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Hi, first you may want to check out this: https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=spm;9a40438.03 In your case, you can still shift all your slices to the middle of your TR of 5 secs. You would do this by using slicetimer's --tcustom and acknowledging that your final slice was acquired at 2 secs (or 1.973 for the matter) which is - in fractions of TR = 5secs - indeed 2/5. Cheers, Andreas Am 17.05.12 20:55 schrieb "Sean F Walsh" unter <[log in to unmask]>: >Dear Professor Smith and Dr. Bartsch, > >Thanks a lot for the quick response. Would one of you mind dealing with >one remaining doubt of mine? > >If I understand correctly without slice-timing correction FEAT will >presume that all slices were taken after 2.5 seconds of each volume, when >in fact each of the 37 slices were taken in the first 2 seconds. As >slice-timing correction shifts "each time-series by an appropriate >fraction of a TR relative to the middle of the TR period" I presume it >will shift every time series by fractions of 5 seconds, which is not >appropriate here. Is it necessary to input a slice timings file detailing >the appropriate shift for each slice? I believe a value of 0.5 is no >shift (and would thus represent 2.5 seconds in here). > >The slices were taken in interleaving sequence (0,2.....36, 1,3,.....35). > >Must I thus calculate each slice's timing by the following formulae? > >slice X timing for even slices = (((X/2)+1)/37)*(2/5) >Where ((X/2)+1) will give each even slice its correct place in the order >of acquisition from 1-37 (not sure if this should be 0-36 or 0.5 - 36.5 >instead). I then divide by 37 in order to give each slice its time in >terms of 1 TR, with 0.5 being no shift and representing 2.5 seconds in >this case. I then multiply by (2/5) to correct for the fact that all >slices were taken in the first 2 seconds of the 5 second TR > >Similarly the formula for odd slices would be >((((x+1)/2)+19)/37)*(2/5) >where (((x+1)/2)+19) assigns each odd slice its correct place in the >order of acquisition, and once again dividing by 37 normalises this >placing to give timings in terms of 1 TR, and multiplying by (2/5) takes >into account the fact that all slices were taken in 2, not 5 seconds. > >Otherwise tips on how to modify the model times would be equally >appreciated. > >Many thanks in advance, > >Sean