There are plenty of papers showing the existence of distortions in EPI
data, and I know that the rigid-body registration that you get with
Coreg does not correct these. Therefore, what is really needed is a
way of either correcting the distortions in order to make the best use
of anatomical data for spatial normalisation, or spatial normalisation
direct from the functional scans. I suspect that the former approach
will eventually lead to the best results for most fMRI data. The
field map approach should be useful here, but there are also other
strategies for doing the correction.
Best regards,
-John
On 2 August 2011 14:19, Gael Varoquaux <[log in to unmask]> wrote:
> On Tue, Aug 02, 2011 at 02:12:35PM +0100, John Ashburner wrote:
>> For many fMRI studies, the limitation in using your second method is
>> the coregistration between the fMRI and anatomical data. Distortions
>> preclude accurate rigid-body alignment, which means that normalising
>> transforms determined from the anatomical data may not work so well
>> for the functional data.
>
> Hey John,
>
> I have observed too that using the T1 doesn't always improve results,
> because of coregistration errors, and I think that have heard you
> mentionned that sometimes you normalize the EPI directly. Do you have any
> reference either showing that coregistration is a limiting factor in some
> situations, or detailling the 'other' route: normalization (hopefully
> using Dartel) of the EPI?
>
> Cheers,
>
> Gael
>
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