Hi Shahin, it is not as simple as doing a subtraction of the cesvar files. What you are trying to get is the expected variance of your difference between the ces files (as a variance, it must be positive). To get this you need
cesvardiff = (cesvar1+cesvar2)/(2^2)
The 2^2 is the number of inputs (2) squared.
doug
SHAHIN NASR wrote:
Hi,
I have generated two different functional connectivity maps for two different ROI-based seeds. These maps are based on group-average of the same subjects (generated by using separate isxconcat-sess commands ), and now I want to see the difference map. To do so, I used mris_calc as below.
mris_calc -o diff_map/rh.ces.nii map1/rh.ces.nii sub
map2/rh.ces.nii
Also, to generate the rh.cesvar.nii file I used this command:
mris_calc -o diff_map1/rh.cesvar.nii map1/rh.cesvar.nii sub
map2/rh.cesvar.nii
But then when I used the glmfit with WLS option as below:
mri_glmfit --y rh.ces.nii --osgm --glmdir rh.ffx.osgm.wls --nii
--mask ../rh.mask.nii --yffxvar rh.cesvar.nii --ffxdofdat ../ffxdof.dat --surf fsaverage rh --wls rh.cesvar.nii
I faced an error saying: "Error: MRInormWeights: values less than or eq to 0" which I assumed is related to an error in rh.cesvar.nii file (am I right?). Would you tell me how can I fix this problem?
P.S.: please note that sequence of subjects and all MRI parameters are exactly the same between the two maps.
-- Shahin Nasr
PhD in Cognitive Neuroscience Martinos Imaging Center, MGH Harvard Medical School