Digital Electrical Impedance Tomography Hardware System Design Based On FPGA

Electrical impedance tomography (EIT) as a new medical imaging technology developed in30years after morphology and structural imaging is one of the major research topics in biomedical engineering field today. EIT becomes a research hotspot quickly as an ideal and a promising noninvasive medical imaging technology due to non-radiation, non-invasive, repeatable, reusable and fast functional imaging features besides low cost and easy installation. This research is supported by the Natural Science Foundation of Tianjin Science and Technology Commission under project "Research on the key technologies of non-invasive monitoring of ventilation based on electrical impedance tomography"(Grant Number:08JCYBJC03500).In the reasearch, I designed and implemented a set of digital FPGA-based EIT hardware system, the main work presented in this paper is summarised as follows:1. Through investigation and comparison, the master-slave working pattern is determined to realize FPGA-based digital data acquisition system of biomedical electrical impedance tomography.2. Take XC3S500E-5FG320FPGA as a control core, embed a8-bit microprocessor PicoBlaze to implement functional modules, such as programmable excitation source, analog channels switching, Orthogonal sequences demodulation, data cache, serial communication module and the logic control modules.3. VHDL language is used to compile FPGA hardware configuration, Delphi software is used to develop human machine interface, realizing the real-time data storage and mapping the measured curves.4. A series of experiments are carried out on a physical tank with a diameter of30cm. Experiments are designed to test the performances of the whole hardware system. The results show the data acquisition system can work with the expected targets, which gurantee the following reconstruction research.5. According to the defectives in the system, some suggestions are put forward in the aspects of electrodes, PCB design, debugging methods and so on.The innovation of this paper is the realization of excitation source. A voltage source with adjustable phase and frequency is achived by internal DDS IP core, the signal is processed by a high-speed digital-to-analog converter and the second-order Butterworth low-pass filter, transferred by VCCS circuits, the qualified excitation current source is generated. The performances of the current source are tested and the results are presented in the paper.