Subject: |  | Re: Conjunction analysis using SPM2 |
From: | | [log in to unmask][log in to unmask]> To: [log in to unmask] Sent: Tuesday, June 5, 2007 5:43:13 AM Subject: [SPM] Total intracranial volume: for information Hi ! As expected in our previous post we have performed some tests to assess the effect of different threshold methods and values on total intracranial volume estimation from segmented and modulated MRI data sets. We have used either different thresholds (from 0 = no threshold, to 0.9) applied on each of the brain partition, or differently thresholded wholebrain masks (again using thresholds from 0 to 0.9). We thus calculated the total intracranial volume of 19 healthy controls and 28 slightly atrophied patients in these 9*9 conditions, and assessed their inter-correlations. As expected, all values were significantly correlated. Highest correlations (r>0.97) were observed for thresholds from 0 to 0.5 (where TIV values decrease from 0 to 35%, respectively). Thresholds above this value lead to decreased correlations (0.95 < r < 0.70) and more than 49% decrease of the maximum TIV value. We thus conclude from this preliminary analysis that the use of <0.5 threshold values would lead to more consistent TIV estimation, and this threshold could be indifferently applied to either each brain partition or the whole brain image. Best regards, Katell ****************************************** Katell MEVEL Doctorante email : [log in to unmask] Tél : +33 (0)2 31 47 02 32 Neuropsychologie Cognitive et Neuroanatomie Fonctionnelle de la Mémoire Humaine Equipe INSERM EMI0218 - EPHE- Université de Caen Basse normandie Laboratoire de Cycéron Blvd Becquerel BP 5229 14074 Caen cedex 5 Tél : +33 (0)2 31 47 02 32 Fax : +33 (0)2 31 47 02 75 ************************************************39_5Jun200705:20:[log in to unmask] |
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Date: | | Sat, 2 Jun 2007 19:59:43 +0100 |
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Hi Ada,
> Dear SPM experts,
> I would like to know the steps for doing a conjunction analysis. I am new to
> this analysis method. After reading those relevant information from the
> archives, I still got a few questions.
> First, Iet me briefly introduce my study design here.
> I have two groups of subject, group A and group B.
> For each subject, I did three contrasts: contrast a = condition 2 >
> condition 1, contrast b = condition 3 > condition 1, and contrast c =
> condition 4 > condition 1.
ok I'll assume cond1 is baseline
> For each of the above contrasts, I performed a contrast on group A > group B
> using two sample t test to look for differences in activation between the
> two groups in each of the contrasts a, b and c.
> I like to do a conjucntion analysis on all the three contrasts (contrasts a,
> b and c) of the A > B contrast.
well I would not call me an SPM expert but I can try to answer -
what I would do is to perform an ANOVA analysis. Since you have 2 groups do not
choose the repeated measure (in SPM5 it is more flexible but as you used SPM2)
- you\ll prob decrease a bit the power but it better than saying it reapeated
measure when it\s not .. anyway let say you now have your ANOVA with 6
conditions gp1a gp1b gp1c gp2a gp2 b and gp2c - you could perform the analyses
you want like [1 1 1 -1 -1 -1] which will show areas different betwen groups on
the whole (pooling conditions) or perform 3 separate contrast gp1>2 like [1 0 0
-1 0 0], [0 1 0 0 -1 0] and [0 0 1 0 0 -1] and finally conjoin them - note that
you can also anaze here interactions like [1 -1 0 -1 1 0] = is the diff a>b in
gp1 different i gp2 ..
hope this helps
cyril
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