磁共振力显微镜的信号处理与图像复原研究
发布时间：2018-09-12 05:16
【摘要】：磁共振力显微镜是一种能实现纳米级分辨率的三维分子成像仪器,它结合了磁共振成像技术与扫描探针显微术,具有磁共振成像的三维探测能力与扫描探针显微术的纳米分辨能力,可以实现单个核自旋的探测。然而,磁共振力显微镜在实际应用中存在扫描速度慢、易受噪声影响和成像速度慢等问题,解决这些问题有赖于有效、精妙的信号处理方法和图像处理方法的运用。本文研究了磁共振力显微镜涉及的一些的信号处理方法和图像处理方法,包括四个方面:带噪正弦信号的参数估计、ARMA模型在微悬臂的系统辨识中的应用、样品自旋密度图像的复原、扩频及解扩方案的设计。主要的研究工作和创新点如下:(1)本文研究了带噪正弦信号的参数估计。根据信号携带的噪声的统计特性,使用分段幅度及相位联合最大似然估计来估计带噪正弦信号的幅度及相位,仿真研究表明估计算法的估计误差的方差很接近Cramer-Rao下界,估计性能良好。(2)为了了解微悬臂的模态信息,本文采用ARMA模型对微悬臂进行系统辨识和模态参数识别。针对观测噪声会使时间序列模型的辨识精度变低的问题,本文研究了如何将带有观测噪声的ARMA模型转化为无观测噪声的ARMA模型。得到微悬臂的ARMA模型后将这个模型转化为连续系统的传递函数,再从传递函数中求出微悬臂的各模态参数。为了减小微悬臂对外力的延迟响应时间从而提高磁共振力显微镜的扫描速度,本文根据系统辨识得到的模型,构造一个复原滤波器,微悬臂的振动信号通过这个复原滤波器后得到作用力信号。仿真及实验结果表明了本文所用的系统辨识、模态参数识别及信号复原方法的有效性。(3)为了从退化图像中恢复出自旋密度图像,本文研究了磁共振力显微镜的成像机理和自旋密度图像的复原方法。根据磁共振力显微镜的成像机理,推导了点扩散函数的表达式。当点扩散函数容易求得时,考虑图像复原问题的病态性,用基于稀疏性约束的非盲图像复原算法进行图像复原;当点扩散函数不容易求得时,用盲图像复原算法进行图像复原,同时复原出点扩散函数和自旋密度图像。(4)为了提高磁共振力显微镜的抗干扰性,本文提出了一个扩频及解扩方案,这个方案对磁共振力显微镜的输入信号进行扩频,并对输出信号进行解扩。本文用信号处理的理论研究了这个方案的抗干扰性,并与未施加扩频的方案进行比较,发现在一定条件下提出的方案的抗干扰性更佳。最后用仿真实验来证明这个方案的有效性。
[Abstract]:Magnetic resonance force microscopy (MRFM) is a three-dimensional molecular imaging instrument with nanometer resolution. It combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). It has the three-dimensional detection ability of magnetic resonance imaging (MRI) and the nanometer resolution ability of scanning probe microscopy (SPM). It can detect the spin of a single nucleus. There are some problems in practical application, such as slow scanning speed, easy to be affected by noise and slow imaging speed. To solve these problems, it is necessary to use effective and delicate signal processing methods and image processing methods. Parameter estimation of sinusoidal signal, application of ARMA model in system identification of micro-cantilever, restoration of sample spin density image, design of spread spectrum and despreading scheme. The main research work and innovation are as follows: (1) Parameter estimation of noisy sinusoidal signal is studied in this paper. Bit joint maximum likelihood estimation is used to estimate the amplitude and phase of the noisy sinusoidal signal. Simulation results show that the variance of the estimation error is close to Cramer-Rao lower bound and the estimation performance is good. (2) In order to understand the modal information of the micro-cantilever, the ARMA model is used to identify the system and modal parameters of the micro-cantilever. In this paper, we study how to transform the ARMA model with observation noise into the ARMA model without observation noise. After obtaining the ARMA model of the micro-cantilever, the model is transformed into the transfer function of the continuous system, and then the modal parameters of the micro-cantilever are obtained from the transfer function. In order to reduce the delay response time of the micro-cantilever to the external force and improve the scanning speed of the magnetic resonance force microscope, a restoring filter is constructed according to the model of the system identification. The vibration signal of the micro-cantilever passes through the restoring filter to get the force signal. (3) In order to recover the spin density image from the degraded image, the imaging mechanism of the magnetic resonance force microscope and the restoration method of the spin density image are studied in this paper. Then, considering the ill-conditioned of the image restoration problem, a non-blind image restoration algorithm based on sparse constraints is used to restore the image. When the point spread function is not easy to obtain, the blind image restoration algorithm is used to restore the image, and the point spread function and the spin density image are restored simultaneously. (4) To improve the anti-interference ability of the magnetic resonance force microscope, In this paper, a spread spectrum and despread scheme is proposed, which spread spectrum the input signal of the magnetic resonance force microscope and despread the output signal. The anti-jamming performance of this scheme is studied with the theory of signal processing, and compared with the scheme without spread spectrum, it is found that the anti-jamming of the scheme proposed under certain conditions. It is proved that the scheme is effective.
