I ran 3dTshift on a dataset and am trying to
interpret the results. The offsets and
commandline are appended below. I am looking
at timecourses from slice 17, before and
after 3dTshift, as an example. Slice 17 was
acquired quite a bit later than slice 16,
since the acq order was 0,2,4...1,3,5....
So, to align slice 17 with slice 16 I expect
it needs to be interpolated to create points
earlier in time. When I compare the original
to corrected timecourse, the corrected points
appear to have been computed by interpolating
with points later in time. This gives the
effect of having the corrected timecourse
appear to have shifted backwards in time.
But for negative offsets, (-0.5 for slice
17), don't I want corrected points to be
interpolated from points previous in time,
so the effect is that the corrected curve
appears to shift forwards in time ? What is
the meaning of the sign of the fractional shift ? Are the results of 3dTshift
interpretable by this kind of visual
inspection (the apparent interpolation and
curve shifts are tiny effects) ?

3dTshift -verbose -ignore 0 -slice 16 -quintic -prefix run1_shift run1+orig
++ opening input dataset header
++ using dataset TR = 3000 ms
++ using tpattern = 0 1500 115.385 1615.39 230.769 1730.77 346.154 1846.15 461.5
39 1961.54 576.923 2076.92 692.308 2192.31 807.692 2307.69 923.077 2423.08 1038.
46 2538.46 1153.85 2653.85 1269.23 2769.23 1384.62 2884.61 ms
++ common time point set to 923.077
++ copying input dataset bricks
++ slice 0: fractional shift = 0.307692
++ slice 1: fractional shift = -0.192308
++ slice 2: fractional shift = 0.269231
++ slice 3: fractional shift = -0.230769
++ slice 4: fractional shift = 0.230769
++ slice 5: fractional shift = -0.269231
++ slice 6: fractional shift = 0.192308
++ slice 7: fractional shift = -0.307692
++ slice 8: fractional shift = 0.153846
++ slice 9: fractional shift = -0.346154
++ slice 10: fractional shift = 0.115385
++ slice 11: fractional shift = -0.384615
++ slice 12: fractional shift = 0.0769231
++ slice 13: fractional shift = -0.423077
++ slice 14: fractional shift = 0.0384615
++ slice 15: fractional shift = -0.461538
++ slice 16: fractional shift = 0
++ slice 17: fractional shift = -0.5
++ slice 18: fractional shift = -0.0384617
++ slice 19: fractional shift = -0.538461
++ slice 20: fractional shift = -0.076923
++ slice 21: fractional shift = -0.576923
++ slice 22: fractional shift = -0.115385
++ slice 23: fractional shift = -0.615384
++ slice 24: fractional shift = -0.153846
++ slice 25: fractional shift = -0.653846
++ writing output

thanks,
kate