摘要
介绍一种均匀激励磁场磁感应成像的改进反投影算法。根据毕奥-萨伐尔定律和灵敏度的分布,提出以灵敏度为零的点作为分界点,采用不同方式的加权系数,对反投影算法进行修正。灵敏度分布的仿真实验表明,当检测线圈与成像区间的剖分单元之间的距离r等于0.06 m时,检测线圈上的测量电压的变化对距离r的变化的灵敏度为0,此时剖分单元的位置标记为P0。当检测线圈与剖分单元的距离r小于0.06 m时,反投影算法的加权系数取为r2;反之r大于等于0.06 m时,加权系数均为P0到检测线圈的距离r0的平方。不同位置的目标的实验结果表明,当异物位于成像区间的中心和偏离中心0.015 m时,都能准确反映异物的位置,但是当异物偏离中心0.03 m时,得到的成像结果比实际模型更偏离中心。不同大小的目标的实验结果表明,与实际模型中异物尺寸相比,直径较小的异物的成像基本能够反映出模型中实际异物的大小,而直径较大的异物的成像在尺寸上和位置上均难以体现模型中实际异物的真实形态。本研究提出的采用不同方式的加权系数的改进反投影算法,能一定程度上消除传统反投影算法中目标成像拖影范围较大的痼疾,对异物的定位较为准确,是一种在磁感应成像研究中值得推广的新方法。
This paper describes an improved back-projection algorithm of magnetic induction tomography with uniform magnetic excitation.According to Biot-Savart law and the distribution of the sensitivity,a new algorithm with mixed weight was proposed to correct back-projection algorithm.Considering the sensitivity of zero point as the dividing point,this algorithm used different weighting coefficients which were separated by the dividing point.According to the simulation experiment of sensitivity distribution,when the distance r from detection coil to the meshing element of imaging area was 0.06 m,the sensitivity value was zreo,and the position of this meshing element was marked P0.When the distance r from detection coil to meshing element was less than 0.06 m,the weighted coefficient was r2 ; otherwise,the weighting coefficients were the square of the distance r0from the detection coil to P0 point.The experimental results of different positions of foreign body showed that the back projection algorithm with mixed weight well reflected the size of the target object.When the foreign object was located in the center and 0.015 m off-center,the algorithm accurately reflected the position.However,when foreign object were 0.03 m off center,the location from the reconstructed image was more off-center than that of the actual model.The experimental results of different size of foreign body revealed that the reconstructed image of smaller diameter of the foreign object could accurately reflect the size of the foreign object,while that of larger diameter could not.The improved back projection algorithm can eliminate a wide range of smearing image errors caused by the conventional back-projection algorithm to a certain extent,and can also locate the foreign object more accurately.Therefore,the proposed algorithm is of significance in the study of magnetic induction image.
出处
《中国生物医学工程学报》
CAS
CSCD
北大核心
2014年第3期313-319,共7页
Chinese Journal of Biomedical Engineering
基金
国家自然科学基金(51107150)
中央高校基本科研业务经费资助项目(CDJZR10150021)
"111"计划项目(B08036)
关键词
磁感应成像
反投影算法
亥姆霍兹线圈
magnetic induction tomography
back projection algorithm
Helmholtz coil
