Open Three-dimensional Multi-frequency Impedance Measurement System

Breast disease is a common disease of women. With the continuing increase in incidence of breast cancer, it has become a major threat against women's health. Because the pathogenesis of breast cancer is not clear, early detection and timely treatment is the key to reducing mortality. Generally speaking, the beginning of disease is functional failure, then is morphological changes. Common medical imaging techniques can only detect morphological changes, but functional medical imaging technology can detect functional failure.Electrical impedance tomography(EIT) is a functional medical imaging technology in recent years. It injects a safe electric excitation and measures the electrical response by electrodes around the skin, to reconstruct the conductivity distribution within the body. The advantages of EIT include: noninvasive, inexpensive, and so on. But because of limited information and ill-conditioned algorithm, the resolution of EIT is restricted. EIT is considered to be an adjunct to early disease detection and continuous monitoring method.In this paper, a open three-dimensional multi-frequency impedance measurement system is studied to detect human breast disease. It analyses breast tissue under electric excitation at different frequencies and the mathematical model of EIT, designs EIT measurement system and built experimental platform to measure the parameters of this system. Mainly to do the following:(1)It analyzed lesion tissue with different electrical characteristics of normal tissue, Specific to normal breast tissue and cancerous tissue under electric excitation at different frequencies. And the mathematical model of EIT was deduced.(2)To enlarge the limited information of two-dimensional EIT, it designed three-dimensional EIT of 64 electrodes. 8*8 electrode array was designed for breast, and a complex back electrode was selected by use of discrimination norm. Four-electrode measurement was chose.(3)It used two kinds of incentives: sweeping method and mixing method. Two methods were based on direct digital frequency synthesis, by use of field programmable gate array.(4)To demodulate signal, it studied two demodulations: digital phase sensitivity detection and fast Fourier transform. (5)It designed circuits to measure the current source's output current, impedance and output voltage. It also studied the power supply module, communication module.(6)It measured the current source's impedance and the spectrum of mixing frequency. Set a resist network as the load, to get relative precision of the system. By use of agar, a experiment is finished, and preliminary imaging result was obtained.