The effect of layers in imaging brain function using electrical impedance tomograghy
The effect of layers in imaging brain function using electrical impedance tomograghy
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DOI：
10.1088/0967-3334/25/1/022
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发表时间：
2004-02-01
影响因子：
3.2
通讯作者：
Holder, DS
中科院分区：
文献类型：
--
作者：
Liston, AD;Bayford, RH;Holder, DS
电阻抗断层扫描 (EIT) 有望通过头皮电极环对大脑功能进行成像，但迄今为止，人类图像是使用一种简单的算法来收集和重建的，其中头部被建模为均匀的球体。这项工作的目的是评估图像质量的改进，通过在重建算法采用的正向模型中添加代表脑脊液 (CSF)、头骨和头皮的层可以实现图像质量的改进。使用线性有限元法 (FEM) 分析得出正演模型的解。这是针对计算机模拟数据进行的，当球体电导率变化 10%、半径为 5 毫米时，移动通过建模为半径 80-92 毫米的四个同心球的头部内的 29 个位置，以便通过与分析方法进行比较来验证线性有限元法的准确性。测试数据还记录在一个 93.5 毫米球形、充满盐水的罐中，其中头骨由 5 毫米厚的熟石膏空心球体和 20 x 20 毫米直角圆柱形有机玻璃物体（电导率降低 100%）模拟，并移动通过 39 个位置。最佳图像是通过四壳或三壳分析模型重建获得的，计算机模拟的空间精度为 5.8 +/- 2.2 毫米，储罐数据的空间精度为 14.0 +/- 5.8 毫米。 XY 平面和 z 轴的平均半高宽分别为 57 毫米和 91 毫米。使用同质分析模型进行重建使定位误差增加了约 50-300%，但 FWHM 减少了图像直径的约 5%。出乎意料的是，使用有限元模型重建的结果与分析同质情况相似，结果较差。这证实了在正向模型中添加壳可以提高图像质量，正如重建分析模型所预期的那样，但是所采用的有限元方法（使用中等网格和线性元素计算）需要改进才能产生预期的效果。
Electrical impedance tomography (EIT) has promise for imaging brain function with rings of scalp electrodes, but hitherto human images have been collected and reconstructed using a simple algorithm in which the head was modelled as a homogeneous sphere. The purpose of this work was to assess the improvement in image quality which could be achieved by adding layers to represent the cerebro-spinal fluid (CSF), skull and scalp in the forward model employed by the reconstruction algorithm. Solutions to the forward model were produced analytically and using the linear finite element method (FEM). This was undertaken for computer simulated data when a spherical conductivity change of 10%, radius 5 mm, was moved through 29 positions within a head modelled as four concentric spheres of radius 80-92 mm in order to verify the accuracy of the linear FEM by comparison with the analytical method. Test data were also recorded in a 93.5 mm, spherical, saline-filled tank in which the skull was simulated by a hollow sphere of plaster of Paris, 5 mm thick and a 20 x 20 mm right-cylindrical Perspex object, a 100% conductivity decrease, was moved through 39 positions. The best images were achieved by reconstruction with a four- or three-shell analytical model, giving a spatial accuracy of 5.8 +/- 2.2 mm for computer simulated or 14.0 +/- 5.8 mm for tank data. Mean FWHM was 57 mm and 91 mm in the XY-plane and along the z-axis, respectively. Reconstruction with a homogeneous analytical model gave localization errors greater by about 50-300%, but a reduction in FWHM of about 5% of the image diameter. Unexpectedly, reconstruction with FEM models gave poorer results similar to the analytical homogeneous case. This confirms that addition of shells to the forward model improves image quality as expected with an analytical model for reconstruction, but that the FEM method employed, which used a medium mesh and a linear element computation, requires improvement in order to yield the expected benefits.