Thanks, Doug! So I tried this method using fsaverage/surf/lh.white.avg.area.mgh. The results seem to be reasonably consistent with the ones I get when eyeballing the p-maps overlayed on fsaverage in tksurfer. Would you agree that's a reasonable "sanity check"?
When I compare the results to just counting vertices, there doesn't seem to be a huge difference between proportion of #vertices and proportion of surface area. So either there isn't a lot of variance in the sizes of the faces, or the variance is evenly distributed. Finally, if I want to convert from an individual map or the cohort mean map to mm² units, can I do it by scaling the ico area vertex values by the ratio between native and ico total area? So: (vertex value from mean cohort map * total area for cohort mean map) / total area for fsaverage/surf/lh.white.avg.area.mgh, where total area would be the sum of all vertex values? Thank you! LMR ------------------------------------------------------------------------------------------------------- You don't want to get the surface area from the faces of fsaverage. Instead use the values in fsaverage/surf/lh.white.avg.area.mgh (this is the average of the group used to create fsaverage), or, probably better, get an average area map for your cohort doug On 07/30/2014 08:38 AM, Lars M. Rimol wrote: > Hi Bruce, > > I would like to be able to tell what proportion of a region of > interest (ROI), as defined in atlas space by e.g. Desikan-Killiany, > that shows a significant effect (based on a p-map). For now I overlay > the p-map on the inflated surface of fsaverage in tksurfer and eyeball > the proportion. > > Given a p-map, if I find the FDR threshold and identify the vertices > within a given ROI that have a p-value greater than the threshold, > then I can find the proportion of the ROI that is suprathreshold. > E.g., I find 1986 suprathreshold vertices in "bankssts" out of 2137, > so 93% of vertices in bankssts show a significant effect. > > My question is: Does that tell me anything about what proportion of > the ROI's surface area is affected in atlas space? Obviously, if the > faces were uniform, there would be a 1 to 1 relationship between > #vertices and area. In the original tesselation of any dataset the > size of the faces is uniform, but that changes with topology fix and > deformation. I assume that is true also for fsaverage? (so I can't > assume [#sig vertices] / [# tot vertices] == the proportion of the > ROI's area that is significant in atlas space) > > I can find the surface area of the suprathreshold region for my sample > (or any subset thereof) by looking at a mean area map. But I'm unsure > how to do that for fsaverage itself? Is there information on regional > surface area directly available? Or would using getFaceArea.m or > getFacesArea.m or similar functions be a solution? > > > Thank you! -- yours, Lars M. Rimol, PhD St. Olavs Hospital Trondheim, Norway
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