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
