Hello. I am working on a VBM project with some data from a heterogenous psychiatric sample
that was given to me as a part of the master's portion of my graduate training and I've run into a
methodological issue with which I need some assistance.
The full data set is made up of 41 subjects all with behavioral measures of aggression and high
resolution anatomical MR images. 18 subjects have MPRAGE and 23 have SPGR. In my efforts to
learn VBM I started with the MPRAGE subjects and conducted an optimized VBM analysis using Dr.
Gaser's toolbox, but now I am interested in trying to analyze the whole sample together. Of
course my mentors and I realize that having two acquisition sequences is not ideal but I think that
there may be some interesting results and wish to try understand the neural correlates of
aggression in our full sample if we can minimize this error. I am a bit stuck regarding the best
way to preprocess the data from the two acquisition sequences in SPM2. Specifically, I am unsure
whether it would be best to segment and normalize all images (regardless of scan type) to the
same template or to separate templates.
It seems to us that in order to maximize the probability of proper tissue segmentation that it
would be reasonable to create two separate customized templates for each patient group based
on scan type and to segment and normalize each subject to the appropriate templates rather than
to use a single template for all images. Then, once each subject's data are segmented and
normalized, they can all be smoothed and statistically analyzed together, including scan type as a
nuisance variable.
Does this sound like a valid approach? Is there a better way to deal with this issue (other than just
switching to SPM5 or giving up)?
In my searching for an answer in the SPM archives I've been reading a lot about SPM5
segmentation and standard templates being superior to customized templates and negating a
need for the VBM2 "optimized" protocol. The only reason I'm hesitant to switch to SPM5 is because
I am not sure if I can use MARINA to specify custom ROIs in SPM5 - Does anyone know whether or
not this is possible?
Any help will be greatly appreciated.
Sincerely,
Britt Carlson Emerton
Graduate Student in Clinical Psychology and Neuropsychology
Department of Psychology
Suffolk University, Boston, MA
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