title: 3D visualization of subdural electrode shift as measured at craniotomy reopening.
abstract: OBJECTIVE
  Subdural electrodes are implanted for recording intracranial EEG (iEEG) in cases of medically refractory epilepsy as a means to locate cortical regions of seizure onset amenable to surgical resection. Without the aid of imaging-derived 3D electrode models for surgical planning, surgeons have relied on electrodes remaining stationary from the time between placement and follow-up resection. This study quantifies electrode shift with respect to the cortical surface occurring between electrode placement and subsequent reopening.
  
  
  METHODS
  CT and structural MRI data were gathered following electrode placement on 10 patients undergoing surgical epilepsy treatment. MRI data were used to create patient specific post-grid 3D reconstructions of cortex, while CT data were co-registered to the MRI and thresholded to reveal electrodes only. At the time of resective surgery, the craniotomy was reopened and electrode positions were determined using intraoperative navigational equipment. Changes in position were then calculated between CT coordinates and intraoperative electrode coordinates.
  
  
  RESULTS
  Five out of ten patients showed statistically significant overall magnitude differences in electrode positions (mean: 7.2mm), while 4 exhibited significant decompression based shift (mean: 4.7mm), and 3 showed significant shear displacement along the surface of the brain (mean: 7.1mm).
  
  
  CONCLUSIONS
  Shift in electrode position with respect to the cortical surface has never been precisely measured. We show that in 50% of our cases statistically significant shift occurred. These observations demonstrate the potential utility of complimenting electrode position measures at the reopening of the craniotomy with 3D electrode and brain surface models derived from post-implantation CT and MR imaging for better definition of surgical boundaries.
authors.affiliation: Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA. plaviole@mcw.edu
authors.forename: Peter S
authors.initials: PS
authors.lastname: LaViolette
authors.forename: Scott D
authors.initials: SD
authors.lastname: Rand
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Ellingson
authors.forename: Manoj
authors.initials: M
authors.lastname: Raghavan
authors.forename: Sean M
authors.initials: SM
authors.lastname: Lew
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Schmainda
authors.forename: Wade
authors.initials: W
authors.lastname: Mueller
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D003399:Craniotomy / Q000379:methods; D004567:Electrodes, Implanted / Q000009:adverse effects; D004569:Electroencephalography / Q000379:methods; D004827:Epilepsy / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D013355:Subdural Space / Q000473:pathology* / Q000601:surgery*; D014057:Tomography, X-Ray Computed / Q000379:methods; D055815:Young Adult