Hi Robert,
On 17 Apr 2006, at 03:57, Robert Terwilliger wrote:
> Dear FSL People,
>
> I have two questions regarding flirt's use in the
> eddy_correct shell script.
>
> 1) What is the purpose for using the -nosearch
> option?
This means that it doesn't start by trying a full range of starting
orientations of an image relative to the reference image, but only
does a local minimisation about the start position - this is done
because you can assume that the person hasn't moved their head
through 90 degrees during the session.....
>
> 2) For DTI, how do you decide to use the default
> cost function (corratio) as opposed to some other
> (e.g. normcorr)?
You need an inter-modal cost function as the different diffusion
gradient directions produce very different images from each other
(certainly not such that say one image is a scaled version of another
in general) - so an intra-modal cost function (eg normcorr) would
probably not work well. The choice of corrratio as opposed to another
intermodal cost function (eg mutualinfo) is made through experience
rather than for theoretical reasons (I think), but nutualinfo would
probably be ok too.
Cheers.
>
> Thank you,
>
> Robert Terwilliger
> University of Pittsburgh
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Stephen M. Smith, Professor of Biomedical Engineering
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