Research Of Multi-Frequency-One-Time Exciting Measuring Signal Extracion Method For Bioelectrical Impedance Tomography System

Multi-frequency-one-time Bioelcetrical Impedance Tomography (MFOT-BEIT) is based on the principle of different tissue and organ with different impedance and sensitivity to exciting signal frequency, injecting tiny security exciting current by excitation electrodes and measuring the voltage of the tissue surface by detection electrodes at the same time. The complex impedance information of tissue or organ is calculated and reconstructed image with the measurement signal under the condition of multi-frequency-one-time excitation. MFOT-BEIT can judge the physiological and pathological state of biological tissue or organ by the image feature parameter.Now MFOT-BEIT is a hot research topic in the field of biological information detecting at home and abroad. Extracting the complex impedance information is one key technology in MFOT-BEIT, so the research has important theoretical value and application value. The production method of multi-frequency-one-time excitation signal is introduced in the thesis, and preliminary study on the impedance information extraction method is implemented as well.The main research tasks of the thesis which are based on previous studies are as follows:1. The production method of excitation signal and the impedance information extraction method about multi-frequency bioelcetrical impedance measurement system are introduced in detail at home and abroad. The measuring principle is analyzed too.2. The producing principle and the spectrum characteristics of multi-frequency one-time excitation signal based on Walsh function are analyzed. The thesis proposes an implementation method about synthesizing multi-frequency-one-time excitation signal based on the discrete Hadamard sequence of Walsh function. In theory, the method can produce a multi-frequency signal containing m (m is odd) primary harmonics. According to actual measurement requirement, the thesis realizes the output signal with a field programmable gate array (FPGA), which has seven primary harmonics.3. The impedance information extracting method based on multi-frequency-one-time exciting mode is researched preliminarily. According to the characteristic which the multi-frequency-one-time signal energy is mainly concentrated in the different primary harmonics points. Information extracting algorithm based on primary harmonics of different frequencies is proposed. The basic idea of algorithm is that the measurement signal is FFT transformed firstly, then the impedance amplitude and phase information are extracted for corresponding frequency point of the primary harmonics. The simulation results show that the proposed algorithm is feasible. 4. As to the FFT algorithm, which is used in multi-frequency-one-time complex impedance extraction, brings great measurement error due to the data non-integer-period sampling. Algorithm using FFT combined with all phase FFT(APFFT) to extract the complex impedance is introduced, and the method is applied to2R-1C model. The simulation results show that the maximum amplitude relative error is less than1.9%, and the phase absolute error is less than0.9degree. The proposed method is able to meet the requirement of the electrical impedance measuring system.