| The brain is the nerve center of human being and its metabolism is very active. The blood volume the brain needed is about 15-20% of the cardiac output. The brain consumes up to 25% of the whole oxygen the body needed. The neural function would be harmed if the ischemia or the anoxia occurred, for the brain can not store energy. It has been demonstrated that the ischemia and the anoxia are the chief factors to human health. So the earlier diagnose of brain disease is very useful. Electrical impedance tomography (EIT) is a new medical imaging modality which is noninvasive, low cost, and able to get functional image. By imposing harmless drive currents on the body surface and measuring the responded voltage on the body surface, the relationship of driven and responded signal was developed by using reconstruction algorithm, from which the distribution of impedance or its variation can be delivered. By imaging the brain function changes with EIT, the focus of ischemia, haemorrhage and tumor may be located in time. However, the relationship between the impedance of brain and its ischemia is not clear, and the electrical impedance characteristics of brain tissues have not been reported as well. The electrical impedance characteristics and its parameter of brain, the resistivity for example, are of particular relevance to localize a focus of activity. On the other hand, because the skull has a higher resistance, this lead to much of the applied current pass directly between electrodes in the scalp instead of entering the brain, the signal resulted from the changes in the brain is substantially attenuated, and decrease the sensitivity to the central resistance change. Thus researching on the impedance characteristics is very important. This paper mainly concerned about the basic research of electrical impedance characteristics of brain. The in vivo measurement and EIT imaging based on 1 6-electrode were performed on the rabbit. The cerebral ischemia model was made by ligating common carotid arteiy. The in vitro measurement include the samples of rabbit brain, human brain and skull. We use the Solartron 1 255B frequency response analyzer and apply the two- or four-electrode measurement methods. The frequency range of measurement is 1Hz to 1MHz. The main contents of research I .Both in vivo and in vitro measurement of rabbit brain tissue's complex impedance are made under both normal and ischemia conditions by using two- and four-electrode measurement methods in the frequency ranged from 1Hz to 1MHz. 2.The dynamic images resulted from the resistivity changes of rabbit cerebral ischemia are reconstructed based on 16- electrode MT system. 3.The in vitro measurements of human skull's impedance spectra are made. The impedance frequency response curves of human skull with different anatomic structures are compared. 4.The in vitro measurements of human brain tissue's complex impedance are made by using four- electrode measurement methods in the frequencies ranged from 1Hz to 1MHz. The main results and conclusions: I .The results of in vivo measurements showed that after ischemia the whole rabbit brain impedance increased up to 75% at frequencies lower than 10Hz. In the frequency ranged from 1kHz to IMI-Iz, after ischemia it increased up to 15% and matain a constant value. This suggested that it is feasible to image the cerebral ischemia with EIT method. 2.The results of in vitro measurements showed that the resistiv...
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