Boone K G, Holder D S
Department of Physiology, University College London, UK.
Med Biol Eng Comput. 1996 Sep;34(5):351-4. doi: 10.1007/BF02520003.
A computer simulation is used to investigate the relationship between skin impedance and image artefacts in electrical impedance tomography. Sets of electrode impedance are generated with a pseudo-random distribution and used to introduce errors in boundary voltage measurements. To simplify the analysis, the non-idealities in the current injection circuit are replaced by a fixed common-mode error term. The boundary voltages are reconstructed into images and inspected. Where the simulated skin impedance remains constant between measurements, large impedances (> 2k omega) do not cause significant degradation of the image. Where the skin impedances 'drift' between measurements, a drift of 5% from a starting impedance of 100 omega is sufficient to cause significant image distortion. If the skin impedances vary randomly between measurements, they have to be less than 10 omega to allow satisfactory images. Skin impedances are typically 100-200 omega at 50 kHz on unprepared skin. These values are sufficient to cause image distortion if they drift over time. It is concluded that the patient's skin should be abraded to reduce impedance, and measurements should be avoided in the first 10 min after electrode placement.
采用计算机模拟研究电阻抗断层成像中皮肤阻抗与图像伪影之间的关系。通过伪随机分布生成电极阻抗集，并用于在边界电压测量中引入误差。为简化分析，电流注入电路中的非理想特性由一个固定的共模误差项代替。将边界电压重建为图像并进行检查。在测量之间模拟皮肤阻抗保持恒定的情况下，大阻抗（>2kΩ）不会导致图像显著退化。在测量之间皮肤阻抗“漂移”的情况下，从100Ω的起始阻抗漂移5%就足以导致显著的图像失真。如果在测量之间皮肤阻抗随机变化，则其必须小于10Ω才能获得满意的图像。在未处理的皮肤上，50kHz时皮肤阻抗通常为100 - 200Ω。如果这些值随时间漂移，就足以导致图像失真。得出的结论是，应打磨患者皮肤以降低阻抗，并且应避免在放置电极后的前10分钟内进行测量。
