Hi Matt
Your abstrac is very intresting, could you email me a PDF of your HBM
poster? With your MP2 beeing significant in 55% of the subjects
wouldn't it be fair to always include both MP and MP2 but only
optionally MP+1 and MP2+1? I don't like the idea of including MP only
for at least one reason: "Imagine you have a GM voxel between two WM
voxels then movement in opposite direction would lead to a signal
change in the same direction which you cannot model with MP only,
right?"
Best
Torben
On 5 Oct 2005, at 17:45, Matthew Brett wrote:
> 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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