title: Recording temporal lobe epileptic activity with MEG in a light-weight magnetic shield.
abstract: OBJECTIVE
  To assess the interictal epileptic discharges (IEDs) detection rate of magnetoencephalography (MEG) recordings performed in a new light-weight magnetic shielding (LMSR) concept in a large group of consecutive patients with presumed mesiotemporal lobe epilepsy (MTLE).
  
  
  METHODS
  Thirty-eight patients (23 women; age range: 6-63 years) with presumed MTLE were prospectively studied. MEG investigations were performed with the 306-channel Elekta Neuromag® MEG-system installed in a normal hospital environment into a LMSR (MaxShield, Elekta Oy). Equivalent current dipoles (ECD, g/% > 80%) corresponding to epileptic events were fitted to each patient's spherical head model at IEDs onset and peak and then superimposed on the patient's co-registered MRI.
  
  
  RESULTS
  IEDs were observed in 26 out of 38 patients (68.4%). Temporal ECDs were mesial in 14 patients, anterior in 23 patients and posterior in 8 patients. Interestingly, in 6 patients, ECDs fitted at spike-onset were localized in the hippocampus while at the peak of the spike, they had an anterior temporal location.
  
  
  CONCLUSIONS
  MEG using LMSR provides adequate signal to noise ratio (SNR) to allow reliable detection and localization of single epileptic abnormalities on continuous MEG data in 68% of patients with presumed MTLE. Moreover, mesial temporal epileptic sources were detected in 54% of patients with abnormal MEG. The SNR of MEG data acquired using the LMSR is therefore suitable for the non-invasive localization of epileptic foci in patients with MTLE. The use of LMSR, which are cheaper and smaller than conventional MSR, should facilitate the development of MEG in clinical environments.
authors.affiliation: Reference Centre for Refractory Epilepsy, Ghent University Hospital, Ghent, Belgium.
authors.forename: Evelien
authors.initials: E
authors.lastname: Carrette
authors.forename: Marc
authors.initials: M
authors.lastname: Op de Beeck
authors.forename: Mathieu
authors.initials: M
authors.lastname: Bourguignon
authors.forename: Paul
authors.initials: P
authors.lastname: Boon
authors.forename: Kristl
authors.initials: K
authors.lastname: Vonck
authors.forename: Benjamin
authors.initials: B
authors.lastname: Legros
authors.forename: Serge
authors.initials: S
authors.lastname: Goldman
authors.forename: Patrick
authors.initials: P
authors.lastname: Van Bogaert
authors.forename: Xavier
authors.initials: X
authors.lastname: De Tiège
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004569:Electroencephalography / Q000295:instrumentation / Q000379:methods; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D055815:Young Adult