The Research Of Phase Detection Unit And Experiment Of Neuron Cells In MIT System

Magnetic Induction Tomography (MIT) is a potential imaging technique, which is non-invasive, contactless, miniature and continuous, for observing patients with brain edema all the time in clinic. MIT is also useful for the wounded to be treated when wars happen in a battle field, because of its miniature. The aim of the research is to implement a high-precision detection unit for phase changes in MIT and to make some basal study on brain edema.MIT is an imaging technique based on the measurement of the perturbation in the high-frequency magnetic field produced by eddy and excitation currents in the bio-tissues exposed to the field. And the perturbation is mapped onto the phase change between the signal from the bio-tissues and reference signal. The conductivity of the bio-tissues can be got to be imaged from a set of those phase changes measured. The phase change is a key parameter in MIT because it is linear with the conductivity of object. To construct a high-precision measurement unit for the phase change is a important part of MIT system.Brain edema resulted from bleeding and so on often happens in clinic, which is needed to monitor continuously. The electronic parameter of brain edema is meaningful to implementing MIT technique.In this paper, a high-precision unit for detecting phase changes is designed and implemented at the frequencies of 200kHz, 1MHz and 10MHz. And an experiment of edema neuron cell models from SD rat cortex is made using the unit. Main contents are listed as follows:1. Circuit for detecting and processing signal. The circuit consists of a sensing coil, a low-noise amplifier and a narrow-band filter, which is used to detect signal, to amplify the small signal and to eliminate the noise unwanted. The circuit designed has a maximal gain of 61.1dB and a minimal bandwidth of 1.5kHz. The three kinds of circuits are all shelled in a box made of metal.2. High-precision detection for phase changes. RF Lock-in Amplifier SR844 is used to detect the phase changes between the detected signal and reference signal. The resolution of phase-change detection is up to 0.02 degree, higher than our old-time resolution by two orders.3. An experiment of iron block and NaCl solution. The experiment is made firstly to test the performance of detection channel composed of excitation unit and detection unit. The result is that the 200kHz detection unit can detect the phase changes produced by iron block with different sizes, and that the high-frequency unit can detect the phase changes produced by NaCl solution with different conductivity.4. Neuron cell models. Normal neuron cell model and edema neuron cell model are made from fetuses of SD rats by neuron cultures. The two models have the bulk of 160mL and the density of 5.5-6×10~5cells/mL.5. Neuron cells experiment. The phase change produced by edema neuron cell model is detected, contrasting with that of normal neuron cell model, by different excitation coils and different positions of coils.The results of experiments are as follows: (1) The detection unit at 1MHz and the one at 10MHz both can detect the phase changes produced by neuron cell models from rat's cortex. (2) The phase changes produced by edema neuron cell model are smaller than those produced by normal neuron cell model. (3) The maximum of phase changes detected by the system is 0.86 degree. And the maximal phase difference between edema neuron cell model and normal neuron cell model is 0.206 degree.The main features of the research are as follows:1. The precision of phase detection is up to 0.02 degree by the high-precision phase change detector, SR844.2. The interference resulted from phase shift of the unit is decreased by using the new detection method.3. The neuron cell experiment is made to detect the phase change produced by edema neuron cell model, contrasting to that of normal neuron cell model.The unit designed has a high precision of detecting phase changes and the capability of detecting the phase changes of edema neuron cell model and normal neuron cell model effectively. The cells experiment starts the research of the cerebral edema on the level of cell. These may be of great help for further cerebral edema-detecting work.