Schuessler T F, Bates J H
Department of Biomedical Engineering, McGill University, Montréal, Québec, Canada.
Ann Biomed Eng. 1998 Mar-Apr;26(2):253-9. doi: 10.1114/1.116.
Electrical impedance tomography (EIT) estimates the spatial distribution of the electrical tissue properties in a cross section of the body. In the present study, we investigated how the quality of static thoracic images obtained from EIT systems with a single current source and sink is affected by the current pattern employed in the presence of measurement noise. The reconstructed images best reproduced our computational phantom when current source and sink were placed at neighboring electrodes. In this case, the mean squared reconstruction error was an order of magnitude smaller than for all other patterns of current injection studied. At a signal-to-noise ratio of 50 dB, 60% of the reconstructions converged successfully with source and sink at neighboring electrodes, while only 10% or less converged for all other configurations. We relate these results to the fact that neighboring currents strengthen the diagonal structure in the Hessian matrix of the iterative reconstruction process that we employed. We also tested the effects on the reconstruction error of the number and type of electrodes. We found that "compound electrodes" that permit voltage measurement at the site of current injection did not yield any practical improvement of the image quality. In contrast, doubling the number of boundary electrodes reduced the reconstruction error by almost two orders of magnitude.
电阻抗断层成像（EIT）可估计人体横截面中电组织特性的空间分布。在本研究中，我们调查了在存在测量噪声的情况下，采用单电流源和电流汇的EIT系统所获得的静态胸部图像质量如何受到所采用电流模式的影响。当电流源和电流汇置于相邻电极时，重建图像能最佳地再现我们的计算体模。在这种情况下，均方重建误差比所研究的所有其他电流注入模式小一个数量级。在信噪比为50 dB时，60%的重建在电流源和电流汇位于相邻电极时成功收敛，而在所有其他配置下只有10%或更少的重建收敛。我们将这些结果与相邻电流加强我们所采用的迭代重建过程的海森矩阵中的对角结构这一事实联系起来。我们还测试了电极数量和类型对重建误差的影响。我们发现，允许在电流注入部位进行电压测量的“复合电极”并未对图像质量产生任何实际改善。相比之下，将边界电极数量加倍可使重建误差降低近两个数量级。
