so you see huge loss of gm volume, but not of thickness? What happens to the surface area? And what does "huge" mean in this context? What kind of #s are you seeing, and what kind of means and stds to you see in your controls?
On Tue, 16 Oct 2007, Martin Kavec wrote:
Thanks for the answer, Bruce.
My aim is to assess severity of cortical atrophy and I am trying to find optimal SINGLE parameter for that, i.e. GM thickness, GM volume, or something else.
What I do is, I take mean thickness of a parcel A of a GM from ?h.aparc.stats for the my patient and compare it to the average and STD of thickness of A of my age matched reference group. And the observation is that despite of huge global GM volume loss (computed the same way as above from aseg.stats), thickness of the majority of the cortices in the patient are within the STD of the controls.
On Tuesday 16 October 2007 13:37:40 Bruce Fischl wrote:
Hi Martin,
when you look at the mean difference between this subject and controls
I compare absolute thickness. Initially, I started to look at the (ICV normalized) volume of GM parcel, but there was quite large intersubject variability. Would you recommend me alternative approach (a link)?
you mean it's within a std of the controls? That's not terribly surprising, as there is a lot of normal neuroanatomical variability.
If I understand you correctly, you mean variability of cortical parietal, temporal, frontal, ... thickness within the same subject. This is indeed what I see as well.
Is it below the mean over much of the cortex? Is the overall mean thickness reduced?
I prefer to look at smaller, specific parts of the cortex, the output aparc, because, naturally, severe focal atrophy could get buried in the mean overall thickness.
Thanks,
Martin
cheers, Bruce
On Tue, 16 Oct 2007, Martin Kavec
wrote:
Hi folks,
I have been puzzled for a while with the results from couple of my subjects. They all have clearly visible cerebral atrophy (says neuroradiologist). I ran them through FS-4.0.1 and aseg.stat gives me, as expected, severe loss of gray matter (and others as well) as follows:
GM ICV normalized Age matched reference ICV normalized
What's puzzling me is the cortical thickness. Except of few locations, cortical thickness is within the STD of the controls, and at places it's even thicker. I am wondering, where such a huge GM volume loss (aseg.stats) comes from? Very simplified explanation could be that there is ^3 relation between volume and one of the dimensions of a structure ( V ~ x^3 ). In that case, it would be more sensitive to look at the volume of a parcelated cortical GM. But then, the intersubject variability of the cortical area would come into the play. Is there any other explanation? Is there a single parameter assessing cortical atrophy?
Thanks a lot for the ideas in advance .
Martin
PS.: BTW, what is happening with the OASIS dataset analyzed using FS? When it was released the first time, there were some inconsistencies and it was pulled down from the ftp. _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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