单通道BMIT系统中相位差的理论计算与实际检测

Theoretical Calculation and Experimental Detection of Phase Shift in Our Single-channel BMIT

目的:研究单通道脑磁感应成像系统中相位差的理论计算与实际检测的相关性,为系统的优化和实验改进提供理论依据。方法:单通道脑磁感应成像系统是基于高精度射频锁定放大器SR844建立的,该系统的工作频率为1MHz,包括一个激励线圈和一个检测线圈,被测目标置于两线圈之间以检测其相位差;针对该实验系统建立数学模型,推导被测目标靠近检测线圈时相位差计算公式;配制电导率为0S/m～2S/m的琼脂模型进行实验,对理论计算结果进行验证;并以培养的SD大鼠大脑皮质的神经细胞模型为检测对象进行实验。结果:检测结果与理论计算结果的趋势一致,相位差与被测目标的电导率和体积成正比。神经细胞模型引起的相位差为0.421°±0.018°;琼脂糖模型引起的相位差为0.382°±0.013°。结论:该系统能有效地检测出目标相位差,为进一步实现脑磁感应成像打下了良好的基础。

Objective： To study of the correlation between theoretical calculation and experimental detection of phase shift, optimize our experiment system and improve experimental methods in our single-channel BMIT system. Methods： Based on RF Lock-in amplifier SR844 our experiment system was designed at its operating frequency of 1 MHz, including an excitation coil and a detection coil. According to our system a mathematical model was established for the theoretical calculation, and its analytical formulas of phase shift were developed when an object was located near the detection coil. Experimental results were obtained for agar models with conductivities ranging from 0 S/m to 2 S/m, and were compared with the results of theoretical calculation. An experiment with neuron cell models from SD rat cortex was made and some effective data were obtained. Results： There is good agreement between the analytical and experimental results, the phase shift increases with conductivity and volume of objects. The phase shift of the neuron cell models was 0.421°±0.018°, and the phase shift of agarose models was 0.382°±0.013°. Conclusion： The system can effectively detect the phase shift of objects designed. These may be of great help for further brain magnetic induction tomography.