Hi Jeni,
For signal loss the best way is just to look at the intensity difference.
So I would apply the distortion correction and then subtract the images and look at the intensity changes in various areas on a voxel basis, or get histograms from ROIs of interest.
For the distortion, you can take the shiftmap and calculate appropriate statistics from this - you can measure things like the standard deviation across the shiftmap, which then gives a reasonable measure of how much movement is occurring, or maybe look at certain quantiles, or the histograms.
Hope this helps.
All the best,
Mark
On 7 Sep 2012, at 03:18, Jeni Chen <[log in to unmask]> wrote:
> Hello!
>
> I've been trying the fieldmap correction with FUGUE in FEAT, and I'm just wondering whether there is a way of quantifying the amount of distortion or signal loss in the epi images, in addtion to the graphic representation in the report file. Basically we have 2 sets of epi images acquired using different parameters in attempt to reduce the signal loss in the known susceptible areas. So the idea is simply to compare the 2, before and after applying FUGUE, and knowing the amount of distortion and signal loss in each set before the correction would actually quite practical as well.
>
> Thank you in advance,
>
> Jeni
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