IEEE Trans Biomed Eng. 2024 Nov;71(11):3283-3292. doi: 10.1109/TBME.2024.3416440. Epub 2024 Oct 25.
High-frequency oscillations (HFOs) are a promising prognostic biomarker of surgical outcome in patients with epilepsy. Their rates of occurrence and morphology have been studied extensively using recordings from electrodes of various geometries. While electrode size is a potential confounding factor in HFO studies, it has largely been disregarded due to a lack of consistent evidence. Therefore, we designed an experiment to directly test the impact of electrode size on HFO measurement.
We first simulated HFO measurement using a lumped model of the electrode-tissue interaction. Then eight human subjects were each implanted with a high-density 8x8 grid of subdural electrodes. After implantation, the electrode sizes were altered using a technique recently developed by our group, enabling intracranial EEG recordings for three different electrode surface areas from a static brain location. HFOs were automatically detected in the data and their characteristics were calculated.
The human subject measurements were consistent with the model. Specifically, HFO rate measured per area of tissue decreased significantly as electrode surface area increased. The smallest electrodes recorded more fast ripples than ripples. Amplitude of detected HFOs also decreased as electrode surface area increased, while duration and peak frequency were unaffected.
These results suggest that HFO rates measured using electrodes of different surface areas cannot be compared directly.
This has significant implications for HFOs as a tool for surgical planning, particularly for individual patients implanted with electrodes of multiple sizes and comparisons of HFO rate made across patients and studies.
高频振荡（HFOs）是癫痫患者手术结果的有前途的预后生物标志物。已经使用各种几何形状的电极记录广泛研究了它们的发生频率和形态。虽然电极尺寸是 HFO 研究中的一个潜在混杂因素，但由于缺乏一致的证据，它在很大程度上被忽视了。因此，我们设计了一项实验来直接测试电极尺寸对 HFO 测量的影响。
我们首先使用电极-组织相互作用的集中模型模拟 HFO 测量。然后，八名人类受试者每人都植入了一个高密度 8x8 网格的硬脑膜下电极。植入后，我们使用我们小组最近开发的技术改变了电极尺寸，从而能够从静态脑位置记录三个不同电极表面积的颅内 EEG 记录。在数据中自动检测 HFO 并计算其特征。
人体测量结果与模型一致。具体而言，随着电极表面积的增加，每单位组织测量的 HFO 率显着降低。最小的电极记录的快尖波比尖波多。随着电极表面积的增加，检测到的 HFO 的幅度减小，而持续时间和峰值频率不受影响。
这些结果表明，使用不同表面积的电极测量的 HFO 率不能直接比较。
这对 HFO 作为手术计划工具具有重要意义，特别是对于植入多个尺寸电极的个体患者以及在患者和研究之间进行 HFO 率比较。
