[Freesurfer] Repost: estimating lesion size on surface

Hello,

I just wanted to repost this to see if anyone had any thoughts on an appropriate 'lesion' size for a pothole analysis performed on the surface. We want to compare the average number of small surface lesions (estimated from cortical thickness) across single subjects for a control group relative to our patient group.

We have done similar analyses in the volume for white matter, so one thought was to use that same lesion size. However, that requires estimating a surface area from our previously used volume.

Any thoughts on how to approach this, or thoughts on an appropriate lesion size to use would be appreciated.

Thanks,

-Tim

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Message: 3 Date: Thu, 30 Oct 2014 15:03:53 -0500 From: Timothy Meier tmeier@mrn.org Subject: [Freesurfer] Converting lesion volume to surface area To: freesurfer@nmr.mgh.harvard.edu Message-ID: <CAGXOw+14YO4VBWUAA4YfzE7Gerxo-PG33FPCEmpm8PxpTpW= CA@mail.gmail.com> Content-Type: text/plain; charset="utf-8"

Hello,

Previously we have used a lesion of 128 microliters and have filtered out anything smaller in volume than that for analyses (single subject "pothole" analysis). Now we want to do something similar on the surface. So we need to approximate the surface area of that 128 microliters when translated to group analysis surface (fsaverage).

128 microliters is 128 data points in 1x1x1 resolution. Let's say those data points only exist in the cortical ribbon volume.

Question 1: How many of the 128 data points from cortical ribbon volume get translated into surface space? What is the volume to surface translation ratio?

Question 2: Because we want to filter clusters with mri_surfcluster, we are interested in the resulting area of our original 128 lesion. Therefore, how much area is represented by each data point when translated onto the surface?

Is this simply "AvgVtxArea" of the inflated surface multiplied by the number of data points that get translated from volume to surface?

And what is the best way to answer these two questions from standard Freesurfer output: e.g. Should we calculate from the ("NumVert" "SurfArea" "GrayVol") columns of the lh.aparc.stats file, get the mean of all SurfArea/GrayVol from aparc.stats, and then multiple by our 128?

Any thoughts or suggestions would be appreciated.

Thanks, Tim