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Hi - It is correct that the further you move away from the original grid positions the more interpolation smoothing you get. In 1D this is simple - the smoothing is 'greatest' halfway in between the gridpoints. In general we don't recommend doing such cross-run motion correction anyway - we recommend within-run motion correction and then alignment across-run later - i.e. how FEAT normally does things. Cheers. On 13 Apr 2011, at 05:42, Andreas Bartsch wrote: > Hi, > > how does the frame you correct look like? I.e. could the reason be within-slice motion to start with? > Cheers, > Andreas > > ________________________________ > Von: FSL - FMRIB's Software Library [[log in to unmask]] im Auftrag von Satrajit Ghosh [[log in to unmask]] > Gesendet: Mittwoch, 13. April 2011 06:05 > An: [log in to unmask] > Betreff: [FSL] mcflirt - interpolation question > > hi all, > > on a dataset with a fair amount of movement, we are using mcflirt to realign all images from 4 runs to the first image of the first run. we are noticing that larger differences in motion parameters are resulting in smoother "looking" images (when viewed with fslview). i couldn't figure out why that might be the case. from an interpolation perspective i don't think the amount of translation or rotation should change the smoothness of the image (especially in this rigid body case). > > any clues or solutions would be much appreciated. we are using the default parameters for mcflirt (v 4.16), and using -reffile to point to the first image of the first run. > > cheers, > > satra > --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------