Usefulness of multiple frequency band source localizations in ictal MEG

Jeong, Woorim; Kim, June Sic; Chung, Chun Kee

doi:10.1016/j.clinph.2015.07.015

Cited by 12 publications

(13 citation statements)

References 36 publications

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“…However, previous studies had used either a manual selection of a particular period distinct from the BGA 36 or a wide time window. 7 The present study selected a 4-second ictal window and computed non-time-resolved frequency analysis, to circumvent the subjective bias of time window selection. This approach increases the SNR and improves the localization accuracy.…”

Section: Source Localization With Beamformermentioning

confidence: 99%

“…5 However, ictal MEG data are rare, and very limited reports are available, studied on small cohorts. Previous studies had analyzed ictal MEG data in lower frequency bandwidth (<45 Hz), 6 except in a study 7 that reported multiple frequency band analysis up to gamma band (<70 Hz). None of the studies had evaluated ictal the MEG record for high-frequency oscillations (HFOs).…”

Section: Introductionmentioning

confidence: 99%

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Magnetoencephalographic imaging of ictal high‐frequency oscillations (80‐200 Hz) in pharmacologically resistant focal epilepsy

et al. 2017

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SummaryObjective: Specificity of ictal high-frequency oscillations (HFOs) in identifying epileptogenic abnormality is significant, compared to the spikes and interictal HFOs. The objectives of the study were to detect and to localize ictal HFOs by magnetoencephalography (MEG) for identifying the seizure onset zone (SOZ), evaluate the cortical excitability from preictal to ictal transition, and establish HFO concordance rates with other modalities and postsurgical resection. Methods: Sixty-seven patients with drug-resistant epilepsy had at least 1 spontaneous seizure each during MEG acquisition, and analysis was carried out on 20 seizures from 20 patients. Ictal MEG data were bandpass filtered (80-200 Hz) to visualize, review, and analyze the HFOs co-occurring with ictal spikes. Source montages were generated on both hemispheres, mean fast Fourier transform was computed on virtual time series for determining the preictal to ictal spectral power transition, and source reconstruction was performed with sLORETA and beamformers. The concordance rates of ictal MEG HFOs (SOZ) was estimated with 4 reference epileptogenic regions. Results: In each subject, transient bursts of high-frequency oscillatory cycles, distinct from the background activity, were observed in the periictal continuum.Time-frequency analysis showed significant spectral power surge (85-160 Hz) during ictal state (P < .05) compared to preictal state, but there was no variation in the peak HFO frequencies (P > .05) for each subgroup and at each source montage. HFO source localization was consistent between algorithms (k = 0.857 AE 0.138), with presumed epileptogenic zone (EZ) comparable to other modalities. In patients who underwent surgery (n = 6), MEG HFO SOZ was concordant with the presumed EZ and the surgical resection site (100%), and all were seizure-free during follow-up. Significance: HFOs could be detected in the MEG periictal state, and its sources were accurately localized. During preictal to ictal transition, HFOs exhibited

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Section: Source Localization With Beamformermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetoencephalographic imaging of ictal high‐frequency oscillations (80‐200 Hz) in pharmacologically resistant focal epilepsy

et al. 2017

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“…Movement compensation [26,52] and the projection of recorded data to a standard virtual MEG helmet [53] enable the correction of (limited) patient movement during a seizure and increases the percentage of usable MEG recordings. Analytically, the application of STFT [27,28,31] for identification of seizure onsets, and the use of distributed source localization approaches [32,34], especially frequency-based methods [31], seem to improve the localization accuracy in comparison to ECD approaches. Regarding MEG ictal focus localization, there is very little data on specific aspect of localization methodology in lesional subgroups.…”

Section: Discussionmentioning

confidence: 99%

“…Even if such problems do not occur, the SNR of ictal activity may be low at the seizure onset, resulting in localization issues. Frequency-based methods, such as STFT [27,28] or multiple-frequency-band source localization [31] may be helpful in such circumstances. Furthermore, general limitations of MEG, such as artifacts due to metal implants, are of course also relevant for ictal recordings.…”

