基于频域的磁声耦合成像方法研究

发布时间：2018-07-05 08:42

本文选题：磁声耦合成像 + 频域　；参考：《北京协和医学院》2014年博士论文

【摘要】：磁声耦合成像是一种新型无创生物组织电特性功能成像技术,具有超声成像高空间分辨率和电阻抗成像高对比度的优势,在肿瘤早期诊断方面具有重要的应用价值。微弱声信号的检测和处理是磁声成像重要的研究内容,对图像对比度和成像精度起关键作用。目前磁声耦合成像通常采用时域的信号检测处理方法,采用kV级高压μs窄脉冲进行激励以达到mm分辨率,其激励源设计实现难度较大,同时存在一定安全性问题,且时域方法检测易受到高频空间电磁场耦合干扰,限制了成像质量。针对目前时域磁声耦合成像方法存在的问题,本文提出频域的磁声成像方法,采用kHz连续正弦信号激励,其产生的声信号在kHz频段,衰减远小于MHz频段,简化了实验成像装置。另外,频域信号的检测采用锁相放大技术,对微弱声信号频域信息的检测放大,提高了信号检测精度,实现不同频率的信号幅值相位信息的测量,通过基于频域检测的图像重建算法,实现组织声源电导率分布图像的重建。本文依据波动方程建立了频域磁声耦合正问题的数学模型；基于正弦波激励,采用复平面矢量叠加求和方法,对频域磁声耦合正问题即磁声信号幅值相位进行求解；并通过数值求解和解析解,对简单电导率边界仿体边界声源进行了仿真研究,基于复平面声源矢量叠加方法分析了不同模型下的频域幅值和相位特性。搭建频域磁声成像实验系统,设计基于虚拟仪器平台的扫描检测系统的驱动控制程序,实现了成像实验系统的同步驱动控制采集和数据预处理,进行了频域方法的电导率边界模型的实验研究,验证频域磁声耦合数学模型和仿真研究结果。最后建立了频域磁声成像逆问题模型,利用优化算法对求解电导率分布的频域磁声耦合逆问题进行了仿真和实验研究。仿真研究表明,不同仿体的频域幅值随着声源空间位置、介质声源幅值的变化而变化,变化规律满足频域磁声耦合模型。同时对于相同介质模型在不同频率下,其对应的幅值和相位不同,且多层介质模型声源满足单层声源矢量的叠加求和规则。频域信号包含了电导率边界分布信息,通过锁相放大方法对频域磁声信号检测,可获取该电导率信息,同时降低了激励源的要求。实验结果表明,频域相位随距离变化规律满足频域磁声耦合理论与仿真结果,对于金属电导率边界模型,输出激励幅值达到1V以下时即可检测到磁声耦合声信号。磁声信号的检测精度得到提高,检测精度可达到10-7Pa,同时空间分辨率可达到mm量级。总之,本研究提出的频域磁声耦合成像方法,提高了微弱磁声信号检测精度,对实现磁声耦合介质内部电导率的检测和成像的研究具有重要意义。同时有利于降低磁声耦合激励源设计实现难度,简化磁声成像系统系统设计难度,对于磁声成像的实际应用提供了重要基础。
[Abstract]:Magnetoacoustic coupling imaging is a new type of non-invasive biological tissue electrical functional imaging technology, with the advantages of high spatial resolution ultrasound imaging and electrical impedance imaging high contrast, and has an important application value in the early diagnosis of tumor. Weak acoustic signal detection and processing is an important research content in magnetoacoustic imaging, which plays a key role in image contrast and imaging accuracy. At present, the magnetoacoustic coupling imaging usually uses the signal detection and processing method in time domain, and uses the kV high voltage 渭 s narrow pulse to excite to achieve the mm resolution. The design and realization of the excitation source is difficult, and there are some safety problems at the same time. Time domain detection is easy to be interfered by high frequency spatial electromagnetic field coupling, which limits the imaging quality. Aiming at the problems existing in the magnetoacoustic coupling imaging method in time domain, a frequency domain magnetoacoustic imaging method is proposed in this paper. The kHz continuous sinusoidal signal is used to excite the generated acoustic signal in the kHz band, and the attenuation is much less than that in the MHz band, which simplifies the experimental imaging device. In addition, the frequency domain signal is detected by phase-locked amplification technique, which amplifies the frequency domain information of weak acoustic signal, improves the signal detection precision, and realizes the measurement of amplitude and phase information of different frequency signal. The image reconstruction algorithm based on frequency domain detection is used to reconstruct the image of the conductivity distribution of the organization sound source. In this paper, the mathematical model of magnetoacoustic coupling forward problem in frequency domain is established according to the wave equation, and based on sine wave excitation, the amplitude and phase of magnetoacoustic signal are solved by using the method of superposition of complex plane vector. Numerical and analytical solutions are used to simulate the sound source with simple conductivity boundary. The amplitude and phase characteristics of different models in frequency domain are analyzed based on the method of complex plane sound source vector superposition. The frequency domain magnetoacoustic imaging experiment system is built, and the drive control program of scanning detection system based on virtual instrument platform is designed. The synchronous drive control acquisition and data preprocessing of imaging experimental system are realized. The conductivity boundary model of frequency-domain method is studied experimentally, and the results of magneto-acoustic coupling mathematical model and simulation in frequency-domain are verified. Finally, the inverse problem model of frequency-domain magnetoacoustic imaging is established, and the simulation and experiment of the frequency-domain magnetoacoustic coupling inverse problem of conductivity distribution are carried out by using the optimization algorithm. The simulation results show that the amplitudes in frequency domain vary with the spatial position of sound source and the amplitude of medium sound source, and the variation law satisfies the magnetoacoustic coupling model in frequency domain. At the same time, the amplitude and phase of the same media model are different at different frequencies, and the multi-layer media model sound source satisfies the superposition and summation rule of the single layer sound source vector. The frequency-domain signal contains the boundary distribution information of conductivity, which can be obtained by detecting the frequency-domain magnetoacoustic signal by the phase-locked amplification method, and the requirement of excitation source is reduced at the same time. The experimental results show that the frequency-domain phase variation with the distance satisfies the frequency-domain magnetoacoustic coupling theory and simulation results. For the metal conductivity boundary model, the magnetoacoustic coupling signal can be detected when the output excitation amplitude is less than 1V. The detection accuracy of magnetoacoustic signal is improved, the detection accuracy can reach 10 ~ (-7) Pa, and the spatial resolution can reach the magnitude of mm. In conclusion, the frequency domain magnetoacoustic coupling imaging method proposed in this paper improves the detection accuracy of weak magnetoacoustic signals, and is of great significance to the detection and imaging of the internal conductivity of magnetoacoustic coupling medium. At the same time, it is helpful to reduce the difficulty of design and realization of magnetoacoustic coupling excitation source and simplify the design difficulty of magnetoacoustic imaging system, which provides an important foundation for the practical application of magnetoacoustic imaging.
【学位授予单位】：北京协和医学院
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN911.23;R730.4

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