Hi Mike,
you can't change this retrospectively. It means that different protocols
were used when scanning (or different processing after scanning, before
passing it to freesurfer-in that case it could be fixed). It would be
good to try to understand what exactly changed between acquisitions (is
this on the same scanner/headcoil)? If it is the same scanner and no
parameters that affect the image intensity changed, I would not worry
too much about this small difference in voxel size.
You may also want to check if this happens in all subjects, or only
some. And if in some, are they all in one of your groups or distributed
across groups, to avoid potential bias.
Best, Martin
On 04/04/2016 12:07 PM, Angstadt, Mike wrote:
We have a large number of scans that have been processed through the
standard cross-sectional stream. Subjects have a number of repeated
scans, so we now want to take advantage of the longitudinal stream.
When first beginning to run subjects through longitudinal template
creation, we noticed a warning message in some cases in the log:
*******************************************************************************
WARNING: Image geometries differ across time, maybe due to aquisition
changes?
This can potentially bias a longitudinal study! Will continue
in 10s.
*******************************************************************************
Looking into it, there does indeed appear to have been a change in the
reconstruction stream that led to images at different times during the
study to have slightly different voxel dimensions, changing from
1x1x1.2 to 1.01x1.01x1.2mm voxels.
Our question is if there is some way to fix this prior to starting the
longitudinal stream but without having to redo the original
cross-sectional processing and editing that has been completed?
--
Mike Angstadt
Research Computer Specialist / PANLab Lab Manager
Department of Psychiatry / University of Michigan
(734) 936-8229
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--
Martin Reuter, PhD
Assistant Professor of Radiology, Harvard Medical School
Assistant Professor of Neurology, Harvard Medical School
A.A.Martinos Center for Biomedical Imaging
Massachusetts General Hospital
Research Affiliate, CSAIL, MIT
Phone: +1-617-724-5652
Web : http://reuter.mit.edu
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