Feasibility and signal quality of the Minder® implantable continuous EEG monitoring® system compared to 10–20 scalp electrodes over extended monitoring periods

OBJECTIVE: To evaluate the signal quality of the Minder implantable continuous EEG monitoring (iCEM) system compared to traditional scalp EEG in the context of long-term, continuous monitoring in individuals with epilepsy. METHODS: Twenty-six patients implanted with the Minder iCEM system (November 2019 to July 2023) underwent 7-day video-EEG co-monitoring with full montage scalp EEG at 4 and 24 weeks post-implantation. Co-monitored EEG segments were rated for clarity on a 5-point ordinal scale by blinded expert reviewers for ictal and interictal periods. Minder vs scalp ratings were compared using Wilcoxon signed-rank test; 4- vs 24-week comparisons used Wilcoxon rank-sum test. Objective quantitative EEG analysis of the signal bandwidth was performed by application of spectral coherence analysis and Pearson's correlation coefficients. RESULTS: No significant difference was found between interictal signal clarity reviewer ratings for Minder vs scalp EEG (p = .97), and there was no statistically significant difference between the Minder signal clarity ratings at 4 vs 24 weeks (p = .95). Pearson's correlation between Minder vs scalp EEG also indicated a high degree of similarity (median correlation = .69) and no statistically significant difference between correlations at 4 vs 24 weeks (p = .99). All electrographic seizures identified on full 10-20 scalp EEG were also identified on Minder; however, the full 10-20 montage received statistically higher seizure clarity ratings than Minder (p < .001). SIGNIFICANCE: This study supports the feasibility of sub-scalp EEG as a reliable long-term monitoring tool. Interictal signal quality was statistically equivalent to limited-montage scalp EEG, and all seizures identified on full 10-20 scalp EEG were also visualized on Minder. The full 10-20 montage did receive statistically higher seizure clarity ratings, reflecting its greater spatial resolution. The signal quality was stable through 24 weeks, demonstrating the fidelity of the device. These findings position the Minder system as a complement to full montage scalp EEG, particularly in ambulatory settings where continuous long-term recording is required.