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Hello,

I have a set of 12 coronal slices of BOLD fMRI (covering the frontal lobes
and extending posteriorly to the motor cortex). The Anterior Commissure (AC)
point is centered at Slice #7. I am trying to transform these images into
Tailarach space using spm (part of MEDx 3.0). 

I am running into problems with the final position of the AC point
("origin") of my spatially normalized images. Even if I define the outbox
boundaries accordingly with y dimensions extending the equivalent of 12
slices and centered around AC point, I find that after the images are
normalized, the AC point is consistently shifted posteriorly 16 mm from
where I had set it prior to normalization. What were coronal slices
(acquired 90 degrees to the AC PC line) are now looking diagonal (tilted
forward). The dimensions defined by the boundary box are correct.

 
Has someone encountered such a problem, or should I assume that since the
initial data does not cover the whole brain, then I should not expect an
exact transformation? 

How to explain the tilting forward (a rotation of 15-20 degrees around the X
axis)? I suspect that this is what is making the final AC point seems more
posterior.
Should I try to modify the Number Basis X (or X, or Z) Functions ? Several
different combinations did not seems to make much difference.
Or is the problem with Affine Parameters and Transforms?

Any comments would be greatly appreciated.

Thank you in advance
ZN

Ziad Nahas, MD
Medical Director, Brain Stimulation Laboratory
Functional Neuroimaging Division
Medical University of South Carolina



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