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面向生物磁感应成像的线圈阵列优化与测量方法研究
【作者】 陈龙；
【导师】 狄长安；
【作者基本信息】 南京理工大学 ， 测试计量技术及仪器， 2017， 硕士
【摘要】 磁感应断层成像技术作为一种新兴的非接触式生物组织成像技术,是当今生物医学工程无损检测的热点之一。针对生物磁感应成像中强背景下有效信号的提取难题,开展面向生物磁感应成像线圈阵列优化和测量方法的研究,以提高测量信号的信噪比。根据电磁感应耦合理论,基于生物EMT检测系统线圈传感器和被测生物组织的电路模型分别对其阻抗特性进行了仿真计算与分析,采用等效电路法建立了生物电磁感应层析成像的谐振能量耦合模型。基于Matlab的数值分析,得出了线圈品质因数、耦合系数、传感器安装个数及位置等参数对耦合模型的影响,确定了激励线圈品质因数为影响传感器及测量系统输出的关键调控因素。针对检测线圈与激励线圈之间的干扰问题,提出了空间阵列四通道生物EMT检测模型,并对该检测模型的特性进行了仿真分析与研究;根据现有的激励传感器参数,基于虚拟正交响应面法对激励传感器的参数进行了仿真优化;基于相关分析方法实验研究了检测线圈传感器的选取与匹配;针对高频成像系统容易受到外界的噪声干扰,引入屏蔽技术,对屏蔽层的关键参数进行了仿真与实验研究,并完成了传感器阵列载体结构的设计及材料选型。设计了生物EMT检测电路,确定了鉴相方法。仿真分析了高频特征下FFT等鉴相算法的鉴相精度与采样率及信噪比之间的关系;分析了检测线圈空场试验下所叠加的噪声特性,采用小波去噪与中值滤波的混合去噪方法可以有效抑制高斯及脉冲干扰。实验研究了低电导率盐溶液空间位置变化、电导率变化及异物干扰对检测系统输出信号的影响,实验结果表明,基于正交差分的空间阵列EMT系统在减小了线圈间的耦合作用下,提高了成像系统的灵敏度,且系统检测线性区间的下限值提高至0.25S/m,在0.60～1.40S/m范围内线性化程度较高;针对旋转测量周期长的问题,进行了旋转测量方法的优化,在均匀被测物下利用多通道线圈数据融合测量可以有效减少检测数据的冗余输出。
【Abstract】 As a new non-contract biological tissues imaging technology,Magnetic Induction Tomography(MIT)is one of the most advanced topics in the field of nondestructive examination(NDE)for today’s biomedical engineering.Based on this,aiming at the problem that the effective signal is difficult to extract under the strong background signal in the biological detection,this paper focuses on the optimization and measurement method of the biological magnetic induction imaging coil array to improve the accuracy of the measurement signal.According to the electromagnetic induction coupling theory,the impedance characteristics of the bio-EMT detection system coil sensor and the measured biological tissue circuit model have been simulated and analyzed respectively.And the resonant energy coupling model of bio-electromagnetic induction tomography is established by the equivalent circuit method.Based on the numerical analysis of Matlab,the influences of the coil quality factor,the coupling coefficient,the number of sensors and the positions of the sensors on the coupled model are obtained,and the quality factor of the exciting coil is determined as the key controlling factor for the influence of sensor and the output of measurement system.Aiming at the interference between the detection coil and the excitation coil,a four-channel bio-EMT detection model for the space array is proposed,and the characteristics of the detection model are analyzed and studied empirically.According to the existing excitation sensor parameters,the excitation sensor parameters are simulated and optimized.Based on the correlation analysis method,the selection and matching of detection coil sensor are studied experimentally,for high-frequency imaging system,which is vulnerable to external noise interference,the shielding technology is introduced.The key parameters of the shielding were simulated and experimentally researched,and the sensor array carrier structure design and material selection are completed.The detection circuit of biological EMT detection device designed and the phase detection method is determined.The simulation analyzes the phase precision and the relationship between sample rate and noise-signal ratio of FFT and other phase detection algorithmsin the high frequency condition.Moreover,the superposed noise characteristics of the detection coil under the openstope test are analyzed,showing that the mixed denoising method using wavelet denoising and median filtering can effectively suppress the Gaussian and pulse interference.The influence of spatial position changes of low-conductivity salt solution,the changes of electrical conductivity and the foreign matter interference on the output signal of the detection system has been studied at the experiment.The experimental results show that the lower limit of the linear interval,which is based on the orthogonal difference and on the condition of reducing the coupling effect between the coils,decreased to 0.25S/m,and has relatively high linearization at the range from 0.60S/m to 1.40S/m.In addition,the rotation measurement method has been optimized for the long measurement period caused by rotation measurement of spatial array.And the multi-channel coil combination measurement to reduce data redundancy has been studied and experimentally analyzed.