Am 24.02.12 17:38, schrieb Kairys, Anson:
> Thanks for the response.
> I ran my analysis, One concern is that I am seeing decreases in the border between occipital lobe and cerebellum. It appears to me that this is one of those regions that is difficult to segment correctly, therefore I may mask it out. Do you think this is appropriate? It just looks like one of those clusters that is a little questionable that I encounter occasionally when doing VBM.
If the region is difficult to segment it might be allowed to masked it out, but there is always some kind of arbitrariness. A better way might be to additionally use a larger extent threshold to get rid of these small effects.
Christian Gaser, Ph.D.
Departments of Psychiatry and Neurology
Friedrich-Schiller-University of Jena
Jahnstrasse 3, D-07743 Jena, Germany
Tel: ++49-3641-934752 Fax: ++49-3641-934755
e-mail: [log in to unmask]
> Anson K.
> -----Original Message-----
> From: Christian Gaser [mailto:[log in to unmask]]
> Sent: Friday, February 24, 2012 11:35 AM
> To: [log in to unmask]; Kairys, Anson
> Cc: Christian Gaser
> Subject: Re: Longitudinal VBM8 Toolbox
> Hi Anson,
> On Fri, 17 Feb 2012 15:27:57 +0000, Anson Kairys<[log in to unmask]> wrote:
>> Hi All,
>> I just finished going through the workflow for the VBM8 longitudinal analysis.
>> I am wondering if these images are modulated or not (i.e. volume or concentration). If they are, can I produce un-modulated images in order to assess Gm concentration, using this very useful automated longitudinal procedure? Or would I need to use the basic approach?
> There is no modulation applied to the longitudinal images, because the spatial normalization parameters (= inverse modulation) is the same for all time points of one subject. Thus, you will rather analyze absolute GM differences between the time points than relative differences. There was an discussion about the impact of modulating longitudinal data or not, but my experience is that the modulation is not necessary because it will be the same for all time points.
> Christian Gaser, Ph.D.
> Departments of Psychiatry and Neurology
> Friedrich-Schiller-University of Jena
> Jahnstrasse 3, D-07743 Jena, Germany
> Tel: ++49-3641-934752 Fax: ++49-3641-934755
> e-mail: [log in to unmask]
>> thanks for all the great help
>> Anson K.
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