Theoretical Calculation And Experimental Detection Of Phase Shift In Our Single-channel BMIT

BMIT is a potential imaging technique based on the principle of magnetic induction to detect conductivity distribution of biological tissues in brain, which is a frontier research in this field at present. This technique has many merits such as non-invasive, non-contact, miniature and continuous, for observing patients with brain edema in clinic. BMIT is an imaging technique mainly based on the principle of eddy current. When the excitation magnetic field across a target, the alternating magnetic field generates eddy currents in the target, any change in the conductivity distribution creates a change in the induced eddy currents, these eddy currents generate a secondary magnetic field which is picked up by the detection coil. Then we get a set of phase shift values that are proportional to the conductivity of the target and use imaging algorithm to carry out imaging of the target.In clinic, cerebral edema arise from ischemia, hemorrhage, tumors, et al, is common, which needs to be monitored continuously and accurately for diagnosis and treatment timely. Similarly, the electrical characteristics of the cerebral edema tissue, such as conductivity and permittivity, are of great significance to implementing BMIT technique. Therefore, the conductivity spectrum of edema neuron cell model and normal neuron cell model can verify the results of phase shift measurement, as well as can provide theoretical guidance for further brain magnetic induction tomography.In this study, we established mathematical model which is based on our experimental platform. Phase shift and conductivity of agar models and SD rat neuron cell models were detected, respectively. The contents of our study are as follows:1. According to our system, a mathematical model was established for the theoretical calculation. Its analytical formulas of phase shift were developed when an object was located near the detection coil. It can provide theoretical guidance for actual detection.2. Experimental results were obtained from agar models with conductivities ranging from 0S/m to 2S/m. The results were compared with that of theoretical calculation.3. Normal neuron cell model and edema neuron cell model were made from fetuses of SD rats by neuron cultures. We detected the difference of phase shift between normal neuron cell model and edema neuron cell model. The results were compared with that of the control group model. It can verify the feasibility of detecting the phase shift on neuron cell models. It also can lay a good foundation for actual detection.4. We detected the conductivity of neuron cell models. Conductivity spectrum of normal neuron cell model and edema neuron cell model were measured. The difference of conductivity were compared between the two types of neuron cell models, as well as the neuron cell model and the control group model , to verify the results of phase shift detection.Research results showed that:1. The results of theoretical calculation: There was good agreement between the analytical and the experimental results. The phase shift increased with conductivity and volume of the targets.2. The results of phase shift detection: The phase shift of the edema neuron cell model was 0.489±0.0173o. The phase shift of the normal neuron cell model was 0.421±0.0185o. The phase shift of the control group model was 0.382±0.0132o. There were significant differences among those three models. It showed that the phase shift produced by edema neuron cell model was greater than that by normal neuron cell model.3. The results of conductivity detection: There were significant differences among three models. The conductivity produced by the edema neuron cell model was greater than that by the normal neuron cell model and the control group model. The conductivity produced by the normal neuron cell model was greater than that by the control group model.This study not only realized the comparison between the results of theoretical calculation and the results of phase shift detection, but also the conductivity spectrum produced by neuron cell models were detected. The results of phase shift detection were verified. So we can draw a conclusion that the phase shift produced by edema neuron cell model was greater than that by normal neuron cell model. We studied the cerebral edema on the level of cell. These may be of great help for further brain magnetic induction tomography.