title: MEG time-frequency analyses for pre- and post-surgical evaluation of patients with epileptic rhythmic fast activity.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Pediatrics, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo, Japan.
authors.forename: Keitaro
authors.initials: K
authors.lastname: Sueda
authors.forename: Fumiya
authors.initials: F
authors.lastname: Takeuchi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Shiraishi
authors.forename: Shingo
authors.initials: S
authors.lastname: Nakane
authors.forename: Naoko
authors.initials: N
authors.lastname: Asahina
authors.forename: Shinobu
authors.initials: S
authors.lastname: Kohsaka
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Nakama
authors.forename: Taisuke
authors.initials: T
authors.lastname: Otsuki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Sawamura
authors.forename: Shinji
authors.initials: S
authors.lastname: Saitoh
mesh_terms: D001931:Brain Mapping; D002540:Cerebral Cortex / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D002648:Child; D004569:Electroencephalography; D004828:Epilepsies, Partial / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D011877:Radionuclide Imaging; D016896:Treatment Outcome