【学位授予单位】：中国科学院大学(中国科学院武汉物理与数学研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP391.41
本文编号：2238019
[Abstract]:Magnetic resonance force microscopy (MRFM) is a three-dimensional molecular imaging instrument with nanometer resolution. It combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). It has the three-dimensional detection ability of magnetic resonance imaging (MRI) and the nanometer resolution ability of scanning probe microscopy (SPM). It can detect the spin of a single nucleus. There are some problems in practical application, such as slow scanning speed, easy to be affected by noise and slow imaging speed. To solve these problems, it is necessary to use effective and delicate signal processing methods and image processing methods. Parameter estimation of sinusoidal signal, application of ARMA model in system identification of micro-cantilever, restoration of sample spin density image, design of spread spectrum and despreading scheme. The main research work and innovation are as follows: (1) Parameter estimation of noisy sinusoidal signal is studied in this paper. Bit joint maximum likelihood estimation is used to estimate the amplitude and phase of the noisy sinusoidal signal. Simulation results show that the variance of the estimation error is close to Cramer-Rao lower bound and the estimation performance is good. (2) In order to understand the modal information of the micro-cantilever, the ARMA model is used to identify the system and modal parameters of the micro-cantilever. In this paper, we study how to transform the ARMA model with observation noise into the ARMA model without observation noise. After obtaining the ARMA model of the micro-cantilever, the model is transformed into the transfer function of the continuous system, and then the modal parameters of the micro-cantilever are obtained from the transfer function. In order to reduce the delay response time of the micro-cantilever to the external force and improve the scanning speed of the magnetic resonance force microscope, a restoring filter is constructed according to the model of the system identification. The vibration signal of the micro-cantilever passes through the restoring filter to get the force signal. (3) In order to recover the spin density image from the degraded image, the imaging mechanism of the magnetic resonance force microscope and the restoration method of the spin density image are studied in this paper. Then, considering the ill-conditioned of the image restoration problem, a non-blind image restoration algorithm based on sparse constraints is used to restore the image. When the point spread function is not easy to obtain, the blind image restoration algorithm is used to restore the image, and the point spread function and the spin density image are restored simultaneously. (4) To improve the anti-interference ability of the magnetic resonance force microscope, In this paper, a spread spectrum and despread scheme is proposed, which spread spectrum the input signal of the magnetic resonance force microscope and despread the output signal. The anti-jamming performance of this scheme is studied with the theory of signal processing, and compared with the scheme without spread spectrum, it is found that the anti-jamming of the scheme proposed under certain conditions. It is proved that the scheme is effective.
【学位授予单位】：中国科学院大学(中国科学院武汉物理与数学研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP391.41
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