Hi,
> I don't think it is the speed of the movement that increases the effect
> of artefacts, it really is the displacement. The artefact is due to the
> spin excitation history of the voxel, i.e. energy transmitted to a brain
> region before thatt region was at its current voxel location (maybe you
> should ask an MR physicist instead of reading this...).
Just a question - my impression was that the current thinking is that
spin-history is a rather minor factor in the motion-related variance.
Is that true? Certainly there can be quite large effects from motion
by distortion interactions - this is stuff Chloe Hutton and Jesper
Andersson have worked on.
I did a very tiny study of including movement parameters up to the 24
regressor spin-history model (which will include the effects modeled
by the difference of the parameters) and found, like Tom Johnstone,
that only the movement parameters themselves seemed to be robustly
useful:
http://www.mrc-cbu.cam.ac.uk/~matthew/abstracts/Moves/moves.html
The link points to my HBM2005 abstract.
Best,
Matthew
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