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
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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
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