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Hi, You are right that using SENSE acceleration does reduce warping. What you need to do to use FUGUE in this case (including via the FEAT gui) is to replace the dwell time with an "effective dwell time" which is the dwell time divided by the acceleration factor. This gives the equivalent time that it takes the acquisition to move between the k-space lines that would have been acquired for a single, unaccelerated, full-fov scan. This will then reduce the size of the distortions and unwarping appropriately. All the best, Mark On 5 Dec 2006, at 08:54, Johan wrote: > Dear FSL list, > > I am trying to understand how the SENSE factor (on philips scanners) > impacts the way you should unwarp your images. I understand the story > behind unwarping when you actually measure the whole k-plane, but am > confused when you do SENSE encoding. > > Should I change soms steps in the unwarping procedure, and if so, > which ones? > > > My guess is that using SENSE will create less distortions in the EPI. > A fewer number of k-lines is read, and therefore one slice takes less > time to measure... and so inhomogeneities in the field will have less > time to create distortions in the phase encode direction. The dwell > time is not altered however... just the number of k-lines you actually > read. The echo spacing is also not altered. But I don't see where or > how this would change the prelude-fugue procedure. > > Regards, > Johan