Cool, thanks! On Tue, Apr 17, 2018 at 6:59 PM, Glasser, Matthew <[email protected]> wrote:
> Hi Amanda, > > wb_command -surface-vertex-areas does this. > > Peace, > > Matt. > > From: <[email protected]> on behalf of Amanda Mejia < > [email protected]> > Date: Tuesday, April 17, 2018 at 5:52 PM > To: Timothy Coalson <[email protected]> > Cc: hcp-users <[email protected]> > Subject: Re: [HCP-Users] cortical surface vertex spacing in 32K > > I see, thanks for clarifying. Is it possible to calculate the total > surface area that each vertex is responsible for, on average? I'm > resampling to a lower resolution and want to be able to report the > before-and-after average vertex "size". I'd be happy to report the average > spacing between vertices after resampling instead, if that can be computed. > > On Tue, Apr 17, 2018 at 5:41 PM, Timothy Coalson <[email protected]> wrote: > >> The average cortical thickness in humans is somewhere around 2.5mm, so >> you don't have multiple layers of voxels, you have barely over 1 layer on >> average, in theory. Diagonals make this more complicated, of course. >> >> The vertices are also not laid out as a grid, they are instead a >> triangular mesh - similar to hexagonal close-packing, this allows more of >> them to fit in a defined surface area with a given distance between them >> than a grid layout (like voxels) would. >> >> As you hint at, the cortical surfaces have spherelike topology, and a >> number of those vertices are in the "medial wall", where the >> single-hemisphere surfaces cut through the corpus callosum. We use just >> under 30k vertices per hemisphere for the cortex itself, out of the 32k >> vertices in the full surface. >> >> Finally, the 2mm spacing is somewhat approximate (it was adjusted >> empirically, not directly controlled), and it is not entirely even across >> the anatomical surfaces - some difference in stretching is inevitable >> because a brain inflates to something more like a football than a sphere, >> and we use fully regular spherical topologies for our current atlases. >> >> Tim >> >> >> On Tue, Apr 17, 2018 at 9:11 AM, Amanda Mejia <[email protected]> >> wrote: >> >>> In the HCP FAQ and several HCP-related publications (e.g., A Multi-modal >>> Parcellation of Human Cerebral Cortex by Glasser et al.), there is a >>> statement about the surface vertices in 32K resolution and the 2mm >>> isotropic voxels being on a "similar scale". The aforementioned paper >>> further states that the average cortical vertex spacing is 2mm. If I'm >>> reading this correctly, this would imply that the average distance in two >>> dimensions between each vertex is similar to the distance between two 2mm >>> voxels in a *single* layer. This would seem to imply that since the >>> cortical ribbon in volumetric space is several voxels thick, each vertex >>> would be equivalent to multiple voxels. But this isn't consistent with the >>> fact that there are a similar number of cortical gray matter 2mm voxels and >>> cortical surface vertices (~60,000 across both hemispheres). It would seem >>> to me that the only way to keep the number of locations the same, while >>> transforming the data from multiple layers (of voxels) to a single layer >>> (of vertices) would be to make the vertices closer together than 2mm. Can >>> someone please clarify? >>> >>> Amanda >>> >>> -- >>> AMANDA F MEJIA, PhD >>> Assistant Professor >>> Department of Statistics >>> Indiana University Bloomington >>> https://mandymejia.wordpress.com/ >>> >>> _______________________________________________ >>> HCP-Users mailing list >>> [email protected] >>> http://lists.humanconnectome.org/mailman/listinfo/hcp-users >>> >> >> > > > -- > AMANDA F MEJIA, PhD > Assistant Professor > Department of Statistics > Indiana University Bloomington > https://mandymejia.wordpress.com/ > > _______________________________________________ > HCP-Users mailing list > [email protected] > http://lists.humanconnectome.org/mailman/listinfo/hcp-users > -- AMANDA F MEJIA, PhD Assistant Professor Department of Statistics Indiana University Bloomington https://mandymejia.wordpress.com/ _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
