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摘要:
针对电磁层析成像(EMT)逆问题中,灵敏度矩阵的病态性、不适定性等问题,提出了一种新的电磁层析图像快速重建算法。利用主成分分析(PCA)对灵敏度矩阵做降维映射,再利用奇异值分解(SVD)求广义逆矩阵,重建图像。在选取灵敏度矩阵的协方差矩阵的特征值个数中,利用灵敏度矩阵特有的多样本特性,提出图像相关系数最大化算法,更加合理地去除灵敏度矩阵中的冗余信息,在尽可能不丢失成像特征信息的条件下,提高了解稳定性。实际采集数据成像时,该算法只需一次矩阵乘法运算,为快速实时成像提供了可能。与传统单步算法和迭代算法相比,该算法在成像质量和速度上都有较明显优势。
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关键词:
- 电磁层析成像(EMT) /
- 主成分分析(PCA) /
- 奇异值分解(SVD) /
- 图像相关系数最大化 /
- 降维
Abstract:For the inverse problem of electromagnetic tomography (EMT), the pathological and ill posed problems of the sensitivity matrix are discussed. A new electromagnetic tomography image reconstruction algorithm is proposed for this situation. Firstly, the principal component analysis (PCA) is used to reduce the dimension of the sensitivity matrix, and then the singular value decomposition (SVD) is used to calculate the generalized inverse matrix to reconstruct the image. After the covariance matrix of the sensitivity matrix is obtained, we need to compute the number of eigenvalues that the covariance matrix should retain. Then the maximization of the image correlation coefficient algorithm is proposed to solve it by using the unique multi-sample characteristics of the sensitivity matrix. It is more reasonable for sensitivity matrix to remove redundant information. And it improves the stability of the solution as far as possible without losing imaging feature information. When the actual data is used for imaging, this algorithm needs only one matrix multiplication, which provides the possibility for fast real-time imaging. In conclusion, compared with the traditional single step algorithm and iterative algorithm, the proposed algorithm has obvious advantages in both imaging quality and speed.
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表 1 灵敏度矩阵降维前后多物体成像对比
Table 1. Multi-object imaging contrast before and after dimension reduction of sensitivity matrix
表 2 各算法多物体仿真成像对比
Table 2. Comparison of multi-algorithm and multi-object simulation imaging
表 3 仿真图像相关系数数据
Table 3. Image correlation coefficient data in simulation
样本类型 LBP法 Tikhonov
正则化法Landweber
迭代算法降维
SVD1物体 -0.010 0 0.506 4 0.787 1 0.801 5 2物体 -0.007 0 0.595 4 0.761 9 0.688 5 3物体 -0.027 4 0.538 6 0.707 9 0.652 5 4物体 -0.040 6 0.424 5 0.644 9 0.606 1 5长物体 -0.026 5 0.279 6 0.319 4 0.326 4 表 4 仿真图像相对误差数据
Table 4. Image relative error data in simulation
样本类型 LBP法 Tikhonov
正则化法Landweber
迭代算法降维
SV1物体 1.188 7 1.046 7 0.753 2 0.751 1 2物体 1.102 8 0.726 5 0.675 2 0.795 5 3物体 1.042 9 0.729 7 0.637 6 0.668 2 4物体 1.069 5 0.788 3 0.662 2 0.684 0 5长物体 3.422 0 0.886 5 0.868 8 0.875 2 表 5 各算法计算时间
Table 5. Calculation time of each algorithm
ms 样本类型 LBP法 Tikhonov
正则化法Landweber
迭代算法降维
SVD1物体 1.1 0.4 200.1 0.2 2物体 1.2 0.4 306.4 0.2 3物体 1.1 0.4 440.4 0.2 4物体 1.2 0.3 280.8 0.2 5长物体 1.2 0.4 453.2 0.2 表 6 各算法实验成像对比
Table 6. Comparison of multi-algorithm experimental imaging
表 7 实验图像相关系数数据
Table 7. Image correlation coefficient data in experiment
样本类型LBP法 Tikhonov
正则化法Landweber
迭代算法降维
SVD1物体 0.531 6 0.612 2 0.652 3 0.647 5 2物体 0.453 4 0.543 3 0.608 4 0.599 0 3物体 0.467 1 0.519 1 0.587 9 0.590 4 表 8 实验图像相对误差数据
Table 8. Image relative error data in experiment
样本类型 LBP法 Tikhonov
正则化法Landweber
迭代算法降维
SVD1物体 0.960 3 0.787 0 0.674 1 0.685 0 2物体 0.959 7 0.696 6 0.667 2 0.671 1 3物体 0.953 7 0.778 3 0.693 0 0.687 6 -
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