title: Co-localization between the BOLD response and epileptiform discharges recorded by simultaneous intracranial EEG-fMRI at 3 T.
abstract: OBJECTIVE
  Simultaneous scalp EEG-fMRI can identify hemodynamic changes associated with the generation of interictal epileptiform discharges (IEDs), and it has the potential of becoming a standard, non-invasive technique for pre-surgical assessment of patients with medically intractable epilepsy. This study was designed to assess the BOLD response to focal IEDs recorded via simultaneous intracranial EEG-functional MRI (iEEG-fMRI).
  
  
  METHODS
  Twelve consecutive patients undergoing intracranial video EEG monitoring were recruited for iEEG-fMRI studies at 3 T. Depth, subdural strip, or grid electrodes were implanted according to our standard clinical protocol. Subjects underwent 10-60 min of continuous iEEG-fMRI scanning. IEDs were marked, and the most statistically significant clusters of BOLD signal were identified (Z-score 2.3, p value < 0.05). We assessed the concordance between the locations of the BOLD response and the IED. Concordance was defined as a distance <1.0 cm between the IED and BOLD response location. Negative BOLD responses were not studied in this project.
  
  
  RESULTS
  Nine patients (7 females) with a mean age of 31 years (range 22-56) had 11 different types of IEDs during fMR scanning. The IEDs were divided based on the location of the active electrode contact into mesial temporal, lateral temporal, and extra-temporal. Seven (5 left) mesial temporal IED types were recorded in 5 patients (110-2092 IEDs per spike location). Six of these IEDs had concordant BOLD response in the ipsilateral mesial temporal structures, <1 cm from the most active contact. One of the two subjects with left lateral temporal IEDs had BOLD responses concordant with the location of the most active contact, as well other ipsilateral and contralateral sites. Notably, the remaining two subjects with extratemporal discharges showed no BOLD signal near the active electrode contact.
  
  
  CONCLUSIONS
  iEEG-fMRI is a feasible and low-risk method for assessment of hemodynamic changes of very focal IEDs that may not be recorded by scalp EEG. A high concordance rate between the location of the BOLD response and IEDs was seen for mesial temporal (6/7) IEDs. Significant BOLD activation was also seen in areas distant from the active electrode and these sites exhibited maximal BOLD activation in the majority of cases. This implies that iEEG-fMRI may further describe the areas involved in the generation of IEDs beyond the vicinity of the electrode(s).
authors.affiliation: Department of Clinical Neurosciences, University of Calgary.
authors.forename: Yahya
authors.initials: Y
authors.lastname: Aghakhani
authors.affiliation: Department of Clinical Neurosciences, University of Calgary ; Hotchkiss Brain Institute, University of Calgary, Canada ; Seaman Family MR Research Centre, University of Calgary, Canada.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Beers
authors.affiliation: Department of Clinical Neurosciences, University of Calgary ; Hotchkiss Brain Institute, University of Calgary, Canada ; Seaman Family MR Research Centre, University of Calgary, Canada.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Pittman
authors.affiliation: Department of Clinical Neurosciences, University of Calgary ; Hotchkiss Brain Institute, University of Calgary, Canada ; Seaman Family MR Research Centre, University of Calgary, Canada.
authors.forename: Ismael
authors.initials: I
authors.lastname: Gaxiola-Valdez
authors.affiliation: Department of Clinical Neurosciences, University of Calgary ; Hotchkiss Brain Institute, University of Calgary, Canada ; Seaman Family MR Research Centre, University of Calgary, Canada ; Department of Psychiatry, University of Calgary, Canada ; Department of Radiology, University of Calgary, Canada.
authors.forename: Bradley G
authors.initials: BG
authors.lastname: Goodyear
authors.affiliation: Department of Clinical Neurosciences, University of Calgary ; Hotchkiss Brain Institute, University of Calgary, Canada ; Seaman Family MR Research Centre, University of Calgary, Canada ; Department of Radiology, University of Calgary, Canada.
authors.forename: Paolo
authors.initials: P
authors.lastname: Federico
mesh_terms: D000328:Adult; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: BOLD response; EEG-fMRI; Epileptiform discharge; IED, interictal epileptiform discharge; VEM, video-EEG monitoring.; intracranial EEG
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