Abstracts

Rationale: Metal scalp electrodes in CT or MRI cause major artefacts or raise safety concerns with respect to heating. Thus, MRI and CT compatible electrodes are highly desirable for patients who need continuous EEG-recording, but also frequent MR- or CT-based imaging throughout their evaluation. Methods: Three types of electrodes were tested for compatibility and safety with MRI imaging: 1) gold-coated disc electrodes; 2) conductive plastic disc electrodes; 3) subdermal wire electrodes (SWE). To reduce susceptibility artefacts and induction, the electrode systems are designed with: no magnetic material, low metallic content, short as possible lead length and small plastic mass connectors. Four healthy subjects underwent MR imaging with a variable combination of the 3 types of electrodes (up to 32 electrodes). For CT imaging, a plexiglas phantom head was used. MRI images were acquired on a 3 Tesla MRI. T1, T2, FLAIR, Diffusion and functional MRI (fMRI) sequences were obtained. The same acquisition protocol was performed without the electrodes on the same subjects. Temperature was measured with a 4-channel optical thermometer. The SWE/plastic disc electrodes were subsequently used in the local Intensive Care Unit (ICU) in 13 comatose and non-comatose patients. Results: Structural and diffusion MR images as well as fMRI images obtained with the electrodes were of excellent quality and did not differ from images without electrodes. For CT imaging, plastic electrodes and SWE led to good image quality, whereas metal electrodes caused massive artefacts. Due to radio-frequency field heterogeneity, warming was variable and maximal in the occipital regions during T2 (at 100% SAR) and FLAIR sequences (+1,5 °C). In ICU patients, long-term EEG required low maintenance, while allowing simultaneous good-quality imaging tests. CT, MRI or digital angiography were performed in half of the patients during the monitoring. Conclusions: CT and MRI can be safely acquired with these new scalp or subdermal wire electrodes and image quality was not affected. This improves patient management in the ICU and opens new avenues of clinical and basic neuroscience research.