Hi,
I am doing a VBM type analysis with FA maps between two groups using 2sample
t-test in SPM2. I am interested in calculating the FA values in the
unnormalised FA maps in those clusters where significant difference between
groups were found in the standard space. I am not sure as to how to do this
but I have tried doing the following:
1. I do 'VOI' using spm2 by drawing spheres of 4 mm radius at the peak of
the cluster of interest.
2. This gives me the voxels in the VOI in mm co-ordinates.
3. Then I use get_orig_coord; which gives me the VOI coordinate in the
unnormalised space in voxel coordinate. (For some reason I get only voxel
coordinate and not mm coordinate)
4. Inorder to convert the voxel coordinate to mm coordinate I use
spm_get_space('unnormalised_image', M)
The matrix M is probably the transformation matrix from voxel to mm
cooordinate. The M matrix is of dim 4x4 and the voxel coordinate vector I
have is nx3 (n = number of voxels in the sphere) and since the dimensions do
not match I am not sure how to do this conversion from voxel to mm
coordinate. I am stuck and not sure how to proceed.
However, my main aim is to get maen FA value for the VOI in the unnormalised
images. Any help would be greatly appreciated.
Anusha
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