Section: Discussionmentioning

confidence: 99%

“…Jeong et al [31] analyzed data from 13 patients with focal drug-resistant epilepsies, of whom 6 patients had normal magnetic resonance imaging (MRI), and 8 received preoperative invasive evaluation. All patients underwent epilepsy surgery with a mean postoperative follow-up of 3.98 years and had seizure outcomes of International League Againt Epilepsy (ILAE) 1 in 9 patients, and 3-6 in the remainder.…”

Section: Ictal Megmentioning

confidence: 99%

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Interictal and Ictal MEG in presurgical evaluation for epilepsy surgery

Stefan

Rampp

2020

Acta Epileptologica

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Although presurgical evaluation of patients with pharamacoresistent focal epilepsies provides essential information for successful epilepsy surgery, there is still a need for further improvement. Developments of noninvasive electrophysiological recording and analysis techniques offer additional information based on interictal and ictal epileptic activities. In this review, we provide an overview on the application of ictal magnetoencephalography (MEG). The results of a literature research for published interictal/ictal MEG findings and experiences with own cases are demonstrated and discussed. Ictal MEG may provide added value in comparison to interictal recordings. The results may be more focal and closer to the invasively determined seizure onset zone. In some patients without clear interictal findings, ictal MEG could provide correct localization. Novel recording and analysis techniques facilitate ictal recordings. However, extended recording durations, movement and artifacts still represent practical limitations. Ictal MEG may provide added value regarding the localization of the seizure onset zone but depends on the selection of patients and the application of optimal analysis techniques.

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Assessment of the Utility of Ictal Magnetoencephalography in the Localization of the Epileptic Seizure Onset Zone

et al. 2018

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IMPORTANCE Literature on ictal magnetoencephalography (MEG) in clinical practice and the relationship to other modalities is limited because of the brevity of routine studies. OBJECTIVE To investigate the utility and reliability of ictal MEG in the localization of the epileptogenic zone. DESIGN, SETTING, AND PARTICIPANTS A retrospective medical record review and prospective analysis of a novel ictal rhythm analysis method was conducted at a tertiary epilepsy center with a wide base of referrals for epilepsy surgery evaluation and included consecutive cases of patients who experienced epileptic seizures during routine MEG studies from March 2008 to February 2012. A total of 377 studies screened. Data were analyzed from November 2011 to October 2015. MAIN OUTCOMES AND MEASURES Presurgical workup and interictal and ictal MEG data were reviewed. The localizing value of using extended-source localization of a narrow band identified visually at onset was analyzed. RESULTS Of the 44 included patients, the mean (SD) age at the time of recording was 19.3 (14.9) years, and 25 (57%) were male. The mean duration of recording was 51.2 minutes. Seizures were provoked by known triggers in 3 patients and were spontaneous otherwise. Twenty-five patients (57%) had 1 seizure, 6 (14%) had 2, and 13 (30%) had 3 or more. Magnetoencephalography single equivalent current dipole analysis was possible in 29 patients (66%), of whom 8 (28%) had no clear interictal discharges. Sublobar concordance between ictal and interictal dipoles was seen in 18 of 21 patients (86%). Three patients (7%) showed clear ictal MEG patterns without electroencephalography changes. Ictal MEG dipoles correlated with the lobe of onset in 7 of 8 patients (88%) who underwent intracranial electroencephalography evaluations. Reasons for failure to identify ictal dipoles included diffuse or poor dipolar ictal patterns, no MEG changes, and movement artifact. Resection of areas containing a minimum-norm estimate of a narrow band at onset, not single equivalent current dipole, was associated with sustained seizure freedom. CONCLUSIONS AND SIGNIFICANCE Ictal MEG data can provide reliable localization, including in cases that are difficult to localize by other modalities. These findings support the use of extended-source localization for seizures recorded during MEG.

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Usefulness of multiple frequency band source localizations in ictal MEG

Cited by 12 publications

References 36 publications

Magnetoencephalographic imaging of ictal high‐frequency oscillations (80‐200 Hz) in pharmacologically resistant focal epilepsy

Magnetoencephalographic imaging of ictal high‐frequency oscillations (80‐200 Hz) in pharmacologically resistant focal epilepsy

Interictal and Ictal MEG in presurgical evaluation for epilepsy surgery

Assessment of the Utility of Ictal Magnetoencephalography in the Localization of the Epileptic Seizure Onset Zone

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