Dear spm'ers,
1) my functionnal image voxels are 3,75 x 3,75x 6 mm size. In which
cases and with what kernel should
I realign (= apply the realignment matrix to) my images? So far,
recommendations I got from different users and
methodologists varied between:
- do not realign at all if mouvement along timeseries was small, i. e.
did not exceed 2mm translation and/or 1 degree
rotation, because realignment may bring undesirable secondary effects.
If mouvement was larger, use 5mm kernel.
- realign if mouvement was large; if it was small (see above), realign
only between the first images of each series
- spm realignment proceeders are particularily effective if movement was
small (!!!). So apply them systematically
precisely in that case. For larger mouvement, use different realignment
pre-treatment (which one then?).
Can anyone help me to find my way within all these contradictions?
2) time slicing is to be applied to functionnal images before spatial
realignment. Naturally , as the
signal in each voxel has been modified by the time slicing interpolation
proceedures, we expect the realignment matrix to be different too.
However, I applied "realign correster" to my data before and after time
slicing, and the two realignment curves looked the same.
What is the exact impact of time slicing on realignement matrix?
Thanks in advance
K
--
Katia Dauchot
INSERM U483
9, quai St. Bernard, Bat C, 6me étage, 75005 PARIS
tel: 01 44 27 33 87 fax: 01 44 27 34 38
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