MEG time–frequency analyses for pre- and post-surgical evaluation of patients with epileptic rhythmic fast activity

Sueda, Keitaro; Takeuchi, Fumiya; Shiraishi, Hideaki; Nakane, Shingo; Asahina, Naoko; Kohsaka, Shinobu; Nakama, Hideyuki; Otsuki, Taisuke; Sawamura, Yutaka; Saitoh, Shinji

doi:10.1016/j.eplepsyres.2009.10.002

« Previous Next »Epilepsy Research
Volume 88, Issue 2 , Pages 100-107, February 2010

MEG time–frequency analyses for pre- and post-surgical evaluation of patients with epileptic rhythmic fast activity

Keitaro Sueda
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo, 060-8638, Japan
Fumiya Takeuchi
- Department of Health Science, Hokkaido University School of Medicine, Japan
Hideaki Shiraishi
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo, 060-8638, Japan
Shingo Nakane
- Division of Magnetoencephalography, Hokkaido University Hospital, Japan
Naoko Asahina
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo, 060-8638, Japan
Shinobu Kohsaka
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo, 060-8638, Japan
Hideyuki Nakama
- Department of Neurosurgery, Musashi Hospital, National Center of Neurology and Psychiatry, Japan
Taisuke Otsuki
- Department of Neurosurgery, Musashi Hospital, National Center of Neurology and Psychiatry, Japan
Yutaka Sawamura
- Department of Neurosurgery, Hokkaido University Graduate School of Medicine, Japan
Shinji Saitoh
- Department of Pediatrics, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku, Sapporo, 060-8638, Japan
- Corresponding author. Tel.: +81 11 706 5954; fax: +81 11 706 7898.

Received 4 April 2009; received in revised form 21 September 2009; accepted 4 October 2009.

Summary

Purpose

To evaluate the effectiveness of surgery for epilepsy, we analyzed rhythmic fast activity by magnetoencephalography (MEG) before and after surgery using time–frequency analysis. To assess reliability, the results obtained by pre-surgical MEG and intraoperative electrocorticography were compared.

Methods

Four children with symptomatic localization-related epilepsy caused by circumscribed cortical lesion were examined in the present study using 204-channel helmet-shaped MEG with a sampling rate of 600Hz. One patient had dysembryoplastic neuroepithelial tumor (DNT) and three patients had focal cortical dysplasia (FCD). Aberrant areas were superimposed, to reconstruct 3D MRI images, and illustrated as moving images.

Results

In three patients, short-time Fourier transform (STFT) analyses of MEG showed rhythmic activities just above the lesion with FCD and in the vicinity of DNT. In one patient with FCD in the medial temporal lobe, rhythmic activity appeared in the ipsilateral frontal lobe and temporal lateral aspect. These findings correlate well with the results obtained by intraoperative electrocorticography. After the surgery, three patients were relieved of their seizures, and the area of rhythmic MEG activity disappeared or become smaller. One patient had residual rhythmic MEG activity, and she suffered from seizure relapse.

Conclusion

Time–frequency analyses using STFT successfully depicted MEG rhythmic fast activity, and would provide valuable information for pre- and post-surgical evaluations to define surgical strategies for patients with epilepsy.

Keywords: Magnetoencephalography, Fast activity, Fourier transform, Time–frequency analysis, Symptomatic localization-related epilepsy, Surgical evaluation