SPM and DCM experts,
I have a couple questions regarding individual subject VOI creation. After identifying VOIs at the group level, I created a mask for each VOI encompassing a 6mm sphere around the group peak such that when viewing an subject-level contrast within this mask, the global maximum coordinate could be used as the center of an subject's VOI. A script for this is shown below.
matlabbatch{1}.spm.util.voi.spmmat = cellstr(fullfile(data_path,'SPM.mat'));
matlabbatch{1}.spm.util.voi.adjust = 37; % "Effects of Interest - Session 1
matlabbatch{1}.spm.util.voi.session = 1; % session 1
matlabbatch{1}.spm.util.voi.name = 'DCM_THAL_R1';
matlabbatch{1}.spm.util.voi.roi{1}.spm.spmmat = {''}; % using SPM.mat above
matlabbatch{1}.spm.util.voi.roi{1}.spm.contrast = 25;
matlabbatch{1}.spm.util.voi.roi{1}.spm.threshdesc = 'none';
matlabbatch{1}.spm.util.voi.roi{1}.spm.thresh = 0.05;
matlabbatch{1}.spm.util.voi.roi{1}.spm.extent = 0;
matlabbatch{1}.spm.util.voi.roi{2}.mask.image = VOI_MASK
matlabbatch{1}.spm.util.voi.roi{2}.mask.threshold = 0.05;
matlabbatch{1}.spm.util.voi.roi{2}.spm.mask.mtype = 0; % inclusive
matlabbatch{1}.spm.util.voi.roi{3}.sphere.centre = [0 0 0 ];
matlabbatch{1}.spm.util.voi.roi{3}.sphere.radius = 6;
matlabbatch{1}.spm.util.voi.roi{3}.sphere.move.global.spm = 1; % global max
matlabbatch{1}.spm.util.voi.roi{3}.sphere.move.global.mask = 'i2';
matlabbatch{1}.spm.util.voi.expression = 'i1 & i2 &i3';
Then, by duplicating this for each VOI and session (3 sessions total), if no voxels survive for any given VOI, the script would stop and would signal to not use that subject in the following DCM analyses.
I performed this for my group of subjects (n=30), only in 8 subjects was there activation within the mask for each region in each session. I realize that a group peak activation does not necessarily indicate subject level activation in the same area, however, this small subject makes me wonder if my process is incorrect or contraindicated in any way.
Does anyone see any possible errors in the above code or know of other efficient ways to speed up subject-level VOI creation?
Additionally, if the subject-level global maximum within the region mask is identified and is on the boarder of the mask, will the VOI drawn around this point include voxels within a 6mm sphere around the max (specifically those outside of the mask)?
Many thanks,
Drew
