Dear Katrin and Julia
This procedure is used to account for residual movement artifacts. The
procedure is described in a paper by Karl in 1996:
@article{Friston96,
Author = {Friston, K. J. and Williams, S. and Howard, R. and Franckowiak,
R. S. J. and Turner, R.},
Journal = {Magn Reson Med},
Pages = {346-355},
Title = {{Movement-Related effects in {f{MRI}} time series}},
Volume = {35},
Year = {1996}}
My general impression is that the effects are always present.
Hope this helps
Torben
Torben E. Lund
Danish Research Centre for MR
Copenhagen University Hospital
Kettegaard Allé 30
2650 Hvidovre
Denmark
email: [log in to unmask]
webpage: http://www.drcmr.dk
> Dear SPM,
>
> once again a question concerning the use of the realignment parameters as
> regressors in the design matrix:
>
> Some people first use these parameters to reduce differences between
> certain volumes and the reference volume during preprocessing and then
> include them again in the design matrix. But don´t you apply these
> regressors on data that are changed according to these regressors in this
> case?
>
> In other words: In the first step you estimate parameters that explain a
> certain amount of variability in the data. Then you change the data
> according to these parameters (reslicing the data). If you now include the
> movement parameters in the design matrix they explain variance in data
> that does not exist like that anymore.
>
> confused greetings,
> Katrin and Julia
>
>
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