Basic Research On The System Of Multi-frequency And Electrical Impedance Parametric Tomography

This dissertation centers on the system of muli-frequency and electrical impedance parametric tomography. Theory predictions, Cole-Cole model, strategy of muli-frequency data acquisition, influencing factors on image reconstruction, method of electrical impedance parametric tomography are studied respectively. The main contents of the thesis are as follows:1. The principle and algorithm of EIT are introduced. A discussion is put forward that the method of the single frequency EIT is not conformable for directly transplant to EIPT since the frequency characteristic parameters of the impedance is neglected in the theoretically model. However, the problem is too complicated to solve if the frequency characteristic is taken into account. These theory predictions restrict the perfect description of EIPT come into being.2. Nonlinear transform relationship between the conductance and capacitivity of the bioelectrical impedance is demonstrated, and the relation between them when different dispersion factors exist in the Cole-Cole model is presented in addition. The connection of the Cole-Cole model parameters to the ohm resistance and capactive reactance of biologic tissue is analyzed, and validation experiment is conducted. A strategy of muli-frequency data acquisition avoiding of high precision measurement of reactance within wide frequency range is advanced as well as the corresponding parse method for the Cole-Cole model parameters is brought forward.3. The muli-frequency data acquisition system and the algorithm of data demodulation are introduced. MMX technology is introduced to the demodulation of muli-frequency data acquisition system and data demodulation is accelerated in the test.4. Influencing factors on image reconstruction are analyzed. The effects of the electrode polarization and the electrode frequency characteristics on reconstructed image are simulated and validation experiments are devised as well. A pretreating method for muli-frequency data is proposed. The preliminary experiment result shows the effect of the electrode frequency characteristics is reduced. It is also found in theoretical analysis that the method is helpful to release the influence of the excitation source output swing on the reconstruction data.5. An EIPT reconstruction method for muli-frequency system with fewer frequencies is described. The algorithm for the tomography of the partial Cole-Cole model parameters with a 4-frequecnies system is depicted. Reconstruction result with good location and shape is yielded utilizing the data acquired from a phantom. The working frequencies suitable for EIPT of main human organs are reckoned.