?
Hi Freesurfer experts
I have an ultimate goal of performing direct LH v RH comparisons using the fsaverage_sym template, so these pre-analysis steps are aiming to assess the symmetry of the template.
I have performed a first-level fMRI analysis on a subject and am using this to compare the output with the exact same analysis performed on the same subject with LR-flipped data (anatomical, BOLD runs and B0 maps). I then ran recon-all on this flipped subject (treating flipped subject as new subject).
Attached is a screenshot showing the different analysis outputs.
In the top left image, analyses have been performed and smoothed on fsaverage_sym (RH shows LH flipped anat and BOLD data). As you can see, agreement is generally high, but there are also marked differences, most notably in postcentral/precentral regions.
The bottom left shows this output resampled onto the individual surface (for comparison purposes for the next analysis).
The top right image shows the output when analyses were performed on the individual surfaces of the original and flipped subject. Here, agreement seems much higher, also in postcentral/precentral regions (although still not symmetrical). The bottom right image shows this output resampled onto fsaverage_sym, and agreement remains very high.
So it seems that performing the analysis on fsaverage_sym itself may be affecting the expected symmetry of the output. Originally I aimed to perform a comparison of the vectors of B-values in order to prove symmetry, although I am not sure whether this is a viable option anymore. Do you have any advice as to how I could proceed with this?
Finally, it appears that also in the fsaverage_sym template the L/R vertices do not correspond to one another. So will it be possible to flip the analysis values and template in order to perform LH v RH comparisons at the group level?
System: Linux CentOS 6 x86_64 (64b) stable v5.3.0
Thank you for your time
James
