Design Of Improved Excitation Source And The Conductivity, Permittivity Detection Of Brain Edema

Brain magnetic induction tomography is a new non-contact imaging technology with the theory of magnetic induction detection. This technology detects the conductivity distribution of bio-tissues which will be used for image reconstruction. Because of the noninvasive and contactless advantages, it will be used to clinical monitoring for the patients with brain edema.It is very common in clinic that cerebral edema arise from many reasons, such as high blood pressure, brain tumors, brain traumatic injury and so on. In order to diagnose and treat these patients in due course, doctors need some medical instrument with the features of real-time and accurate imaging. The BMIT have obvious advantages and potential application prospect, but some patients'body will get damage due to the excessive and exposure to magnetic fields. Meanwhile, we can't find more details about the security of patients in exposure to magnetic fields in some studies. So the excitation source with secure standards will be significant in the clinical application. At the same time, the conductivity and permittivity of cerebral edema are also important for realization of BMIT in clinic. So we should detect the spectrum of conductivity and permittivity of edematous brain tissue and normal brain tissue. These data will be used as a reference not only to the theoretical model but also to the phase shift detection of BMIT system.In this study, we designed and realized the excitation source with secure standards which could produce magnetic field within the secure standards. We also detected the conductivity and permittivity of edematous brain tissue and normal brain tissue.The main work of the research is as follows:1. We had designed three kinds of coils in accordance with I IEEE Std C95.1 of exposure to magnetic fields. There were circular focusing coil, rectangular focusing coil and solenoid;2. We measured the inductance of three kinds of coils and adjusted the exciting current on the base of whole flux. We used Faraday's law of electromagnetic induction to measure magnetic field which must meet the requirement of IEEE Std C95.1.3. Two kinds of saline solution with the conductivity of 0.5S/m and 1.5S/m were measured with safety excitation source in BMIT system. The phase shift result showed that this excitation source can be used in BMIT system, and detect phase shift effectively with IEEE Std C95.1.4. We used rabbits with occluding lymphatic drainage to make the model of LCE. After several days, the edematous brain tissue and normal brain tissue were be measured. The conductivity and permittivity were obtained. They were the function of frequency which were called spectrum. Research results showed that:1. The improved excitation source which was designed and realized with IEEE Std C95.1 could produce magnetic field in accordance with this standards. For example, the magnetic induction intensity produced by circular focusing coil was 0.189T, 0.057T and 0.0054T at three frequencies respectively. They were met the requirements of standards. The other two kinds of coils also produced magnetic fields with IEEE Std C95.1.2. In the saline solution experiments, there were significant differences of phase shift between two kinds of models with the standards. It showed that the phase shift produced by saline with high conductivity was greater than that by saline with low conductivity, while at the same saline the phase shift produced by high frequency was greater than that by low frequency.3. The conductivity and permittivity of brain tissue changed when brain edema happened. The conductivity of edematous brain tissue was higher than that of normal brain tissue, but the permittivity was opposite.In this study we designed and realized the new type of excitation source with safety standards. At the same time we used a TCXO to decrease the bulk of whole system and increase the convenience of BMIT system.In the brain tissue experiments, the result showed that the conductivity of edematous brain tissue was higher than that of normal brain tissue, but the permittivity was opposite. The phase shift produced by edematous brain tissue was greater than that by normal brain tissue. This result of the brain will give us a basis in the brain tissue BMIT experiments and help us to calculate the academic phase shift in theoretical BMIT model.