Hi Antonios-Konstantinos,
as far as I can tell, AD has produced so far the strongest changes seen in VBM, even early in disease onset, so really I would not be surprised...
You might want to add the grey matter volume after affine registration (=modulated grey matter volume after non-linear registration) for each subject as a covariate to see where GM loss is "accelerated" in the patients.
I can have a look at your data if you're still unsure. If so, please upload them and give me the upload number.
Cheers,
Gwenaelle
--- En date de : Jeu 7.5.09, Antonios-Konstantinos Thanellas <[log in to unmask]> a écrit :
> De: Antonios-Konstantinos Thanellas <[log in to unmask]>
> Objet: [FSL] VBM analysis went wrong
> À: [log in to unmask]
> Date: Jeudi 7 Mai 2009, 15h26
> Dear fsl users,
>
> I have a dataset consisting of 2 groups of subjects (31
> Controls- 17
> Alzheimer's patients). The Alzheimer's dataset
> consists of T1 scans that
> were taken 6 months after the "onset" of the
> disease. I did VBM analysis
> using a kernel of 3 cause I was expecting small to
> intermediate changes
> (since my scans depict an early stage of the disease) and
> after
> fslvbm_3_proc, 4 volumes out of 48 were distorted. I
> excluded these 4 vols
> from the GM_mod_merg_s3 files and continued with randomise
> choosing a
> threshold of 3 for cluster size and cluster mass tests.
> Though my results
> (tfce_corrp_tstat,clustere_corrp_tstat and
> clusterm_corrp_tstat) were really
> strange revealing huge clusters covering 60-70% of the
> whole brain with very
> high p-values < 0.003. It's not logical to expect
> such severe changes and I
> cannot point out what went wrong in the analysis.
> I would really appreciate your help.
> Antonios-Konstantinos Thanellas
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