Study Of Software Phase Detection Platform And Data Acquisition In MIT System

Magnetic Induction Tomography (MIT) uses the theory of electrical magnetic field to measure the distribution of biological tissue's electrical conductivity. As a non-invasive, contactless, miniature and continuous method, it is very important in monitoring and diagnosing the encephalic pathological changes.MIT mainly based on the theory of the eddy current. As the phase deviation has a linear relationship with the conductivity of biological tissue, the accurate detection of phase deviation will affect the imaging quality. The establishment of high-precision phase deviation detection unit plays an important role in improving the performance of MIT system.Now, most of MIT research groups mainly focus on designing hardware circuit or using down-frequency techniques to improve the precision of phase detecting unit. The precision is difficult to be improved for drift, noise and interference signals existing in the hardware circuit. The methods of software phase detecting, which mainly focus on algorithms and overcome the flaws in hardware techniques, make the detecting results more accurate.The thesis based on former researches of our group, aiming at improving the precision of phase detecting unit and reducing the interference signals, do a further research and design of phase detecting unit in MIT system with software methods. The software phase detecting platform was built using frequency spectrum analysis method, correlation method and phase sensitive detecting method. It can carry on real-time detecting of phase deviation.The main contents of this thesis are as follows:1. We analyzed the existing phase detecting algorithms and found frequency spectrum analysis algorithm, correlation algorithm and phase sensitive detecting algorithm were suitable for our system. We studied the theory of the algorithms and the influencing factors.2. We achieved the phase detecting algorithms and built software phase detecting platform with LabVIEW.3. We compared the software phase detecting methods with hardware phase detecting method by simulating experiments. We used evaluation indicators error and linearity to evaluate the software and hardware phase detecting methods.4. We detected the phase deviation of NaCl solution model, agar-NaCl model and cell model using the built software phase detecting platform and evaluated the results we detected.5. We built 16-channel data acquisition system.Finally, we established a whole software phase detecting platform with signal acquisition and processing. The phase accuracy of the software platform could be achieved at 0.01°, which was higher than the high-precision lock-in amplifier SR844 with phase accuracy of 0.02°. The paper laid a good foundation for further detecting of the encephalic pathological changes. These might be of great help for further cerebral edema-detecting work.