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Dear Gregor, The idea behing BEM is that the model consists in nested volumes with uniform and isotropic conductivities. A thin CSF volume could have been included between the "brain volume" and "skull volume" but wasn't because - at the time that CSF layer was difficult to extract from sMRI - its influence would be relatively small given the high conductivity of CSF in a thin layer around the brain volume - it could have lead to numerical errors given the thinness of that compartment - time would have been better spent including the ventricles or other bits of the head in the model. Best, Chris Le 20/01/2012 21:10, Vladimir Litvak a écrit : > Yes, brain and CSF is the same thing for this particular purpose. You > can get more technical details from Christophe (CCed) who wrote the > BEM code. > > Best, > > Vladimir > > On Fri, Jan 20, 2012 at 6:31 PM, Gregor Strobbe > <[log in to unmask] <mailto:[log in to unmask]>> wrote: > > Thank you for your answer, > > I assume the CSF isn't modeled, just one brain compartment with > one conductivity value? > > I am asking this, because I want to build exactly the same model > based on the Finite Difference Method to compare with BEM as a > first comparison step. The next step is to compare with more > advanced FDM head models. > > Kind regards > > > 2012/1/20 Vladimir Litvak <[log in to unmask] > <mailto:[log in to unmask]>> > > Dear Gregor, > > What matters for the BEM computation is the inner skull > boundary which separates the bone compartment from the CSF > compartment. The brain surface is only used to create the > source model for imaging source reconstruction i.e. figure out > where the dipoles are located and how they are oriented. If > you just want to put a dipole somewhere inside the head and > compute its lead field you don't need the cortical surface for > that. I hope this helps. > > Best, > > Vladimir > > > On Fri, Jan 20, 2012 at 3:03 PM, Gregor Strobbe > <[log in to unmask] <mailto:[log in to unmask]>> wrote: > > Dear SPM experts, > > I have a question about the bemcp method to build a BEM > model for EEG source reconstruction in SPM. Am I right > that there are three different tissues assumed in the > model, including scalp, skull and brain tissue? Can > someone explain me, how the cortical surface is > incorporated in this model? Is the cortical surface > explicitly incorporated in the calculation of the BEM lead > fields? > > Kind regards > > Gregor > > -- > > Gregor Strobbe > > Doctoral researcher > IBiTech - Medisip (Ghent University) > De Pintelaan 185, Blok B > BE-9000 Gent (Belgium) > Tel: +3293324322 <tel:%2B3293324322> > http://medisip.elis.ugent.be/ > > > > > > -- > > Gregor Strobbe > > Doctoral researcher > IBiTech - Medisip (Ghent University) > De Pintelaan 185, Blok B > BE-9000 Gent (Belgium) > Tel: +3293324322 <tel:%2B3293324322> > http://medisip.elis.ugent.be/ > >