impedance characteristics that related to electrical impedance imaging technology.Compare and analyse the advantages and disadvantages of several commonly used embedded chipsuch as MCU, ARM, DSP, FPGA.Finally decided to adopt the combination of FPGA(Field Programmable Gate Array) and ARM(Advanced RISC Machines) scheme designed system architecture,which can make the system flexible in processing and can be easily customized.Using Verilog language which is concise and easy to understand, it’s facilitate to learn and transplantation for follow-up personnel.