Fabrizi L, Sparkes M, Horesh L, Perez-Juste Abascal J F, McEwan A, Bayford R H, Elwes R, Binnie C D, Holder D S
Department of Medical Physics and Bioengineering, University College London, London WC1E 6BT, UK.
Physiol Meas. 2006 May;27(5):S163-74. doi: 10.1088/0967-3334/27/5/S14. Epub 2006 Apr 20.
Electrical impedance tomography (EIT) has the potential to produce images during epileptic seizures. This might improve the accuracy of the localization of epileptic foci in patients undergoing presurgical assessment for curative neurosurgery. It has already been shown that impedance increases by up to 22% during induced epileptic seizures in animal models, using cortical or implanted electrodes in controlled experiments. The purpose of this study was to determine if reproducible raw impedance changes and EIT images could be collected during epileptic seizures in patients who were undergoing observation with video-electroencephalography (EEG) telemetry as part of evaluation prior to neurosurgery to resect the region of brain causing the epilepsy. A secondary purpose was to develop an objective method for processing and evaluating data, as seizures arose at unpredictable times from a noisy baseline. Four-terminal impedance measurements from 258 combinations were collected continuously using 32 EEG scalp electrodes in 22 seizure episodes from 7 patients during their presurgical assessment together with the standard EEG recordings. A reliable method for defining the pre-seizure baseline and recording impedance data and EIT images was developed, in which EIT and EEG could be acquired simultaneously after filtering of EIT artefact from the EEG signal. Fluctuations of several per cent over minutes were observed in the baseline between seizures. During seizures, boundary voltage changes diverged with a standard deviation of 1-54% from the baseline. No reproducible changes with the expected time course of some tens of seconds and magnitude of about 0.1% could be reliably measured. This demonstrates that it is feasible to acquire EIT images in parallel with standard EEG during presurgical assessment but, unfortunately, expected EIT changes on the scalp of about 0.1% are swamped by much larger movement and systematic artefact. Nevertheless, EIT has the unique potential to provide invaluable neuroimaging data for this purpose and may still become possible with improvements in electrode design and instrumentation.
电阻抗断层成像（EIT）有潜力在癫痫发作期间生成图像。这可能会提高接受根治性神经外科手术术前评估的患者癫痫病灶定位的准确性。在动物模型的对照实验中，已使用皮层电极或植入电极证明，在诱发癫痫发作期间，阻抗可增加高达22%。本研究的目的是确定在接受视频脑电图（EEG）遥测观察的患者癫痫发作期间，是否能够收集到可重复的原始阻抗变化和EIT图像，这些患者作为神经外科手术切除引起癫痫的脑区术前评估的一部分。第二个目的是开发一种客观的方法来处理和评估数据，因为癫痫发作在嘈杂的基线中不可预测的时间出现。在7名患者术前评估期间的22次癫痫发作中，使用32个EEG头皮电极连续收集了258种组合的四端阻抗测量值，并同时进行标准EEG记录。开发了一种可靠的方法来定义癫痫发作前的基线并记录阻抗数据和EIT图像，其中在从EEG信号中滤除EIT伪影后，可以同时采集EIT和EEG。癫痫发作之间的基线在数分钟内观察到有百分之几的波动。癫痫发作期间，边界电压变化与基线的标准差相差1 - 54%。无法可靠地测量到与预期的几十秒时间进程和约0.1%幅度的可重复变化。这表明在术前评估期间与标准EEG并行采集EIT图像是可行的，但不幸的是，头皮上预期的约0.1%的EIT变化被更大的运动和系统伪影所淹没。尽管如此，EIT有独特的潜力为此目的提供宝贵的神经成像数据，并且随着电极设计和仪器的改进仍有可能实现。
