Thank you very much Bruce
I have another question: I plan to use permutation testing in order to correct for multiple comparisons. Is it enough to perform 5000 iterations for an initial voxel_wise threshold of 0.005? Is there also any heuristic to select this arbitrary initial threshold and theoretical results for the required number of iterations for the permutations? I appreciate very much your help Jorge Phd Student --- El dom, 29/6/08, Bruce Fischl <[EMAIL PROTECTED]> escribió: > De: Bruce Fischl <[EMAIL PROTECTED]> > Asunto: Re: [Freesurfer] About the area of the vertices in the surfaces > Para: "jorge luis" <[EMAIL PROTECTED]> > CC: freesurfer@nmr.mgh.harvard.edu > Fecha: domingo, 29 junio, 2008 5:22 > Hi Jorge, > > yes, the area of a vertex is 1/3 of the area of all > triangles that it is > a member of, and it should sum to the area of the surface. > The average > subject has a correction factor that accounts for the > "lost" area due to > averaging, so you'll need to apply this if you want it > to be in true mm > (in the average sense across your subjects). mris_info > ~/local_subjects/fsaverage/surf/lh.white > reading group avg surface area 864 cm^2 from file > Reading in average area > /homes/4/fischl/local_subjects/fsaverage/surf/lh.white.avg.area.mgh > SURFACE INFO ======================================== > type : MRIS_TRIANGULAR_SURFACE=MRIS_ICO_SURFACE > num vertices: 163842 > num faces : 327680 > num strips : 0 > surface area: 70394.8 > AvgVtxArea 0.429650 > AvgVtxDist 0.757401 > StdVtxDist 0.227951 > group avg surface area: 86444.7 > . > . > . > > thus, you would need to multiply your areas by > 86444.7/70394.8 to get mm in > the average cross-subject sense. > cheers, > Bruce > > On Sun, 29 Jun > 2008, jorge luis wrote: > > > Hello all > > I have some questions: > > > > I would like to know how freesurfer computes the > vertexÿÿs wise areas? eg. thouse in lh.area. > > > > It should be expected that the sum of the areas of all > the vertices across a surface equals the total surface area? > > > > To be much specific: > > Can I compute the area of an 'activated' > cortical ROI in the average > subject by simply adding the area of all its vertices? > > > > In adavance thank you > > > > Jorge > > Phd Student > > > > > > > > > > > > ¿No te gusta tu dirección de correo? > > Consigue una que te guste de verdad - millones de > direcciones de correo disponibles en Yahoo! > > http://es.docs.yahoo.com/mail/nueva_direccion.html > > > > _______________________________________________ > > Freesurfer mailing list > > Freesurfer@nmr.mgh.harvard.edu > > > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > > > > ______________________________________________ Enviado desde Correo Yahoo! La bandeja de entrada más inteligente. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
