Hi,
I have one participant session that will not coregister for me
correctly. I am using the same preprocessing procedure as worked well on
two previous participants, so I don't think there is an error in the
script.
The result I am getting is that the structural image is rolled a little
to the left (~0.05 rad), pitched forward (~.1-.2 rad) and displaced
downwards. Functional realignment is working fine, and I am using the
resulting mean image as the reference.
The things I have tried so far are to make the tolerances smaller, to
move the origin in the structural image on to the AC (using the Display
function), to approximately align the functional and structural images
by hand (with Check Reg), and combinations of these. But always when I
re-run coregistration I get the same result.
I guess it might have something to do with my functional scanning
parameters - I'm scanning broad coverage of cortex (just missing a bit
of motor and temporal) on a short TR (1s) and coarse resolution
(3x3x5mm). Is it generally difficult to get such low resolution, low
contrast images to coregister correctly?
(BTW on this third participant, I'm using dummy scans. On the previous
two that coregistered well, I did record the initial high-contrast
scans. Since I am using the mean of ~400 functional images as reference,
I guess those few initial scans shouldn't make a difference, but I
thought I should mention it just in case).
Of course I can simply coregister this participant by hand, but it would
be more satisfying to understand why it is going awry. Any suggestions?
thanks,
Brian
--
Brian Murphy
Post-Doctoral Researcher
Language, Interaction and Computation Lab
Centre for Mind/Brain Sciences
University of Trento
http://clic.cimec.unitn.it/brian/
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