Dear ML,
If you apply a standard ROI set on images which are all in register in MNI space, all your subjects will have exactly the same regional volume and you will be none the wiser.
Two crude fixes around it:
- multiply with their GM contribution, as for example in Edison P et al. 2007 for PET
- back-normalise your ROI set to individual space via the parameters derived from the spatial normalisation, e.g. Hammers A et al. 2002
However, it would be better to segment the individual MRIs in native space (see Heckemann RA et al. Neuroimage 2006). You can do this with multiple individual atlases (e.g. Hammers A, Allom R et al. 2003, Gousias IS et al. 2008 - atlases available via
www.brain-development.org) and individual registrations; given the patients have epilepsy and therefore likely some abnormal anatomy (e.g. Hammers A et al. 2007) it would probably be best to account for this via e.g. MAPER (Heckemann RA et al. Neuroimage 2010).
Hope this helps!
All the best,
Alexander
-----------------------------------------
Alexander Hammers, MD PhD
Professor (Honorary Consultant) of Imaging and Neuroscience
Head of PET Imaging Centre
Division of Imaging Sciences and Biomedical Engineering
King's College London
St Thomas' Hospital, London
Telephone
+44-(0)20 7188 8364 (PA Viviane Schroeder)
Email
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Dear SPM experts,
I am doing a study on correlation between specific regional brain volume and epilepsy. The MRI scans provided are structural.
The steps i have taken to process the images are set origin to AC->realign->coregister->segment->create DARTEL template->normalize to MNI space, before i create a ROI mask to quantify the volume. In the coregister step, i have coregister my structural images to the mean image output from the realignment steps. I understand that coregister is not necessary unless you want to 'merge' functional images to the structural images (please correct me if i'm wrong).
I would like to check if there is any implication in the final volume that i have calculated, by doing the additional coregister steps.
I would also like to check if the steps i have taken to quantify the volume is correct.
Thank you very much for the help
Regards,
ML