| Electrical Impedance Tomography(EIT) is a novel non-destructive tomographic functional imaging technique, which reconstruct the resistivity distribution in the case of the human body changes through excitating the injection safety excitation signal and then measuring the corresponding surface electrode potential. As a non-invasive and low-price clinical monitoring technology, EIT is expected to fill the gap in the field of clinical monitoring of dynamic changes in disease surveillance.Fourth Military Medical University EIT research team developed a set of EIT high-precision data acquisition system on the EIT research basis for many years, and carried out the clinical images EIT monitoring Detections in the international firstly. Research showed that the system can effectively monitor changes in the body resistivity imaging, which provided a strong support for the clinical diagnosis. But higher requirements to EIT system was put forward with further research work of new EIT clinical applications. On one hand, in order to perform EIT rapid detection research to distinguish different organizations better, a higher frequency impedance information need to be collected on the original bandwidth; On the other hand, the original data transmission of USB protocol often led to abnormality of EIT monitoring due to the environmental electromagnetic interference in long continuous image monitoring process, and thus further improvements were needed to the system. To solve above problems, the research work done includes the following two aspects:(1) Study on high performance current source based on the Mirroring loop circuit for EIT systemAs the core input part of EIT data acquisition system, the output accuracy within the effective band of excitation source impacted the image quality EIT system directly. The excitation source of currently EIT system adopted a voltage-controlled current source by the precision current feedback amplifier, which achieve a better output current accuracy within a certain frequency range. However, due to the limited bandwidth of the excitation source amplifier, the output impedance of the excitation source and common-mode rejection ratio decreased with the increasing frequency, which led to the problem of insufficient accuracy of the excitation source output in high frequency.In order to solve the current problems of excitation source in EIT system, a new single-ended voltage input range of excitation mirror circuit was proposed in this thesis.The simulation software comparison tests were done firstly to verify the reliability of the design, then the measurement analyses and comparisons with the other circuits of the excitation source circuits were done in this thesis. The results showed that the output impedance of the current source designed in this thesis was 600 kΩ when the excitation frequency of 500 k Hz,-3d B bandwidth up to 700 k Hz. The CMRR of EIT system constituted by the current source designed was up to more than 83 d B. Thus, the excitation source designed in this thesis possessed an excellent output accuracy and stability over a wide frequency band, which provided a high quality of excitation signal for EIT data acquisition system.(2) Study on the data transmission module of netowrk transport protocol for EIT systemAs the interaction part between the software and hardware of EIT system, data transmission module was required to have a characteristics of high-speed and stability. The data transmission module of USB interface used in current EIT system had a poor resistance to electromagnetic interference, thus led to an unstable communication reality in the course of clinical care. To solve this problem, a data transmission module which used a digital signal processing chip as the core was set up in this thesis, and an Ethernet transmission protocol EIT data acquisition system was realized. Data transmission system related performance tests showed that the designed transmission module had 9.5Mbps bandwidth, good stability and resistance to environmental electromagnetic interference, which was capable to carry out the needs of the current clinical EIT monitoring detections and other related research.In conclusion, in this thesis a new EIT excitation source and the EIT network transmission data module were proposed by analysis of the existing problems on current EIT system. An EIT data acquisition system with a higher stability network-based transmission was built on the former one. By performance comparision and evaluation experiments, the excitation source and data transmission module designed in this thesis greatly improved the performance and stability of EIT data acquisition system. The study in this thesis will help further promote EIT to the clinical monitoring applications. |
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