Modeling of post-surgical brain and skull defects in the EEG inverse problem with the boundary element method.
OBJECTIVE
In order to obtain accurate EEG inverse solutions in patients subjected to surgery, we have studied the feasibility and influence of incorporating brain and skull defects in realistic head models.


METHODS
We first measured the conductivity of the methacrylate used for cranioplasty. Then, we designed realistic boundary element method head models with a skull burr hole, a methacrylate plug or a temporal-lobe resection. We simulated the potentials that would be produced at 71 electrode locations (10/10 system) by dipoles located near the defects. Then, we fitted dipoles on these potentials using a defect-free head model. We also ran simulations in a noisy situation and with higher skull and cerebrospinal fluid (CSF) conductivity.


RESULTS
The largest errors were found for burr holes, with a localization error up to 20 mm for a radial dipole located 30 mm below the hole and an amplification factor of 8. Methacrylate plugs lead to errors up to 5 mm and 0.5; the resection only lead to errors of 2 mm and 1.3. Results obtained with noise were consistent with those obtained without noise. Doubling the skull conductivity led to errors that were reduced by 10-20%, while doubling CSF conductivity increased the errors by up to 31%.


CONCLUSIONS
We have shown that it is important to incorporate skull defects in realistic head models when sources are located near the defects and precision is sought. Brain cavities of the size of a typical anterior temporal lobe resection may be omitted without a significant impact on dipole localization.
Bénar
C G
CG
Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Quebec, Canada H3A 2B4.
Gotman
J
J
D001921:Brain / Q000473:pathology* / Q000601:surgery; D002555:Cerebrospinal Fluid / Q000502:physiology; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D004553:Electric Conductivity; D004569:Electroencephalography; D006801:Humans; D008689:Methacrylates; D008953:Models, Anatomic; D008959:Models, Neurological; D019635:Neurosurgical Procedures; D011184:Postoperative Period; D019279:Resin Cements; D012886:Skull / Q000473:pathology*
D008689:Methacrylates; D019279:Resin Cements