人大脑组织复电阻抗频率特性及其等效电路模型

背景电阻抗断层成像技术是对人体施加无伤害的电信号,通过体表测量其响应信号,用一定的重构算法得到人体内部的电阻抗或其变化的分布.在电阻抗断层成像中,各种组织的电阻抗频率特性对于利用电阻抗断层成像技术对病灶进行成像、定位或监测至关重要.目的测量出人脑组织的电阻抗频率特性,并与已知的人体其他生物组织已知谱线和家兔脑组织曲线相比较.设计观察性实验.单位解放军第四军医大学生物医学工程系医学电子工程教研室.对象实验于2000-04/06在解放军第四军医大学生物医学工程系医学电子工程教研室电阻抗断层成像实验室完成.两例人脑组织来自解剖教学用新鲜尸体,死亡时间＜12 h,成年男性.干预分割2个人脑组织共得到15个样本,利用英国Solartron公司频率响应分析仪(1255B),阻抗接口(1294)以及自制的测量盒,采用4电极分别测量出0.1～1×106Hz频率范围内离体脑组织的复电阻抗频率特性.主要观察指标在0.1～1×106Hz频率范围内电阻率频率特性曲线,复电阻抗实部、虚部频率特性曲线,复电阻抗等效电路模型.结果人脑组织电阻率在0.1～100Hz频率范围内约为1 200Ω·cm,在100～1×106Hz频率范围内随着频率的增高而减小至650 Ω·cm.人脑组织复电阻抗实部在0.1～100 Hz频率范围内比较稳定,在100～1×106 H2频率范围内随着频率的增高而减小.人脑组织复电阻抗虚部绝对值的频率特性曲线呈单调上升趋势.结论人脑组织电阻率、复电阻抗实部频率特性曲线与其他生物组织(如肌肉、肝、肾、肺等)的谱线一致.人脑组织复电阻抗虚部绝对值的频率特性曲线同已知的其他动物组织(肌肉、肝、肾等)的复电阻抗虚部频率特性相比不同,但与离体家兔脑组织的曲线一致.脑组织的复电阻抗等效电路模型比已知的生物组织等效电路模型要复杂.

Complex impedance frequency response of human brain tissues and its equivalent circuit model

BACKGROUND:The electrical impedance tomography (EIT) is a kind of examination that is used to non-invasively measure the change and distribution of electrical bio-impedance by reconstructing the frequency response obtained by electrical stimuli applied onto the human body. The characteristics of impedance of any tissues are of great importance to the imaging of EIT and locating and monitoring the lesion focus.OBJECTIVE: To measure the human brain impedance in the frequency range from 0.1 Hz to 1 MHz and to compare these with those of other human tissues and the rabbit brain tissues.DESIGN: An observational experiment.SETTING:The Department of Medical Electric Engineering of the Biomedical Engineering College of the Fourth Military Medical University of Chinese PLA.MATERIALS:The experiment was conducted at the Otolaryngology Laboratory, Department of Medical Electric Engineering of Biomedical Engineering College, Fourth Military Medical University of Chinese PLA from April, 2000 to June, 2000. Two brains were harvested from two cadavers of adult men who died in less than 12 hours before the brains were taken.INTERVENTIONS :The brains were divided into 15 samples and the Solartron 1255B frequency resoonse analyzer was used to measure the complex impedance of human brain in vitro with four-electrode measurement method in the frequency range from 0.1 Hz to 1 MHz.There were also impedance interface (1294)and self-made experimental measurement box.MAIN OUTCOME MEASURES:The resistivity frequency response,curves of real part and imaginary part of complex impedance as well as the equivalent circuit model of the complex impedance.RESULTS:The resistivity of human brain tissues was about 1 200 Ω·cm in the frequency range of 0.1-100 Hz. But it decreased to 650 Ω·cm in the frequency range of 100-1×106 Hz. The real part of complex impedance remained steady in the frequency range of 0.1-100 Hz and it decreased along with the increase of frequency in the range of 100-1×106 Hz. The absolute value of frequency response curves of the imaginary part of human brain's complex impedance presented a tendency of monotonic increase.CONCLUSION: The resistivity and the real part of complex impedance curve of human brain were in accordance with those of other tissues such as muscles, the liver, kidney and lungs. The frequency response curve of the imaginary part of human brain's complex impedance was different from that of other animal tissues (such as muscles, the liver and kidney) but was in accordance with that of rabbit brain tissues in vitro. The construction of the equivalent circuit model obtained was more complex than other models known.