Hi Oerjan,

yes, but I don't see a way to do that with the longistudinal stream. You could, however, first register surfaces across twin pairs and then go to fsaverage. You could fix cortical parcellations fixed across twin pairs on the target twin and compare ROI values across twins. You could also compute difference in thickness for each twin pair first and then compare across groups on fsaverage.

Yet for all this you'd have to select one of the twins as registration target. This would not bias your data as you can select the target randomly.

Best, Martin


On 11/10/2015 03:58 AM, Örjan de Manzano wrote:
Thank you for the quick reply!
I've been elaborating with a ROI-based approach for VBM where I first create an unbiased template for each MZ-pair (non-linear registration; ANTS SyN); second, create a group template in MNI-space where ROIs are defined; third, warp each pair template to the group template and use the inverse transformations to get ROIs to pair-space where data are obtained (from the modulated images native->pair). With this approach, deformations are smaller and specific to each paired comparison and I do not have to smooth the data as much. From what I can tell, it outperforms the traditional group analysis when using MZ twins. Would it make sense to try something similar with the cortical thickness analysis in Freesurfer?
Best,
Örjan




From: freesurfer-bounces@nmr.mgh.harvard.edu [freesurfer-bounces@nmr.mgh.harvard.edu] on behalf of Martin Reuter [mreuter@nmr.mgh.harvard.edu]
Sent: Wednesday, November 04, 2015 14:55
To: Freesurfer support list
Subject: Re: [Freesurfer] applying longitudinal processing on twins

Hi Oerjan,

yes, MZ twins are very similar (InfoAd: are you familiar with our BrainPrint NeuroImaging paper where we compare MZ and DZ brain shapes: http://www.sciencedirect.com/science/article/pii/S1053811915000476
http://reuter.mit.edu/blue/papers/wachinger-brainprint15/wachinger-brainprint15.pdf  ).

Anyway, I doubt the longitudinal stream is going to work for this, as it is really designed for longitudinal and not across subject situations (even with MZ twins I expect differences to be too large). Even if a few cases work, there will be too many that fail.

Best, Martin



On 11/04/2015 05:13 AM, Örjan de Manzano wrote:
Dear FreeSurfers,

I'm about to analyze cortical thickness in monozygotic twins discordant for certain expertise. The within-pair similarities in brain morphology are striking (e.g. twin1 x twin2 intracranial volume correlation r=.99) and you could easily play a memory game with the images. Nonetheless, there are notable within-pair differences in gyrification etc. I'm trying to figure out if the longitudinal stream, or some version of it, might still be a viable option in this situation. The sample is fairly small and I want to do what I can to maximize sensitivity. Do any of you have experience with a similar data set or ideas/opinions/recommendations?

Best regards,

Örjan


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-- 
Martin Reuter, PhD
Assistant Professor of Radiology, Harvard Medical School
Assistant Professor of Neurology, Harvard Medical School
A.A.Martinos Center for Biomedical Imaging
Massachusetts General Hospital
Research Affiliate, CSAIL, MIT
Phone: +1-617-724-5652
Web  : http://reuter.mit.edu 


_______________________________________________
Freesurfer mailing list
Freesurfer@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer

-- 
Martin Reuter, PhD
Assistant Professor of Radiology, Harvard Medical School
Assistant Professor of Neurology, Harvard Medical School
A.A.Martinos Center for Biomedical Imaging
Massachusetts General Hospital
Research Affiliate, CSAIL, MIT
Phone: +1-617-724-5652
Web  : http://reuter.mit.edu